Humans & natural selection

  • 41 Replies
  • 12591 Views

0 Members and 1 Guest are viewing this topic.

*

Offline harrypalmer

  • Jr. Member
  • **
  • 11
    • View Profile
Humans & natural selection
« on: 18/10/2005 10:55:45 »
I was wondering to what extent humans are now subject to natural selection.

In the past humans as with other species would have had to adapt to survive, and of course those best suited to certain niches would have survived, but isnt it different now?

Man has the ability to alter his living conditions (to a degree). In addition we are for the most part a compassionate species and care for our sick and disadvantaged. Surely by doing so we are 'interfering' with the normal process of evolution, whereby the fittest or best adapted survive?

Dont get me wrong Im all for compassion, and we still havent got it right across the globe. I am just looking at it from a purely scientific view.

Are we now the exception to the norm on this planet, and the only species no longer evolving purely to survive?

Any thoughts?
 

*

Offline Ultima

  • Sr. Member
  • ****
  • 488
    • View Profile
    • My Homepage
Re: Humans & natural selection
« Reply #1 on: 18/10/2005 19:57:59 »
Yeah I asked this a while ago. Plus does the media and social trend have an impact :D
So long as the human "ideal" form doesn't change to rapidly in society we might slowly evolve towards it. Mentally I think there is going to be a lot of evolution in the future... saying that though you don't need to be intelligent to procreate, it's probably to the contrary [:D].

RISE OF THE CHAVS and stick thin top-heavy people!
wOw the world spins?

*

Offline thefunkyaquarium

  • First timers
  • *
  • 4
    • View Profile
    • http://www-jcsu.jesus.cam.ac.uk/~lw310
Re: Humans & natural selection
« Reply #2 on: 18/10/2005 20:39:30 »
The thing is, nowadays pretty much everybody can reproduce - even those with genetic defects (as long as they're mild enough for survival).  Poor eyesight, low intelligence, ugliness... they don't stop people from finding partners and having children.

Note also that people who are better off (professional classes, etc) are having fewer children...

So I say natural selection is working the opposite way in humans, and several hundred generations down the line we'll all be weaklings [:)]
 

*

Offline harrypalmer

  • Jr. Member
  • **
  • 11
    • View Profile
Re: Humans & natural selection
« Reply #3 on: 18/10/2005 20:55:23 »
Someone I know has raised the possibility that humans may now evolve with an iPod socket.

:S
 

*

Offline harrypalmer

  • Jr. Member
  • **
  • 11
    • View Profile
Re: Humans & natural selection
« Reply #4 on: 18/10/2005 20:59:18 »
The other thing to consider is whether people in poorly developed countries are evolving differently to us in the affluent West?

We think of ourselves as healthier and stronger, but I suspect we are not.

I remember seeing in Zimbabwe a young local lad pick up a piece of rail track in his teeth that a full grown man from the UK couldnt even lift in his arms.

It was an amazing sight. :)
 

*

Offline Ultima

  • Sr. Member
  • ****
  • 488
    • View Profile
    • My Homepage
Re: Humans & natural selection
« Reply #5 on: 18/10/2005 22:41:10 »
Yeah everyone in Africa is going to become immune to HIV which means we will be screwed. Except we have the money and technology to steal their genes [:D].
wOw the world spins?

*

Offline Simmer

  • Sr. Member
  • ****
  • 229
    • View Profile
Re: Humans & natural selection
« Reply #6 on: 19/10/2005 20:53:23 »
We have to be careful not to confuse selective breeding with natural selection.  Ordinary people breeding faster than lawyers or scientists has nothing to do with natural selection; all are human, even the lawyers.

Natural selection applies to mutations, a change in genetic makeup that confers some new trait or ability.  Those mutations are still going on throughout our species even if the selection part isn't operating fully at the moment.  So we are storing up all those new traits, ready to put to the test once times get hard again [:D]
 

*

another_someone

  • Guest
Re: Humans & natural selection
« Reply #7 on: 20/10/2005 00:17:38 »
quote:
Originally posted by Simmer

We have to be careful not to confuse selective breeding with natural selection.  Ordinary people breeding faster than lawyers or scientists has nothing to do with natural selection; all are human, even the lawyers.

Natural selection applies to mutations, a change in genetic makeup that confers some new trait or ability.  Those mutations are still going on throughout our species even if the selection part isn't operating fully at the moment.  So we are storing up all those new traits, ready to put to the test once times get hard again [:D]



I'm sorry, but I don't see the difference.

Why should selection restrict itself to mutations?

What is generally true is that we have very few truly isolated populations, so we cannot develop the inbreeding required for speciation (i.e. most of the little changes get swamped by the vast number of unchanged genes).  One area where we do have a slightly isolated population is the increased number of people born with inheritable deafness since the development of sign language (which allows deaf people to communicate between themselves, but relatively few hearing people are able to communicate with sign language, thus creating a distinct and separate deaf culture).

I would say the selection part is ongoing within our society, but the selection is geared more towards fitness for our social environment than fitness for the physical environment.  One area where this might be happening is with the pressure towards ever delayed child bearing, that women who have a predisposition to early menopause should be being bred out of our society (it would also have the effect of increasing life expectancy, which is clearly being observed).

quote:
Originally posted by thefunkyaquarium

The thing is, nowadays pretty much everybody can reproduce - even those with genetic defects (as long as they're mild enough for survival).  Poor eyesight, low intelligence, ugliness... they don't stop people from finding partners and having children.

Note also that people who are better off (professional classes, etc) are having fewer children...

So I say natural selection is working the opposite way in humans, and several hundred generations down the line we'll all be weaklings [:)]



What is a genetic defect?

Does not the term 'defect' imply a presumption of some notion of normality - but is not the notion of evolution based on the premise that there is no such thing as normal, only that which survives, and that which fails to survive.  In fact, normality is a notion of conservation, which is the antithesis of evolution.

There are many successful species of animals that are blind, so the fact that some humans are born with inferior eyesight does not make them 'defective', only different.

The fact that professional classes are having fewer children, firstly has to be balanced against the fact that the children of the professional classes generally have a better survival rate, but it also must be remembered that a society that only bred rocket scientists would be a very unbalanced society.

On the broader front, humans are an intensely social animal (more social than any other mammal, and comparable only to some insects), and so you should not be looking at the strengths and weaknesses of the individual, but rather the strengths and weaknesses of the society.  The weaknesses of an individual are irrelevant if they perform a useful function to enhance the survival of their society.  As I indicated above, a society needs only just so many rocket scientists, but it needs a lot more plumbers, labourers, and refuse collectors.

*

Offline Simmer

  • Sr. Member
  • ****
  • 229
    • View Profile
Re: Humans & natural selection
« Reply #8 on: 22/10/2005 22:27:14 »
quote:
Originally posted by another_someone
[brI'm sorry, but I don't see the difference.

Why should selection restrict itself to mutations?

What is generally true is that we have very few truly isolated populations, so we cannot develop the inbreeding required for speciation (i.e. most of the little changes get swamped by the vast number of unchanged genes).  One area where we do have a slightly isolated population is the increased number of people born with inheritable deafness since the development of sign language (which allows deaf people to communicate between themselves, but relatively few hearing people are able to communicate with sign language, thus creating a distinct and separate deaf culture).

I would say the selection part is ongoing within our society, but the selection is geared more towards fitness for our social environment than fitness for the physical environment.  One area where this might be happening is with the pressure towards ever delayed child bearing, that women who have a predisposition to early menopause should be being bred out of our society (it would also have the effect of increasing life expectancy, which is clearly being observed).



I take your point about selection still occuring in some respects, in particular your example of selection against early menopause was very interesting.  I'm not convinced about the life expectancy example though, I think that has more to do with diet, sanitation and medicine.

However, I believe that natural selection applies only to mutations because otherwise selection is ultimately inconsequential.  You could selectively breed for minor traits like height, eye colour or some such but, because you are breeding human with human, at the end of the day you will end up with a creature with exactly the same genetic potential as when you started (assuming you didn't inbreed too much).  If you then left that population alone for enough generations it would become indistinguishable from the unselected population in a similar environment. Permanent significant change can only occur through a successful mutation.
 

*

Offline Titanscape

  • Hero Member
  • *****
  • 785
    • View Profile
Re: Humans & natural selection
« Reply #9 on: 23/10/2005 13:35:39 »
I heard that the present generation has a higher IQ than the last. People can really only have children if they can afford to. People meet at college and University. One needs drive and intelligence to have children.

Pentecostals have a big growth rate, having many children per couple, making one of the reasons the church has grown from a hundred to 500,000,000 in 100 years. Not strictly all are called Pentecostals.

Titanscape
Titanscape

*

another_someone

  • Guest
Re: Humans & natural selection
« Reply #10 on: 24/10/2005 02:17:58 »
quote:
Originally posted by Simmer

I take your point about selection still occurring in some respects, in particular your example of selection against early menopause was very interesting.  I'm not convinced about the life expectancy example though, I think that has more to do with diet, sanitation and medicine.



