Naked Science Forum
Life Sciences => Plant Sciences, Zoology & Evolution => Topic started by: echochartruse on 30/03/2010 18:05:15
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Natural selection Doesn't explain how a totally new speicies arises - to me. It seems to me that he is discribing a species that has altered slightly in some way, possibly through epigenetics or other to proceed where the same species of previous generations did not change, had no need to change. Where the ancestors of say, turtles an entirly different species or a variation of the same species? - appology for too many questions, just trying to understand
Can someone with knowledge of Dawin's theory please explain how a new species arises in the simplist terms?
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I understand the theory says new species arise through natural selection. It's a question of time. We are talking about time intervals that are incomprehensible from human experience.
I'm no expert in this field, but I assume what happens is that over a long enough period, related groups become incapable of interbreeding because they are prevented from interbreeding through isolation, or some physical change that makes it impossible. Then over a long period of time, their genes diverge sufficiently that interbreeding becomes impossible. At that point, you have a new species.
Are horses and donkeys different species? I tend to think they are. They can interbreed to produce a mule, but there will never be a species called "mules". Mules, are incapable of breeding.
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It seems to me that he is discribing a species that has altered slightly in some way, possibly through epigenetics or other to proceed where the same species of previous generations did not change, had no need to change.
All populations of organisms have some variety and new variations enter into the population all the time through mutation. If there is no pressure from the environment that makes one variation significantly different from another, then there will be no change in the average individual in the population over time. If something in the environment makes it so that one or two variations are significantly different (and better able to survive), then over time the average individual in a population will change accordingly.
Small changes in variation can build up over time.
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..... I assume what happens is that over a long enough period, related groups become incapable of interbreeding because they are prevented from interbreeding through isolation, or some physical change that makes it impossible. Then over a long period of time, their genes diverge sufficiently that interbreeding becomes impossible. At that point, you have a new species.
Are horses and donkeys different species? I tend to think they are. They can interbreed to produce a mule, but there will never be a species called "mules". Mules, are incapable of breeding.
what are you refering to as 'related groups' please?
when you say interbreeding are you speaking of breeding between different species?
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All populations of organisms have some variety and new variations enter into the population all the time through mutation. If there is no pressure from the environment that makes one variation significantly different from another, then there will be no change in the average individual in the population over time. If something in the environment makes it so that one or two variations are significantly different (and better able to survive), then over time the average individual in a population will change accordingly.
Small changes in variation can build up over time.
I agree that small variations do change (such as children from their parents) but I truely dont understand how a new species arises from this.
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Was it just the same species doing adaptaions to the surrounding environment? Did an entirely new species come from another species?
Essentially yes, but you shouldn't get hung up on the idea of different species. "Species" are, after all, just labels that humans put on different things.
did the kangaroo climb a tree to become a possum then decide to climb down and becoem a rock wallaby? then why didnt they all become possums?
There was once an ancestor of all these animals. Some of these (for whatever reason) spent more time in the trees - this population were then subject to the selection pressure of arborial life, and eventually became the species we now call the possum. Other populations of this ancestor species moved into other environments, and different selective pressures acted.
Survival of the fittest, why didnt they all become one species what changed some to be another species, dont they know humans are top of the evolution chain.
This is due to the fact that several different things can be the "fittest" for different ways of life in the same area - each one specialising towards a different way of life.
Humans are not special - we're not top of the evolution chain - every extant species is the pinnacle of evolution.
That's it in a nutshell.
Populations change over time. Given enough time and enough pressure (and things like the founder effect/bottleneck effect), these populations will become no longer able to breed with one another. We then call them new species.
It honestly is that simple.
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I agree that small variations do change (such as children from their parents) but I truely dont understand how a new species arises from this.
Basically it usually involves a separation of the two groups, often physically. If two groups of individuals of the same species are put in two different places, such that they don't (or don't often) meet, then over many generations the small parent-to-child changes will accumulate and eventually the two groups will no longer be able to interbreed. Does that make sense to you? In some cases the groups will be subjected to selection pressures which will mean that different characteristics are favoured (say an ability to run fast and escape predators in one case, and a long nose to get food out of the ground in another), so they'll end up looking different and with different habits, but that's not really necessary for speciation.. simple random changes over time without interaction between the groups is sufficient.
