0 Members and 1 Guest are viewing this topic.
quote:Originally posted by SimmerWe 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 
quote:Originally posted by thefunkyaquariumThe 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 
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).
quote:Originally posted by SimmerI 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.
quote:Originally posted by SimmerHowever, 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.
quote:Originally posted by daveshortsI 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...
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.
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.
quote:Originally posted by SimmerI 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! 
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.
quote:Originally posted by another_someoneTwo 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.
quote:Originally posted by UltimaNice 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.
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.
quote:Originally posted by SimmerI 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.
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. 
quote:Originally posted by UltimaThat is fairly thoughtless, get a pet! Or even better make something of your life. The tax payers 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.
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.
quote:Originally posted by another_someoneIf 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.
quote:Originally posted by SimmerFor 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?
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.
quote:Coelacanths were believed to first appear in the Carboniferous Period, about 400-350 million years ago.
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.
quote:Originally posted by another_someoneWe 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).
quote:Originally posted by SimmerIf 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.
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.
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.
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.
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 
quote:Originally posted by SimmerA 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.
quote:Originally posted by SimmerYou 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]
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.
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.
quote:Originally posted by another_someoneFirstly, 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.
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).
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.
quote:Originally posted by ThondarI 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.
quote:Originally posted by SimmerIncidentally, 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: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? 
quote:Originally posted by Simmerquote: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 ThondarNot sure what you mean by "groups" in this context. Populations geographically isolated from one another?
quote:Originally posted by ThondarI 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.
quote:Originally posted by fishytailsThis 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?
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?
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.
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.
quote:Originally posted by SimmerStill not convinced though ("Oh no!" I hear you groan ).
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?
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! 
quote:Originally posted by AlphBravoOr the population adapts to the environment, like smaller folk in the forests and mountains.
quote:But there is usually a coalescing of the gene pool by trade and warfare etc.Maybe it is skewed in a modern setting