The issue about life expectancy has been shown to be true in fruit flies, where fruit flies were bred with the early offspring of the females being killed off, and only the later offspring being allowed to survive.  There was a substantial increase in the lifespan of the fruit flies.

What may be argued is that humans are rather unusual in that we already live so far beyond our reproductive years that the same effect may not necessarily apply to us.

quote:
Originally posted by Simmer
However, I believe that natural selection applies only to mutations because otherwise selection is ultimately inconsequential.  You could selectively breed for minor traits like height, eye colour or some such but, because you are breeding human with human, at the end of the day you will end up with a creature with exactly the same genetic potential as when you started (assuming you didn't inbreed too much).  If you then left that population alone for enough generations it would become indistinguishable from the unselected population in a similar environment. Permanent significant change can only occur through a successful mutation.



There are two different issues here, whether the genetic changes in population are significant, and whether they are reversible.

I did say that without having a small isolated population that is inbreeding you will not get speciation, and without speciation, you will always be able to reverse any genetic change.  Even genetic mutations (such as Huntington's chorea) will not be be able to create a new species unless one has a small isolated population.

On the other hand, many of the genetic differences that exist between populations are more than merely superficial.  Differences in skin colour between races are an adaptation to different amounts of sunlight they are exposed to.  The small and rotund figures of people living in the artic regions again is a reflection of a need to minimise heat loss.  Similarly, diseases such as thalassemia and sickle cell anaemia are adaptations to the level of malaria the populations are exposed to.

http://en.wikipedia.org/wiki/Thallasemia
{quote]
Being a carrier of the disease confers a degree of protection against malaria, and is quite common among people from Italian or Greek origin, since malaria was widespread in those countries at one time. In that respect it resembles another genetic disorder, sickle-cell disease. The disease's geographical association with the Mediterranean sea was responsible for its naming: Thalassa is Greek for the sea. However it is also widespread in the Indian subcontinent.
[/quote]


*

Offline daveshorts

  • Moderator
  • Neilep Level Member
  • *****
  • 2583
  • Physics, Experiments
    • View Profile
    • http://www.chaosscience.org.uk
Re: Humans & natural selection
« Reply #11 on: 24/10/2005 17:16:49 »
I think the really strong selection effect at work at the moment is to be too incompetent to use contreception - this may have worrying long term consequences...

*

another_someone

  • Guest
Re: Humans & natural selection
« Reply #12 on: 24/10/2005 21:20:55 »
quote:
Originally posted by daveshorts

I think the really strong selection effect at work at the moment is to be too incompetent to use contreception - this may have worrying long term consequences...



It may have long term consequences, just as being easily brainwashed into overusing contraception (the other side of the same coin) may have long term consequences.  Who is to say which of those consequences will ultimately prove positive and which negative (or even how we should judge what is positive or negative)?

*

Offline Simmer

  • Sr. Member
  • ****
  • 229
    • View Profile
Re: Humans & natural selection
« Reply #13 on: 27/10/2005 00:39:41 »
quote:
Originally posted by another_someone

[I did say that without having a small isolated population that is inbreeding you will not get speciation, and without speciation, you will always be able to reverse any genetic change.  Even genetic mutations (such as Huntington's chorea) will not be be able to create a new species unless one has a small isolated population.


I think you can get permanent genetic change in a mainstream population, although it takes a while.  A successful mutation that in some way improves the probability of successful reproduction above that of the mainstream will eventually spread to the entire population.

quote:
On the other hand, many of the genetic differences that exist between populations are more than merely superficial.  Differences in skin colour between races are an adaptation to different amounts of sunlight they are exposed to.  The small and rotund figures of people living in the artic regions again is a reflection of a need to minimise heat loss.  Similarly, diseases such as thalassemia and sickle cell anaemia are adaptations to the level of malaria the populations are exposed to.


Depends how you define superficial!  I reckon if you stuck a population of Eskimo's down in Kenya and a population of Kenyans down in Alaska, 10,000 years later you would wonder why you bothered![:)]

I think it likely that within every human population there is the genetic potential to adapt to an environment in the same way as any other human population. I would call the mechanism for that selective breeding and reversible if the environment changes again; skin colour and body shape are examples of such adaptions.  I was wrong to call them superficial but they are qualitatively different from the changes that result in the development of a new species.

And I can prove it using the variously shaped and coloured human species, QED! [:D]
 

*

another_someone

  • Guest
Re: Humans & natural selection
« Reply #14 on: 28/10/2005 03:46:47 »
quote:
Originally posted by Simmer

I think it likely that within every human population there is the genetic potential to adapt to an environment in the same way as any other human population. I would call the mechanism for that selective breeding and reversible if the environment changes again; skin colour and body shape are examples of such adaptions.  I was wrong to call them superficial but they are qualitatively different from the changes that result in the development of a new species.

And I can prove it using the variously shaped and coloured human species, QED! [:D]



There are differences between racial (breed) changes and species changes, but that distinction is different to the issue of reversibility or mutation.

Two different species are defined as two populations that are incapable of interbreeding.  By definition, this means that the members of the new species do not breed with members of the old species.

What you are suggesting is a scenario where, over a long period of time, a large population contains members of a new species and members of an old species, and yet continue to interbreed - yet the very fact of their interbreeding means they cannot be two distinct species.

Nor is there any evidence that a single mutation can create a new species.  On the contrary, we know of many mutations that regularly occur within the human species which do not create speciation (Huntington's is one, and the victims of thalidomide are another).  Even if a single mutation did create someone of a new species, it would have to create a male and a female of that new species, since, if they were truly a new species, they would not be able to interbreed with members of the old species.

Nor is it clear that random mutation is a basis for speciation.  There are many cases where nature has converged upon a similar solution from different directions.  It is clear that if nature relied upon merely random mutations, each solution should be different.  The fact that it is not implies to me that most species must already have the genetic basis for filling a large number of different niches, and much of the speciation must occur by the rearrangement of existing genes rather than the creation of new genes.  This is not to say that random gene mutations do not occur (clearly, they do), only to question whether they are a prerequisite for speciation, or even a mechanism that would itself produce speciation.

*

Offline Ultima

  • Sr. Member
  • ****
  • 488
    • View Profile
    • My Homepage
Re: Humans & natural selection
« Reply #15 on: 29/10/2005 17:00:01 »
quote:
I heard that the present generation has a higher IQ than the last. People can really only have children if they can afford to. People meet at college and University. One needs drive and intelligence to have children.


Nice idea but there is another prerequisite for children, and that's sex. I'm afraid it's the retarded masses that are having children at a young age and continuing to do so throughout their lives. I guess this might not be so noticeable in Australia, but the UK has one of the highest teen pregnancy rates among industrialised countries. Only overtaken by the USA. I know this is a fairly loaded comment but I am not referring to the women who choose to have children at a young age. I am referring to the stupid teens that have no idea what they are doing, or what the long term outcome will be. I have no problem with them having sex; but tbh what chances do their children have if the parents are unable to provide.
wOw the world spins?

*

Offline Simmer

  • Sr. Member
  • ****
  • 229
    • View Profile
Re: Humans & natural selection
« Reply #16 on: 29/10/2005 18:56:21 »
quote:
Originally posted by another_someone

Two different species are defined as two populations that are incapable of interbreeding.  By definition, this means that the members of the new species do not breed with members of the old species.

What you are suggesting is a scenario where, over a long period of time, a large population contains members of a new species and members of an old species, and yet continue to interbreed - yet the very fact of their interbreeding means they cannot be two distinct species.


I think it's a cumalative thing, a mutation that prevents interbreeding with the unmutated general population will fail but if it doesn't and confers an advantage then it spreads to the whole population.  It may be that if a section of the main population is isolated for a long period then the accumulated divergence between the two sections make them incapable of interbreeding but usually the significant differences are between the current generation and their distant ancestors.

The main reason I am championing this model so vigorously is that the selection argument so often gets twisted into the elitist "only the best people should be allowed to breed". It's complete rubbish, graduates don't have children measurably brighter than anyone else, for example, and past attempts to selectively breed a noble elite have produced nothing better than haemophilia and receeding chins. [:)]

As far as the perpetuation of the human genome is concerned it really doesn't matter who the parents are unless they have some new and useful bit of code to pass on - and that virtue is randomly distributed throughout the entire population.

 

*

another_someone

  • Guest
Re: Humans & natural selection
« Reply #17 on: 29/10/2005 19:15:38 »
quote:
Originally posted by Ultima

Nice idea but there is another prerequisite for children, and that's sex. I'm afraid it's the retarded masses that are having children at a young age and continuing to do so throughout their lives. I guess this might not be so noticeable in Australia, but the UK has one of the highest teen pregnancy rates among industrialised countries. Only overtaken by the USA. I know this is a fairly loaded comment but I am not referring to the women who choose to have children at a young age. I am referring to the stupid teens that have no idea what they are doing, or what the long term outcome will be. I have no problem with them having sex; but tbh what chances do their children have if the parents are unable to provide.