It's not complicated it's just that it typically takes quite a lot of generations.
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......... you shouldn't get hung up on the idea of different species. "Species" are, after all, just labels that humans put on different things.
Still trying to get my head around this.... what does the label 'species' refer to?
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Basically it usually involves a separation of the two groups, often physically. If two groups of individuals of the same species are put in two different places, such that they don't (or don't often) meet, then over many generations the small parent-to-child changes will accumulate and eventually the two groups will no longer be able to interbreed. Does that make sense to you? In some cases the groups will be subjected to selection pressures which will mean that different characteristics are favoured (say an ability to run fast and escape predators in one case, and a long nose to get food out of the ground in another), so they'll end up looking different and with different habits, but that's not really necessary for speciation.. simple random changes over time without interaction between the groups is sufficient.
It's not complicated it's just that it typically takes quite a lot of generations.
Am I right saying that if humans refained from travel and mixed race marriages then it is possible a new 'species' would evolve over time?
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Populations change over time. Given enough time and enough pressure (and things like the founder effect/bottleneck effect), these populations will become no longer able to breed with one another. We then call them new species.
I dont understand if they are 'no longer able to breed with one another' how are they able to survive if not able to reproduce over vast periods of time? How do they quickly find an individual they can breed with?
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Populations change over time. Given enough time and enough pressure (and things like the founder effect/bottleneck effect), these populations will become no longer able to breed with one another. We then call them new species.
I dont understand if they are 'no longer able to breed with one another' how are they able to survive if not able to reproduce over vast periods of time? How do they quickly find an individual they can breed with?
Ah, I see your confusion - I'm talking about populations, not individuals.
Yes, if human populations were separated for a sufficiently long time, with enough selection pressure, it's possibe that these populations would no longer be able to breed, and we would define them as new species.
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......... you shouldn't get hung up on the idea of different species. "Species" are, after all, just labels that humans put on different things.
Still trying to get my head around this.... what does the label 'species' refer to?
There's a few different definitions, but the broadest and most convenient is just two populations that cannot breed to have viable offspring.
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Am I right saying that if humans refained from travel and mixed race marriages then it is possible a new 'species' would evolve over time?
It's worth noting that "race" may not be the best indicator of genetic difference.
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Am I right saying that if humans refained from travel and mixed race marriages then it is possible a new 'species' would evolve over time?
It's worth noting that "race" may not be the best indicator of genetic difference.
No, No, I hope you dont think of me as racist.........
Maybe I misunderstood you.
If a population is segregated (say distance, location, whatever) and the environmental factors of each group differ, then over a long period of time, this same 'species' would not be able to breed together becasue of it. Becasue each group would develop differently? is that what you are saying?
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In very broad strokes, yes.
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There's a few different definitions, but the broadest and most convenient is just two populations that cannot breed to have viable offspring.
Wouldn't it just be: each segregated group only able to breed within their group as they evolve? I dont see how this creates a separate 'species'
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Ah! Right, "populations" is a better term.
Consider this hypothetical example.
There is a population of elephants on a big island. Gradually, sea level rises, and the island becomes two island, leaving some elephants on one, and some on the other. The food supply on one island happens to favor small elephants, other way round on the other island. Over time, the two populations will differ greatly in size.
Now, it's quite possible the two populations are genetically compatible, so they could possibly reintegrate. However, because they are now very different in size, interbreeding by natural means is impossible. Technically they are still a single species, but because of mutations, unless they somehow figure out a way to interbreed, over time they will become two different species.
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Ah! Right, "populations" is a better term.
Consider this hypothetical example.
There is a population of elephants on a big island. Gradually, sea level rises, and the island becomes two island, leaving some elephants on one, and some on the other. The food supply on one island happens to favor small elephants, other way round on the other island. Over time, the two populations will differ greatly in size.
Now, it's quite possible the two populations are genetically compatible, so they could possibly reintegrate. However, because they are now very different in size, interbreeding by natural means is impossible. Technically they are still a single species, but because of mutations, unless they somehow figure out a way to interbreed, over time they will become two different species.
Sorry this is what I have trouble with. Wouldn't they be the same species still just hybridised?