It is perjoritive and inaccurate to talk about 'retarded masses'.  That they are the 'masses' would imply an element of normality about them.

As to whether 'stupid teens' actually 'have no idea what they are doing' is also uncertain.  This is something that is often said of them, but it is not something I have heard them say for themselves.

I suspect that in many cases these teens, who don't see themselves making much of their lives, feel that at least in making a baby they are making something.  I suspect it is not always as thoughtless as outsiders accuse them of (although it may be a highly emotionally charged rational - as anything to do with sex often is).

In a country where the population is having difficulty maintaining itself, and with fears that there will in future years not be enough tax payers to pay for the aging population; may it not be said that these girls are performing a public service - at least some kids are getting born.

Furthermore, as I pointed out before, this country has a greater shortage of plumbers than it has a shortage of rocket scientists.

*

Offline Ultima

  • Sr. Member
  • ****
  • 488
    • View Profile
    • My Homepage
Re: Humans & natural selection
« Reply #18 on: 29/10/2005 20:16:27 »
quote:
I suspect that in many cases these teens, who don't see themselves making much of their lives, feel that at least in making a baby they are making something.


That is fairly thoughtless, get a pet! Or even better make something of your life. The tax payer’s money goes on benefits for all of these (more often than not) single parents! WTF is this plumbing thing??? I think it's better for people to enter a trade they would be good at, than have the miss guided view that a degree == job with money. Plus plumbers make an absolute mint compared to scientists. The retardation I am alluding to is not intellectual, it is emotional, spiritual and social!

I very much doubt any of these people have seriously thought about what it might mean to have a child, and how their actions will effect there own lives and that of their child. All the ones I see on my estate back home think it's some sort of game everyone plays!


I am not saying that choosing to be a mother rather than anything else is a problem, it's the fact that these babies are being born to CHILDREN! Most of them you wouldn't trust to look after a dog! Would any adoption agency in their right mind give a baby to a teenager?


I don't know how this would effect any evolutionary process but it will have a dramatic impact on society, if we continue this trend.
« Last Edit: 29/10/2005 20:21:40 by Ultima »
wOw the world spins?

*

another_someone

  • Guest
Re: Humans & natural selection
« Reply #19 on: 29/10/2005 20:20:51 »
quote:
Originally posted by Simmer

I think it's a cumalative thing, a mutation that prevents interbreeding with the unmutated general population will fail but if it doesn't and confers an advantage then it spreads to the whole population.  It may be that if a section of the main population is isolated for a long period then the accumulated divergence between the two sections make them incapable of interbreeding but usually the significant differences are between the current generation and their distant ancestors.



There is much difference of opinion as to whether evolution develops at a constant and gradual pace, or with long periods of stasis, followed by brief period of rapid change.

If evolution does progress at a steady rate, then we should expect partial speciation.  Certainly, in human terms, the evidence is that populations that probably have not shared a common ancestor for at least 10,000 years, and maybe 30,000 years, have absolutely no disadvantage when interbreeding.

It is interesting to look at the comparison of Neanderthal man and modern man.  Neanderthals lived from 230,000 years ago to about 30,000 years ago (there is still no conclusive proof, and still some debate, as to whether Neanderthals were a different species, or just a different race; but the dominant view is presently that they were a distinct species).  If your notion of gradual change were true, one should expect a gradual change towards modern man over the period of 200,000 years.  In fact, modern man arrived over a fairly short period of time around 120,000 years ago (no-one can say exactly when the change happened because it was a case of one moment none were visible, next moment - in archaeological time -  the new species was there).

Another issue I have with your assessment is the assumption that at any given time a particular species is less than optimal, and thus a new gene would actually produce a better human being.  I know of no evidence for this, and I don't believe it is so.  A species has to adapt because of changing environmental circumstances (it may be loss of habitat, change of weather, change of population density, change of competition with other species), but this is different from assuming that once adaptation has occurred, that the species could be made better adapted to that environment if only it had a new gene to do it with.

That having been said, it is true that the environment is constantly changing (sometimes rapidly, sometimes slowly, but it always changes), and so the stresses and  challenges upon all species is always changing.  Thus, one might say that a new gene may possibly be useful in adapting to a change, but this is different from saying it would make human beings better able to adapt to the environment of yesteryear.

quote:

The main reason I am championing this model so vigorously is that the selection argument so often gets twisted into the elitist "only the best people should be allowed to breed". It's complete rubbish, graduates don't have children measurably brighter than anyone else, for example, and past attempts to selectively breed a noble elite have produced nothing better than haemophilia and receeding chins. [:)]



I commend your motivation, but not your conclusion.

All that I know implies that you are wrong in stating that IQ is not inheritable.  Although clearly poor diet can constrain IQ, but given an adequate diet, I understand that IQ is largely determined by prenatal levels of testosterone, and is controlled by a gene (or genes) on the X chromosome, and thus inherited through the maternal line.  On the other hand, educational attainment is not always simply a matter of IQ (I know many people with high IQ who got so bored at school that they performed considerably worse than other children with lower IQs).

Where I agree with you is that selective breeding is counterproductive, but not because the traits are not inheritable, but because extreme thoroughbreds are unhealthy, and because in nature there is no such thing as 'best'.  That which may be 'best' in one niche, when the environment changes, even slightly, then that 'best' suddenly becomes a liability.  Human beings, if they have had any virtue, has been in their versatility and adaptability, not in their ability to specialise.  The Giant Panda is a specialist, and is consequently an endangered species because its native environment is under threat.


*

another_someone

  • Guest
Re: Humans & natural selection
« Reply #20 on: 29/10/2005 21:06:04 »
quote:
Originally posted by Ultima

That is fairly thoughtless, get a pet! Or even better make something of your life. The tax payer’s money goes on benefits for all of these (more often than not) single parents! WTF is this plumbing thing??? I think it's better for people to enter a trade they would be good at, than have the miss guided view that a degree == job with money. Plus plumbers make an absolute mint compared to scientists. The retardation I am alluding to is not intellectual, it is emotional, spiritual and social!

I very much doubt any of these people have seriously thought about what it might mean to have a child, and how their actions will effect there own lives and that of their child. All the ones I see on my estate back home think it's some sort of game everyone plays!

I am not saying that choosing to be a mother rather than anything else is a problem, it's the fact that these babies are being born to CHILDREN! Most of them you wouldn't trust to look after a dog! Would any adoption agency in their right mind give a baby to a teenager?

I don't know how this would effect any evolutionary process but it will have a dramatic impact on society, if we continue this trend.



Firstly, the notion of teenagers being children is fairly modern.  In the 17th century, 15 year old wives and mothers were not at all uncommon.

Yes, society has changed, and you can say that you are concerned to perpetuate 20th century social norms, and would see teenage pregnancy as a threat to that.  This is reasonable, but the 20th century cannot stay forever.

A far more serious long term threat to society is population implosion.

http://news.bbc.co.uk/1/hi/world/asia-pacific/3708098.stm
quote:

The name Sony summons visions of all things Japanese. Yet its board chairman, Iwao Nakatani, recently called for mass immigration, opening Japan to different faces and influences.
Mr Nakatani is worried because Japanese are living longer, yet having fewer children. The result is a shrinking workforce which threatens economic growth.



What is true of Japan is true of all modern societies.  So you would wish for mass immigration, but would condemn the few who would have children in this country.

I accept that no adoption agency would ever (in the present political climate) give a child to a teenage mother for adoption.  This is a political issue above all else.

I would also agree that it may well be that many of these young mothers (possible for reasons beyond their mere age) would not make the best of mothers; but since many others who may be better mothers are choosing not to be mothers at all, it may well be that we have a choice between a imperfect mothers or no mothers.  Maybe it might be better if we focus on making them better mothers, rather than simply condemn them for choosing to be mothers.

*

Offline Simmer

  • Sr. Member
  • ****
  • 229
    • View Profile
Re: Humans & natural selection
« Reply #21 on: 29/10/2005 23:04:20 »
quote:
Originally posted by another_someone


If your notion of gradual change were true, one should expect a gradual change towards modern man over the period of 200,000 years.  In fact, modern man arrived over a fairly short period of time around 120,000 years ago (no-one can say exactly when the change happened because it was a case of one moment none were visible, next moment - in archaeological time -  the new species was there).

Another issue I have with your assessment is the assumption that at any given time a particular species is less than optimal, and thus a new gene would actually produce a better human being.  I know of no evidence for this, and I don't believe it is so.  A species has to adapt because of changing environmental circumstances (it may be loss of habitat, change of weather, change of population density, change of competition with other species), but this is different from assuming that once adaptation has occurred, that the species could be made better adapted to that environment if only it had a new gene to do it with.

That having been said, it is true that the environment is constantly changing (sometimes rapidly, sometimes slowly, but it always changes), and so the stresses and  challenges upon all species is always changing.  Thus, one might say that a new gene may possibly be useful in adapting to a change, but this is different from saying it would make human beings better able to adapt to the environment of yesteryear.

All that I know implies that you are wrong in stating that IQ is not inheritable.  Although clearly poor diet can constrain IQ, but given an adequate diet, I understand that IQ is largely determined by prenatal levels of testosterone, and is controlled by a gene (or genes) on the X chromosome, and thus inherited through the maternal line.  



If we're not careful the next generation will be inheriting this thread too! [:)]  

For the sake of argument I'm willing to concede that inherited traits may include IQ (really testosterone?) and that human beings suddenly appeared, fully fledged as it were, 120,000 years ago.

Given all that what do you think the mechanism that produced that first human was?
 

*

another_someone

  • Guest
Re: Humans & natural selection
« Reply #22 on: 30/10/2005 17:23:11 »
quote:
Originally posted by Simmer

For the sake of argument I'm willing to concede that inherited traits may include IQ (really testosterone?) and that human beings suddenly appeared, fully fledged as it were, 120,000 years ago.

Given all that what do you think the mechanism that produced that first human was?



One thing I have found while trying to find an answer to this question is that I was wrong to say that modern humans evolved from Neanderthal man.  It seems the current consensus is that both are derived, at different times,  directly from H. heidelbergensis.

The more I tried to look for answers as to why it is thought these species diverged, the more confused I became, until I began to even question whether we know whether they are distinct species or not.  They look different, but then a Great Dane looks very different to a Chihuahua.  The common assumption is that these groups, who co-existed for many tens of thousands of years, did not interbreed; and yet even that is not certain.

Because so much is unknown about the exact relationship of early humans, I will avoid directly answering the question about human speciation, but will go try and generalise about speciation.

http://en.wikipedia.org/wiki/Coelacanth
quote:

The first hint that western scientists had of a modern, living coelacanth existed was when Marjorie Courtenay-Latimer, who was curator of a museum in East London, South Africa, was inspecting local fish catches for unusual specimens in 1938.


http://en.wikipedia.org/wiki/Coelacanth
quote:

Coelacanths were believed to first appear in the Carboniferous Period, about 400-350 million years ago.



If we are indeed dealing with the same species (even if they look the same, it would be very difficult to conclusively prove they could interbreed), then we are dealing with a species that survived for over 350 millions years.

http://en.wikipedia.org/wiki/Living_fossil
quote:

The mean species turnover time (the time a species lasts before it is replaced) varies widely among the phyla, but is about 2-3 million years.



If the average is 2-3 million years, and the longest is 350 million years, then the shortest time a species must exist (be created, and then disappear) must be very much shorter than 2 million years.

If speciation were merely the consequence of random mutations over time, causing species to slowly drift away from their original form, one would not expect such widely varying rates of change.

The fact that a species can survive for 350 million years (or even a mere 2 million years) would imply to me that there must be substantial processes in place that conserve the genome of the species, and that some significant external force must be applied overcome this inertia.  The fact that some species can be created, and disappear, in a very much shorter period of time, would imply that the force that can overcome the species inertia is not constant.

We know that on an individual level, there are factors that can alter the probability of mutation (e.g. age of parent, viral infection – and by inference, the effectiveness of the parental immune system, and that might be effected by environmental stresses).  This alone might have an impact that would allow the mechanisms that conserve the species to be overwhelmed by a large number of mutants at times of high environmental stress.  This might then be further exaggerated by significant inbreeding if a small population is cut off from the mainstream population.  Once the mechanisms for conserving the species have been overcome, then it would be a competition between the various mutants as to which will be sufficiently successful to create a new niche for itself in which it can thrive as a new species (possibly several new species – derived from the same parent species - being successful, causing a rapid radiation of new species as is often seen after a mass extinction event).

*

Offline Simmer

  • Sr. Member
  • ****
  • 229
    • View Profile
Re: Humans & natural selection
« Reply #23 on: 30/10/2005 22:54:24 »
quote:
Originally posted by another_someone

We know that on an individual level, there are factors that can alter the probability of mutation (e.g. age of parent, viral infection – and by inference, the effectiveness of the parental immune system, and that might be effected by environmental stresses).  This alone might have an impact that would allow the mechanisms that conserve the species to be overwhelmed by a large number of mutants at times of high environmental stress.  This might then be further exaggerated by significant inbreeding if a small population is cut off from the mainstream population.  Once the mechanisms for conserving the species have been overcome, then it would be a competition between the various mutants as to which will be sufficiently successful to create a new niche for itself in which it can thrive as a new species (possibly several new species – derived from the same parent species - being successful, causing a rapid radiation of new species as is often seen after a mass extinction event).


Nice try, another someone - actually a very nice try! [:)] If the mutation rate does increase in response to environmental stress that would be, as you say, a highly significant evolutionary mechanism.  But before you submit this thread to Nature, is it true? It doesn't seem to affect human mitochondrial DNA, for example, the mutation rate of which is believed to be so regular that it is used to date prehistoric human migration.

A steady rate of mutation can also explain phenomena like coelacanths and other long lived species - a mutation doesn't persist unless it offers some advantage, or at least no disadvantage.  In a well adapted creature in a stable environment most mutations would be less successful than the normal population and eventually be bred out.

Steady mutation rates can also explain the explosion of speciation after a mass extinction.  A regularly occuring mutation that let a well adapted nut-eating bird become a poorly adapted seed eating bird would normally be a disadvantage and be bred out every time it cropped up, unless all the well adapted seed eaters were dead and there was a niche for these mutants to survive in and become adapted to.

Of course all that is just rationalisation of my original standpoint - I don't really know which of us is right (if either!) but at the very least you have convinced me that the there are a lot of possible mechanisms that I hadn't previously considered [:)]
 

*

another_someone

  • Guest
Re: Humans & natural selection
« Reply #24 on: 31/10/2005 16:26:45 »
quote:
Originally posted by Simmer

If the mutation rate does increase in response to environmental stress that would be, as you say, a highly significant evolutionary mechanism.  But before you submit this thread to Nature, is it true? It doesn't seem to affect human mitochondrial DNA, for example, the mutation rate of which is believed to be so regular that it is used to date prehistoric human migration.



Is it true? – I cannot say, I am no expert on the matter, only trying to apply rational logic to what little I know.

I have two answers with regard to mitochondrial DNA.

Firstly, we cannot at all be sure that the rate of change does not alter in times of stress – when have we observed human mitochondria on a population wide basis under stress conditions?

Secondly, to what extent does mitochondrial DNA really give us information about speciation?

Mitochondria is inherited solely from the mother, yet the definition of a species depends on the way sexual reproduction behaves.  Mitochondria are not directly affected by sexual reproduction, since it has no input from the paternal line.

In particular, in sexual reproduction, there is much shuffling around of genes between the chromosomes of the two parents.  This shuffling around can cause all sorts of transcription errors, and problems with improper pairing of chromosomes.  In all of this, the mitochondria remain unaffected, and thus far more conserved and stable.  This is what made mitochondria such an easy target for tracing a maternal lineage, but it also makes it very different in nature to the chromosomes that are within the cell nucleus.

Another anomaly that arises is from a similar project that traced the human maternal line through mitochondria, but this traced the paternal line through the Y chomosome.

http://news.bbc.co.uk/1/hi/sci/tech/999030.stm
quote:

The most recent ancestor of all males living today was a man who lived in Africa around 59,000 years ago, according to an international team of researchers.
The scientists from eight countries have drawn up a genetic family tree of mankind by studying variations in the Y chromosome of more than a thousand men from different communities around the world. The Y chromosome is one of the two sex chromosomes (X and Y) which only men carry (women carry two X chromosomes).
The new research confirms the Out of Africa theory that modern humans originated in Africa before slowly spreading across the world.
But the finding raises new questions, not least because our most recent paternal ancestor would have been about 84,000 years younger than our maternal one.


http://news.bbc.co.uk/1/hi/sci/tech/999030.stm
quote:

This Out of Africa hypothesis has been confirmed by studies of mitochondrial DNA, the segment of genetic material that is inherited exclusively from the mother.
Based on these studies, our most recent common ancestor is thought to be a woman who lived in Africa some 143,000 years ago, the so-called Mitochondrial Eve.



Since the nature of a species is that the mate of an individual of a species must also be from the same species, this leaves three possibilities:

Either the clocks are wrong, and these two ancestors did live at the same time.

Or, mitochondrial Eve was not human.  All the trace can really tell us is that all living human females are related to mitochondrial Eve, they cannot tell us what species mitochondrial Eve actually was.

Or, Y chromosome Adam was not the first human male.  All the trace can tell us is that all living males are related to Y chromosome Adam, they but by inference, we must also be related to his father, his grandfather, his great grandfather, etc.

None of this really tells us very much about where the boundary between one species and another occurred.  In other words, if we were able to travel back in time, which of our ancestors could we successfully mate with, and and which point in time would we first come across an ancestor we are no longer able to mate with?

quote:

A steady rate of mutation can also explain phenomena like coelacanths and other long lived species - a mutation doesn't persist unless it offers some advantage, or at least no disadvantage.  In a well adapted creature in a stable environment most mutations would be less successful than the normal population and eventually be bred out.



This is half the answer.

The fact is that most mutations do not cause speciation.

Humans have invaded a very wide variety of environments, and one way or another, have adapted to those environments.  Some of those adaptations have been through mutation and selection, which has brought about racial differences, but it has not brought about speciation.

The more we discuss this, and the more I think this through, the more I begin to question whether speciation has anything really to do with fitness for purpose.  Speciation is first and foremost a barrier to sexual reproduction, and not of itself an adaptation to the physical environment.  It is a means of preventing genes from one population from leaking into the gene pool of another population.

Is this barrier merely a by product of extreme racial/breed divergence, or it some separate mechanism to do with genetic competition through a form of genetic branding (in the way corporations brand themselves as a way of giving themselves an identity and distinguishing themselves from their competition).  If it were merely a consequence of extreme racial/breed divergence, should not a lesser degree degree of racial separation begin to impose partial barriers to sexual reproduction?  Is there any evidence for such a partial barrier to exist between human races, or breeds of dogs?

Certainly, the physiological differences that can exist between races/breeds are substantial enough, and sometimes even greater than might exist between two species.  I am not saying that physiological differences caused by environmental adaptations do not often go hand in hand with speciation, but that would be because animals that live in different environmental niches will often be sufficiently physically isolated from each other (even if not today, then probably at some time in the past) to allow speciation to occur; but is speciation merely a product of that adaptation process, or a parallel mechanism?


quote:

Of course all that is just rationalisation of my original standpoint - I don't really know which of us is right (if either!) but at the very least you have convinced me that the there are a lot of possible mechanisms that I hadn't previously considered [:)]



Indeed, neither of us can know the real truth (nor in fact do most of the experts – but they probably have a little more information to work with than us), but it has been a useful exercise even for me to challenge my own ideas, and have to think them through to their logical conclusions.

*

another_someone

  • Guest
Re: Humans & natural selection
« Reply #25 on: 31/10/2005 23:40:55 »
quote:
Originally posted by Simmer

A steady rate of mutation can also explain phenomena like coelacanths and other long lived species - a mutation doesn't persist unless it offers some advantage, or at least no disadvantage.  In a well adapted creature in a stable environment most mutations would be less successful than the normal population and eventually be bred out.

Steady mutation rates can also explain the explosion of speciation after a mass extinction.  A regularly occuring mutation that let a well adapted nut-eating bird become a poorly adapted seed eating bird would normally be a disadvantage and be bred out every time it cropped up, unless all the well adapted seed eaters were dead and there was a niche for these mutants to survive in and become adapted to.



Sorry about coming back to this separately, I wanted to thank about this a little bit longer.

In some ways, I don't necessarily disagree with you, and in some ways we are not necessarily saying such very different things.

What you and I are both saying is that, by one mechanism or another, there must be a variability in the number of mutations that survive.  Whichever process we use, variation in the occurrence of initial mutants, or variation in survival rates of mutants, the effect is the same, that the rate of mutation surviving in the history of a species (the species and its ancestor species) will differ at different times.

Where we do have a difference of opinion is in your notion of the sole criteria that a mutation will fail is if it offers no survival advantage.  A peacock with a less elaborate tail will certainly be a peacock better able to survive, and yet if a peacock were born that were to lack its splendid tail, the mutation will die out, not because it is less able to survive, but because it is less able to find a mate.  Peahens are looking for a particular brand identity associated with a peacock, and this means that a feature which is inherently (from the purely survival perspective) inefficient will continue to flourish despite its inefficiency.

Where you would expect a peacock mutant who is born without the elaborate tail feathers to survive is where the environmental stress upon the peacock population is so great that the survival advantage begins to outweigh the mating disadvantage.

The other situation where you might expects such a mutant to survive is where there were so many mutants around as to create a shortage of mainstream 'branded' peacocks, so the peahens are obliged to accept second best.

It matters not whether there is an increase in the rate of mutation, or a reduction in the number of 'branded' peacocks, or some combination of the two; what matters is the percentage of mutants in the population has increased sufficiently as to make it difficult for the peahens to continue to conserve the old species by selecting the highest quality 'branded' peacock.

Because we are talking about a change in ratio, it again is important that we be dealing with a small isolated population, where a relatively few individuals could come to represent a large shift in percentage terms.  Again, this would be consistent with what, as far as I can ascertain, is what we see in the fossil records, that rather than one species simply mutating en masse into a new species, we see a a child species created from the parent, and the two live side by side, and in some cases the parent species will later die off (possibly having been out-competed by its child), leaving the child species to succeed it.

I would then make a further speculation.  I would suggest that mutation would not only affect superficial aspects, such as the tail of a peacock, but would probably have a wide range of impacts upon the mutant individual (chromosome damage usually has many diverse consequences).  This mutant group, contrary to traditional doctrine, far from improving the ability of the species to survive, will initially actually have a lower survival rate than the parent species, but will survive because it is isolated from its parent population, and so lacks competition with the parent species (and possibly has few other competitors within its isolated environment).  At this time, it may in fact be that these mutants are not even a distinct species, since, if the opportunity arose, they would still be able to mate with members of their parent species.

What I would speculate would then happen is that, generation upon generation, this mutant version of the species will weed out its weaklings, and begin to find novel solutions to overcome the disadvantage that the mutation brought it.  In doing so, it will create a new genome that is as successful as its parent species, but is distinctly different to its parent species.  It is only after this rapid rebuilding of a fully functional genome from the damaged genome has happened that we can then talk about a new species being in existence.

Thus, the new species has come about, not because the mutation created advantages for the individuals, but because the disadvantages that the mutation created forced the isolated population to create novel solutions to their disadvantage, until ultimately they not only overcome their disadvantage, but actually turn those novel solutions into an advantage.

Once the newly formed isolated species is formed, if it then manages to break out of its isolation, it will then possibly (depending upon the niche it created for itself while in isolation) start to compete with its parent population.

*

Offline Simmer

  • Sr. Member
  • ****
  • 229
    • View Profile
Re: Humans & natural selection
« Reply #26 on: 09/11/2005 08:52:07 »
As you say we don't disagree about everything! [:)]  

You certainly come up with some interesting takes on the evolutionary process, the idea that a disadvantageous mutation could force a subspecies to out-compete the general population is a new one to me.  Humans are curiously physically weak for members of the ape family, I wonder if that might be an example of what you are suggesting?  Our larger brains simply an adaption to our feebler biceps! [:0]

Where we do differ is on the mechanism for mutation selection.  AIUI you think that isolation of a section of the population and subsequent speciation is the principal mechanism whereas I believe that gradual changes in the mainstream population are more usual.  

That doesn't mean I don't think speciation occurs in isolated populations, obviously it does, just that this is not the most common mechanism for change.
 

*

Offline Thondar

  • Jr. Member
  • **
  • 14
    • View Profile
Re: Humans & natural selection
« Reply #27 on: 09/11/2005 17:38:42 »
I think that the human kind has been in this planet for just a shot time, that our evolution cannot be mesured in some kind of a different specie, our differences depends on groups, and groups is the thing I think is the key for our survival in the long terms.

Music should strike fire from the heart of man, and bring tears from the eyes of woman.  LVB
Music should strike fire from the heart of man, and bring tears from the eyes of woman.  LVB

*

another_someone

  • Guest
Re: Humans & natural selection
« Reply #28 on: 09/11/2005 21:45:15 »
quote:
Originally posted by Simmer

You certainly come up with some interesting takes on the evolutionary process, the idea that a disadvantageous mutation could force a subspecies to out-compete the general population is a new one to me.  Humans are curiously physically weak for members of the ape family, I wonder if that might be an example of what you are suggesting?  Our larger brains simply an adaption to our feebler biceps! [:0]



OK, I suppose I should have explained my thought processes a bit more.

The concept was something I only thought about very recently, as I was looking into the background of our own discussions here.

I came to the idea (and it is speculation) upon the realisation that chimpanzees and humans have different numbers of chromosomes.  Maybe this should not have been so shocking to me, since I had long known that dogs and humans differed in the number of chromosomes they had, but it brought it home to me to learn that chimpanzees had 24 pairs against the 23 pairs humans have.

Firstly, one cannot gain or lose an extra pair of chromosomes gradually, you either have them or you do not.  From what I have read, it seems that some researchers believe that chromosome 2 in the human genome was a fusion of two separate chromosomes in our common ancestors.  This is not the only difference between the chimp and human genome, but it is clearly the most dramatic, since it must be regarded as a quantum jump, not something that could happen by gradual shift.

Beyond the fact that you cannot gradually remove a chromosome, much less gradually fuse two chromosomes; I find it difficult to believe that a major change (almost a trauma) such as increasing or decreasing the number of chromosomes in a genome will ever initially be advantageous .  It seems to me like taking a 6 cylinder car engine, and removing two cylinders, there are many good 4 cylinder engines around, but they are designed to work with 4 cylinders (at very least the ignition sequence and timing has to take account of the number of cylinders), and are not merely 6 cylinder engines with two cylinders casually removed.  If one looks at the kind of situations where we do have those kind of dramatic changes in the human genome (although clearly different, but similar in scale, downs syndrome), they do tend to harm rather than help the survival of the afflicted individual.  If you can show me a situation where such large changes are not deleterious, then I may think differently about it.

Going from that situation, I began to ask myself if, going back to the car engine analogy, we had two cylinders drop off, we could just about limp on (but at a clear disadvantage), until we started to redesign the other parts of the engine to take account of the loss of two cylinders.

Genetic mutations are not as simple as growing another arm, reducing bone mass, increasing brain size, etc.  When a change happens in the genome, the first thing that will happen is changes in the proteins being produces in the body (changes in quantity, and maybe changes in shape).  Some of this may end up affecting large scale visible functions, but many others may be much less obvious in nature.  The trouble is that the body of an established organism will be based upon a long standing set of balanced interactions, relying on certain amounts of various proteins of a particular shape being produced.  When that balance is upset, one would imagine that the whole system gets out of balance, and if (for instance) the protein is supposed to match the shape of a particular receptor, then changing the shape of the protein will alter its fit with the receptor, and thus reduce its efficiency.  If, in subsequent generations, the balance was re-established (and the shape of any dependent receptors changed to reflect the new shape of the protein), then the efficiency of the organism would be re-established, but in a way that could not be hybridised with its parent species (since, now, both the protein and its receptor would have changed, and a hybrid inhering different proteins and receptors would be at an automatic disadvantage).

I realise that the above is a gross simplification, and I have no doubt that any competent cell biologist will shoot it so full of holes that it would sink in an instant, but it is the best of my limited understanding of the matter.

I also realise, that while it is clear that somewhere in the 5 million years since humans and other great apes diverged in evolution, and there was one instant where a change in the number of chromosomes in the genome occurred, there must also have been many other changes of species where the change in the genome was not so dramatic, and you could still put forward an argument that those cases might have happened more gradually (but that would require that we have two different mechanisms, to which I would bring forward Occam's razor).

quote:

Where we do differ is on the mechanism for mutation selection.  AIUI you think that isolation of a section of the population and subsequent speciation is the principal mechanism whereas I believe that gradual changes in the mainstream population are more usual.  

That doesn't mean I don't think speciation occurs in isolated populations, obviously it does, just that this is not the most common mechanism for change.



I'm afraid I don't know enough about all the variety of different species that have occurred in the past to be certain that it has never happened that a species has gradually created a new species (as I have indicated, the other problem is proving that two different skeletons one digs up are two distinct species, or just different breeds of the same species).

My own belief is that sexual reproduction is such a conservative force as to make this unlikely.  In bacteria, where all reproduction is asexual, then this is likely, but I don't believe it is likely in higher organisms.

Beyond that general belief, is the fact that the few points of speciation in human history that I am aware of do not seem to have occurred that way.  If one were to expect an entire species to drift from being one species to being another species, then one should see in the archaeological record that the parent and child species never overlap, since the whole species is moving forward together.  This clearly does not seem to be the case with Homo Heidelburensis and Homo Sapiens overlapped by at least 50,000 years (maybe as much as 100,000 years).  Nor would it explain how the offshoot of Homo Neanderthensis split off from the group.  It is clear that some  Homo Heidelburensis at one stage become  Homo Neanderthensis, and some time later, another group became Homo Sapiens, but it was not a case of the whole population moving together.  Of course, there is nothing in the fossil records that is ever certain, and it may one day prove to be the case that we were not descended from Homo Heidelburensis, but from some small group of proto-humans that do not yet appear on the fossil records, and that never actually overlapped with their descendent species; but that is not what presently appears to be on the records.

If one accepts that only some of the members of   Homo Heidelburensis split off to form Homo Sapiens, it does not prove how large a group that 'some' was, only that it was not the whole species.  For other reasons, most of which I think I have outlined in earlier messages (i.e. The need to overcome the conservatism of sexual reproduction), I think that group must have been very small, but at very least, it must have been less than the whole population.

*

Offline Simmer

  • Sr. Member
  • ****
  • 229
    • View Profile
Re: Humans & natural selection
« Reply #29 on: 09/11/2005 22:11:45 »
quote:
Originally posted by Thondar

 our differences depends on groups, and groups is the thing I think is the key for our survival in the long terms.



Hi Thondar

Not sure what you mean by "groups" in this context.  Populations geographically isolated from one another?
 

*

Offline DrN

  • Hero Member
  • *****
  • 815
    • View Profile
Re: Humans & natural selection
« Reply #30 on: 09/11/2005 22:53:32 »
This was a very interesting thread! I'm sorry if this has been mentioned, I may have missed something in all that, but I though speciation was generally a result of separation? whether this is physical - a mountain or river for example, or social - the result of a mutation that makes a group of individuals more likely to seek each other out over the rest of the 'normal' population. in the hope of not offending anyone, people with mutations that cause dwarfism may feel more comfortable with others like them, so eventually humans will separate into two populations, those with the 'small' genes and those with 'tall' genes. perhaps this is how several hominid species evolved in the same localisation into their separate species?

*

Offline Simmer

  • Sr. Member
  • ****
  • 229
    • View Profile
Re: Humans & natural selection
« Reply #31 on: 09/11/2005 23:33:31 »
quote:
Originally posted by another_someone


Firstly, one cannot gain or lose an extra pair of chromosomes gradually, you either have them or you do not.  From what I have read, it seems that some researchers believe that chromosome 2 in the human genome was a fusion of two separate chromosomes in our common ancestors.  This is not the only difference between the chimp and human genome, but it is clearly the most dramatic, since it must be regarded as a quantum jump, not something that could happen by gradual shift.


Of course we don't know how many chromosomes Homo Heidelburensis or Homo Neanderthensis had, nor indeed how many the common ancestor we presumabley share with chimps had.  However, I agree it's a big and probably initially disadvantageous change that doesn't appear to fit well with a "gradual accumulation of mutations" model.  But, as you youself point out, such things happen frequently to this day, most often in Down's syndrome sufferers at present. A frequent disadvantageous change may eventually coincide with another change that makes it viable.

Incidentally, people with Down's syndrome often have impaired fertility but can successfully breed with both fellow sufferers and the general population, so speciation has not occured despite the considerable genetic difference of an extra chromosome.

quote:
I also realise, that while it is clear that somewhere in the 5 million years since humans and other great apes diverged in evolution, and there was one instant where a change in the number of chromosomes in the genome occurred, there must also have been many other changes of species where the change in the genome was not so dramatic, and you could still put forward an argument that those cases might have happened more gradually (but that would require that we have two different mechanisms, to which I would bring forward Occam's razor).


Don't you shake your Occam's razor at me! [:)]  Normally I would agree but in this case we are not talking about two different processes, just the same process, mutation and selection, in different cirucmstances.  

quote:
If one were to expect an entire species to drift from being one species to being another species, then one should see in the archaeological record that the parent and child species never overlap, since the whole species is moving forward together.  This clearly does not seem to be the case with Homo Heidelburensis and Homo Sapiens overlapped by at least 50,000 years (maybe as much as 100,000 years).  Nor would it explain how the offshoot of Homo Neanderthensis split off from the group.  It is clear that some  Homo Heidelburensis at one stage become  Homo Neanderthensis, and some time later, another group became Homo Sapiens, but it was not a case of the whole population moving together.


Quite true; the coexistance of these species shows that speciation has occured between population subgroups as you are contending.  My case is harder to prove because, in the nature of things, the changes are more subtle than the supplanting of one species by another.  

However homo sapiens (both neanderthal and sapiens) were very different from their apparent common ancestor, so different that a large number of genetic changes must have been involved in the creation of both species.  Is it likely that at each step an isolated subgroup evolved, adapted and then supplanted the main population, over and over again in the few tens of thousand of years between the first sapiens fossils and the present day?  And how is it that these subgroups were safely isolated during the adaptive process but had no difficulty in accessing the general population when supplanting time came? [:)]

 

*

another_someone

  • Guest
Re: Humans & natural selection
« Reply #32 on: 10/11/2005 00:44:15 »
quote:
Originally posted by Thondar

I think that the human kind has been in this planet for just a shot time, that our evolution cannot be mesured in some kind of a different specie, our differences depends on groups, and groups is the thing I think is the key for our survival in the long terms.



In one sense, you do have a point, that human society has evolved far faster than the human animal.  Since societies may be regarded as reproducing asexually rather than sexually, the concept of speciation does not apply to them.

Yes, it is true that we have been on this planet for a relatively short period of time, probably a mere 150, 000 years, which is very short in comparison 350 million years that the Coelacanths  have survived; but then, Neanderthal man survived for a span of only 200,000 years before perishing.  The interesting question is what the final verdict will be on Homo floresiensis – how long did it live, and from whence did it spring, and was it actually a distinct species.

How long it takes for a new species to be born is basically one of the two differences of opinion that I and Simmer are discussing, the other being whether an entire species can ever convert to becoming a new species en masse.  I think we do agree that if an entire species were to change en masse, it would take a very long time, if only because of the time needed to propagate the change through the population (excepting if the change was propagated by some other means than sexual reproduction, e.g. viral infection).

*

another_someone

  • Guest
Re: Humans & natural selection
« Reply #33 on: 10/11/2005 03:38:58 »
quote:
Originally posted by Simmer

Incidentally, people with Down's syndrome often have impaired fertility but can successfully breed with both fellow sufferers and the general population, so speciation has not occured despite the considerable genetic difference of an extra chromosome.



Indeed, that is my whole point.  If the initial mutant were unable to breed with their normal counterparts, then the mutation would not survive.  It is necessary that the mutation happen within the original species, but my speculation was that it was the subsequent rapid adjustments to the genome that are made as the descendents selectively breed in order to compensate for the problems caused by the initial mutation that actually create the new species.  The new species would only be several generations after the initial mutation.

quote:


However homo sapiens (both neanderthal and sapiens) were very different from their apparent common ancestor, so different that a large number of genetic changes must have been involved in the creation of both species.  Is it likely that at each step an isolated subgroup evolved, adapted and then supplanted the main population, over and over again in the few tens of thousand of years between the first sapiens fossils and the present day?  And how is it that these subgroups were safely isolated during the adaptive process but had no difficulty in accessing the general population when supplanting time came? [:)]



OK, I will try to conjecture a hypothetical story of what might have happened.

Now children, are we sitting comfortably, then I shall begin [:)]

Once upon a time, many years ago, in a forest far away, there lived a tribe of apes.  These apes were lived near a big river, and would sometimes go there to drink water, but otherwise would stay away from the river.

Most apes don't like to swim, and humans are rather unusual in that respect, and this has lead to the rise of the aquatic ape theory of human evolution.  Anyway, back to the story.

Within in this tribe was born a young male.  The male was a sickly child, it had a genetic abnormality, but its mother nursed it, as mothers do, and it survived.

One day the river flooded, and the forest in which the tribe of apes was flooded.  The tribe all rushed to the tops of the trees, even the sickly one was helped by its mother up into the trees.  But the torrents of water became so powerful that many of the trees were felled by the water, and the apes that were up in the trees were either drowned or swept out to sea.  The tree on which our sickly mutant was sheltering, with a number of others, came down.  Many of those on the tree fell off the tree as it came down, or soon after, but our sickly adolescent and two females managed to cling to the tree, and were swept along with the current, out to sea.  After many days clinging to the tree, they finally found themselves washed up on a beach.  It was an alien place, without any big trees to climb, but it was at least dry land (well, at least it was land, maybe not so dry).

They explored timidly their new home, and found some strange fruits and berries.  Not what they were used to, but it would do.  They still lacked protein (not all apes are vegetarian: chimps do eat some meat).  They were not very comfortable on the alien beach, but they were no more comfortable in the alien hinterland, so initially they stayed around the beach area where they were washed up.  Then, as they were playing around in frustration on the beach, and throwing things around, they picked up a shellfish and threw it onto the rocks, and its shell smashed.  They scooped out the insides, and ate it.  It tasted strange, but everything was strange, and it was at least nourishment.  So they learnt to scavenge around the water front around the high tide mark.

So here were two females and a male, alone on an island.  The male, back home, would have been no alpha, and no female would have even dreamt, except maybe in their most horrid nightmare, to have such a male as their consort; but here was their nightmare, and in a land where there were no other males, he was the alpha male.

As the three young apes did what came naturally to young apes, even mutant young apes, the females suffered many miscarriages, and had many deformed offspring, but some of the survived, and some grew up.  As they grew up, they would mate and have more offspring, and gradually, the offspring became stronger and stronger as some of the more deleterious genes were bred out of the population, but they still had a lot of strange deformities.  Some of the offspring were born with flat, and feet, feet that back in the forest would have been useless for climbing trees, but here actually proved quite adept at running along beaches.  Some of the youngsters were born with very little hair, and they could sometimes find the hot days without any shade unbearable, and would sometimes rush into the water to cool off (again, shades of the aquatic ape theory – I'm not trying to say this was what happened, only this is one way it might have happened, although they claim that the lack of hair was an adaptation of swimming, and not the cause of it).

There was ample space on the island for the burgeoning new tribe of apes, and since their were no predators to threaten them, there was very little tribal cohesion, and very little tribal violence, just a benevolent anarchy in their 'garden of Eden'.  In this state of anarchy, every male could be an alpha male of his own corner of the island if he chose.  In this state, a great deal of genetic diversity continued to develop, but it could not last.  As the population grew, resources became scarcer, and the biggest bullies on the island were starting to become alphas.  The females started to feel they needed the protection of the strongest males, and so became more selective about whom they chose as a mate.  As this continued to happen, the genetic diversity began to reduce, and the diversity that had been a part of the tribe started to converge towards a new definitive genome for a new species.

From fairly early on, from when the first of these new apes started to go near the water, every once in a while, one of them would get swept out to sea.  The poor animal would usually drown, but sometimes would get beached, either back on the island, or another island, or on the mainland.  The tribe quickly learnt where the danger spots were on the island, and mostly they avoided those areas, and it was rare for one of them to be swept away.  As the population on the island grew, and the resources on the island became ever scarcer, the population would have to venture into ever more dangerous areas to collect food, and ever more of them would be swept out to sea.  As more of these island apes were swept out, so more of them found themselves beached on the mainland, until a sizeable colony started to develop along the beach front on the mainland.  These apes would not venture into the forests, where there were lots of dangerous animals, and where they could not escape by climbing trees as their ancestors had done.  They stayed in the open, where they could see what was around them, and near the sea, where they could eat the shellfish they had become used to eating.

I realise there are many problems with the above scenario, at least if one were to try and generalise from it.  For one thing, it anthropomorphises far too much, and while this may be plausible for a fairly intelligent ape, it does not explain how a dumb snail might speciate, and they too can speciate.   But the pressures on a snail may well be similar, even if the thought processes may not necessarily be there.

It also relies too much on looking at the aquatic ape hypothesis as a model for human evolution, and as you say, we must look at many instances of change, and they could not all lead to the same end result.  On the other hand, the flood could be a landslide, a fire that chases the animals out of the forest, or any one of a number of natural disasters.  The island could be a metaphor for an isolated valley in the mountains, an oasis in the desert, or anywhere that will cut them off from their familiar surroundings, and will not have significant numbers of predators (the fact that they are aliens in the environment will often mean that no species has yet developed a taste or ability to predate them in that environment).

This is not the kind of scenario one would expect to happen every day, but it is easily the kind of this that sounds plausible to happen once a century, let alone once every 100,000 years.

*

Offline Thondar

  • Jr. Member
  • **
  • 14
    • View Profile
Re: Humans & natural selection
« Reply #34 on: 10/11/2005 08:33:46 »
quote:
Originally posted by Simmer

quote:
Originally posted by Thondar

 our differences depends on groups, and groups is the thing I think is the key for our survival in the long terms.



Hi Thondar

Not sure what you mean by "groups" in this context.  Populations geographically isolated from one another?



hi Simmer

I was talking about humans being the kind of animals that live in base of a group, we are a social specie. What's not clear to me its the thing of "the evolution of our specie" or its just the "line" we are talking.
Like another_someone said, Neanderthal man endured only about  200,000 years, but we could consider then that is the same line we are passing through the years and we are the human kind of the momment like they were in their time. Why am I questioning this? because I believe that our evolution is merging the physical and intellectual kind, we are not anymore the ones we were about going out and hunt, sleeping in complete darkness just lighted by the moon light with an eye open just in case another animal is trying to eat one of our babies. We are doing the same theory but with other methods, like working and bringing money to our properly acommodated homes, defending our families with strategy in general life rather than with a weapon under our pillow. I think it could fit into another cathegory of human being with difference of a few thousand years. And because of that our physical evolution is molding how we look in this days affected by our surrounding enviroment which like HarryPalmer said, is altered by ourselves.

Music should strike fire from the heart of man, and bring tears from the eyes of woman.  LVB
Music should strike fire from the heart of man, and bring tears from the eyes of woman.  LVB

*

another_someone

  • Guest
Re: Humans & natural selection
« Reply #35 on: 10/11/2005 18:02:59 »
quote:
Originally posted by Thondar

I believe that our evolution is merging the physical and intellectual kind, we are not anymore the ones we were about going out and hunt, sleeping in complete darkness just lighted by the moon light with an eye open just in case another animal is trying to eat one of our babies. We are doing the same theory but with other methods, like working and bringing money to our properly acommodated homes, defending our families with strategy in general life rather than with a weapon under our pillow. I think it could fit into another cathegory of human being with difference of a few thousand years. And because of that our physical evolution is molding how we look in this days affected by our surrounding enviroment which like HarryPalmer said, is altered by ourselves.




As I said earlier, you are right to say that our society is evolving, but as I said, that is different the evolution of our species.

It is true that our environment is influencing our physical evolution, and are environment includes substantially our physical environment.  The question was one of whether we create a new species, rather than just a new breed within our existing species.

Like all definitions, the real world is never as clear cut as our definitions make it appear to be, but the definition of a species is essentially that two individuals from two species are incapable of interbreeding.  It is seems clear that at this time there is nothing in the changes that society imposes upon us that makes interbreeding with our earlier self impossible, excepting the fact that we don;t live in the same time.  When Europeans first made contact with the natives of the Americas and Australia, there had not been any contact with those people for at least 10,000 years, and yet there was no problem with these different peoples interbreeding.  We must conclude from this that the peoples of the 16th and 18th centuries would still have been capable of interbreeding with their ancestors of 10,000 years previously.  They may have been of a different race (i.e. a different breed), but not a different species.

In a different domain to this, I did put forward a very different conjecture about the future evolution of human society (and I stress, this applies to the society, not the human animal).

One of the things we do observe is that over time, particularly since the advent of the industrial revolution, and accelerating ever since, the various functions that previously were performed by human animals are ever more being performed by machines.  In the computer age, these are not even simply physical tasks, but intellectual tasks, tasks that require an element of judgement.

In these same societies, we have seen a gradual decline in the birth rate.  Initially, the decline in mortality exceeded the decline in birth rate, and so the populations actually increased significantly.  More recently, although the decline in mortality continues, the decline in birth rate has started to overtake the decline in mortality, and so we are facing the possibility of a decline in human population in these countries (at least if the deficit is not made up for by immigration – but immigration will only work so long as there are other countries which have not followed the industrialised world in this trend of reducing population).

The logical extrapolation of this is that over time, although human society will still be the society that humans have created, it will ever more in practice be a society of machines taking the functions that previously were performed by humans.

*

Offline Simmer

  • Sr. Member
  • ****
  • 229
    • View Profile
Re: Humans & natural selection
« Reply #36 on: 10/11/2005 22:22:12 »
quote:
Originally posted by fishytails

This was a very interesting thread! I'm sorry if this has been mentioned, I may have missed something in all that, but I though speciation was generally a result of separation?


Well I've certainly found it interesting and a bit challenging - not for the first time I get the impression that there are people on this forum who know what they are talking about; very unfair in my opinion! [:)]  

I suspect that you are right that the expert concensus is that speciation requires separation. I am arguing another mechanism partly in the spirit of debate and partly because of my extreme reluctance to admit I might be wrong!

quote:
...whether this is physical - a mountain or river for example, or social - the result of a mutation that makes a group of individuals more likely to seek each other out over the rest of the 'normal' population. in the hope of not offending anyone, people with mutations that cause dwarfism may feel more comfortable with others like them, so eventually humans will separate into two populations, those with the 'small' genes and those with 'tall' genes. perhaps this is how several hominid species evolved in the same localisation into their separate species?


That's an interesting point, the required separation doesn't have to be geographic - I can even think of a relatively modern example; the so-called "Bushmen" in southern Africa, a small people perhaps related to the pygmies of central Africa, who were considered and treated as wild animals by other, taller races in the region until very recently.

Of course this is a further prop for the tottering intellectual edifice of speciation through isolated subgroups - but I forgive you! [:D]
 

*

Offline Simmer

  • Sr. Member
  • ****
  • 229
    • View Profile
Re: Humans & natural selection
« Reply #37 on: 10/11/2005 23:27:13 »
quote:
Originally posted by Thondar

 I believe that our evolution is merging the physical and intellectual kind, we are not anymore the ones we were about going out and hunt, sleeping in complete darkness just lighted by the moon light with an eye open just in case another animal is trying to eat one of our babies. We are doing the same theory but with other methods, like working and bringing money to our properly acommodated homes, defending our families with strategy in general life rather than with a weapon under our pillow. I think it could fit into another cathegory of human being with difference of a few thousand years. And because of that our physical evolution is molding how we look in this days affected by our surrounding enviroment which like HarryPalmer said, is altered by ourselves.



I think I see what you mean, humanity is partly (or even mostly) human society - developments in that society could be considered to be a form of evolution for the species rather than the individual.  Faster than the tedious genetic kind too!

I also liked the irony in your point that in shaping our environment we may end up changing ourselves to match it! [:)]  

Of course another frightening consideration along the same lines is the prospect of genetic surgery, changing our genome directly without any evolutionary process at all! [:0]  

Well, they do say that two heads are better than one! [:D]
 

*

Offline Simmer

  • Sr. Member
  • ****
  • 229
    • View Profile
Re: Humans & natural selection
« Reply #38 on: 10/11/2005 23:54:15 »
quote:
Originally posted by another_someone

 
Now children, are we sitting comfortably, then I shall begin [:)]

Once upon a time.......

This is not the kind of scenario one would expect to happen every day, but it is easily the kind of this that sounds plausible to happen once a century, let alone once every 100,000 years.



Loved the story, a bit sad in the middle but with a happy ending.   The aquatic ape bit was good too, one of my favourite speculations [:)]

Still not convinced though ("Oh no!" I hear you groan [:)]). I don't have a problem with small groups washed away in trees and speciating over a relatively short period - what I think would take a long time is for that subgroup (assuming it becamse superior in some way) to supplant the unchanged population. Look at neanderthal and humans, living side by side for ten thousand years.  And this would have to happen not once but surely many times to get from the predecessor species to full blown human?

I still think that, where possible, breeding is a faster way to spread new genetic information than war.  Call me an old hippy if you like, but all you need is love! [:D]

 

*

another_someone

  • Guest
Re: Humans & natural selection
« Reply #39 on: 11/11/2005 02:36:23 »
quote:
Originally posted by Simmer

Still not convinced though ("Oh no!" I hear you groan [:)]).



You don't hear me groaning at all.  Now, if you'd said you agreed with everything I said, I'd have to go back and see which bit I got wrong. [:)]

quote:

 I don't have a problem with small groups washed away in trees and speciating over a relatively short period - what I think would take a long time is for that subgroup (assuming it becamse superior in some way) to supplant the unchanged population. Look at neanderthal and humans, living side by side for ten thousand years.  And this would have to happen not once but surely many times to get from the predecessor species to full blown human?



Minor correction – neanderthals and humans lived along side each other for more like a hundred thousand years, not a mere ten thousand.

Beyond that, I don't think there is any disagreement.  I never said that the process of one species supplanting another was a fast process, only that the period of time in which the original split happened was a relatively short period of time.  Once that split has happened, yes, it can take a hundred thousand years or more, or maybe never, for one species to out-compete another.  Even just the enormous range that some species cover would make it difficult for the new species (unless it was capable of flight) to migrate across the six continents in less than a few tens of thousands of years.

I am not sure what you mean by the process having to happen several times to get from  the predecessor species to full blown human.  The division from ape to proto-human happened first about five million years ago, and the final step, from  Homo Heidelbergensis to modern human was probably around a hundred and fifty thousand years ago.  There were many steps between the last ape and the modern human, but the step from  Homo Heidelbergensis to modern human was the last of those steps (with, if what I read is correect) neanderthal man being a side branch along the way.

quote:

I still think that, where possible, breeding is a faster way to spread new genetic information than war.  Call me an old hippy if you like, but all you need is love! [:D]



Mostly, it is not war.  We don't know exactly why humans supplanted, first Homo Heidelbergensis, and then neanderthal man, but it is more likely that we first out bred them, and then starved them out, than that we actually deliberately set about to kill them.  Even today, I suspect there are far more animals in the world who die because humans have destroyed their habitat and their food source than are actually hunted by humans.

If you take my example story above, you will see that the modified apes, when they return to the mainland, start to populate a very different environment from their ancestors, and so would not be looking to hunt their ancestors, or even, initially, be in direct competition with them.  It would only be later, as the population of the new species grows, and they are forced to further extend their range of habitat, that you might find they start coming into direct competition with their ancestor species.


*

Offline AlphBravo

  • Full Member
  • ***
  • 65
    • View Profile
Re: Humans & natural selection
« Reply #40 on: 12/11/2005 12:30:57 »
Or the population adapts to the environment, like smaller folk in the forests and mountains.
But there is usually a coalescing of the gene pool by trade and warfare etc.
Maybe it is skewed in a modern setting
 

*

another_someone

  • Guest
Re: Humans & natural selection
« Reply #41 on: 12/11/2005 16:45:29 »
quote:
Originally posted by AlphBravo
Or the population adapts to the environment, like smaller folk in the forests and mountains.



I would guess that first the population will try and maximise its use of the environment where it is most capable, and it is only when it no longer has capacity to expand its natural environment (at least, locally) that it will try and expand into alien environments, and only after it starts to encroach on alien environments will it start to adapt itself to those environments.

quote:

But there is usually a coalescing of the gene pool by trade and warfare etc.
Maybe it is skewed in a modern setting



This would, I guess, depend upon the population density.  Modern humans live in a very crowded world, and so there is little room to develop isolated populations that would have significantly different gene pools.