Birds for example, I never see them interbreeding, except for human influence or I haven't heard of it otherwise, but they are still the same species.
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Wouldn't it just be: each segregated group only able to breed within their group as they evolve? I dont see how this creates a separate 'species'
Perhaps a concrete (wholly fictional) example might help?
A definition of what is required for two populations of similar animals to be considered to be different species is for them to be unable to interbreed. Interbreeding allows genetic material to be shared across subsequent generations, so the two populations won't diverge significantly in their characteristics, but once this has ceased (and it is generally because the populations are moving in different areas that interbreeding stops) there is no check on the effect of random genetic changes (and where applicable differing selection pressures) causing those two groups to diverge further even if they return to living in the same environment.
Speciation is hard to pinpoint, because sometimes you could in principal get a population of animals living on one side of a mountain range, which differ sufficiently from another population on the other side to be unable to interbreed (perhaps one group has got much bigger than the other and the small males can't mount the large females but the small females can't carry the large offspring of the large males), but yet a third group of medium sized animals living in the mountains could exist which can interbreed with both groups. If the medium sized animals were killed off by a few very harsh winters, the large and small populations would then become seperate species, and their future evolutionary pathways wouldn't be influenced by interbreeding with their cousins from over the hills. But if the population of humans on either side of the mountains drove both groups further up into the hills so they met and interbred more often with the medium sized animals, then those animals which had the widest choice of mates would tend to do well, which would work in favour of the medium sized animals and against the extreme differences which might prevent successful offspring of mixing.
I think this explanation would make more sense if it weren't so late at night here.. apologies if it's incomprehensible.
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Hmm, preempted by Geezer's better explanation, but I post anyhow.
Birds for example, I never see them interbreeding, except for human influence or I haven't heard of it otherwise, but they are still the same species.
Sorry?? I'm not sure if this is what you meant. If it is - there are many, many different species of birds! "Birds" is a very general class like "mammals" or "fish". If this is news to you I'm not surprised you're struggling with evolution, and indeed am very impressed you're trying!
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Rosy, I think my mind is blocked with the word 'species' still.
Can you give me an example in real life terms, 2 distinct unrealted 'species' interbreeding?
I still see it as hybridisation of a 'species' Sorry.
Oh so now I also understand that 'species' is not associated with just the appearance, such as birds, thanks. Which is probably why they dont interbreed, is it?
Why dont different 'species' interbreed? I suppose I should understand one thing before I ask another question.
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Why dont different 'species' interbreed? I suppose I should understand one thing before I ask another question.
Sometimes they try, but if they're sufficiently different they don't succeed. That can be for lots of reasons, one of which is that cell biology is incredibly subtle, your genes tell your cells which proteins to it can make and lots of things (the initial condition of the cell, external factors, which other genes are "switched on") will determine how much of what. That's an astonishingly fine balancing act and depends on lots of interacting systems which have to have their feedback loops just right to work at all.
When a sperm meets an egg, some of the genes from each of the mother and father (assuming they recognise each other, which in sufficiently different species they won't) are combined to make the first cell of the new individual. That cell then starts making proteins, if the balance of the proteins its genes are telling it to make are wrong, it won't survive. It will never make it to the stage of being a reproductively viable individual.
In very closely related species (like horses and donkeys) the offspring may be a pretty successful individual in terms of its own survival, but unable to breed, in other combinations the egg may just never get fertilised. In some cases, where two populations haven't interbred much and they've got quite a long way apart from each other in terms of genetics, it might be that interbreeding between the two populations is only very rarely successful, but some can survive, and if those individuals go on to breed successfully it could lead to the formation of seperate species being prevented because more breeding between groups becomes possible. It's all very smudgy round the edges. As is my brain, it's too late at night and I should be in bed! Night all.
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Rosy after I last wrote I thought for a while and became totatlly confused. Now reading your last post it has made so much more sense. I still have lots of questions but need to fully digest and filter the questions I have in hope that most are answered. thank you
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If because of some environmental influence my children were born without legs and instead grew stumps and their children and generations after generations due to the non changing environment were born the same would they would be mutants/hybrids of the same species?
So what I understand is that there has to be interbreeding between 2 or more distinct groups so distant related that you could say they are ‘separate species’ I would suppose that would mean that each group did not share, say the same ancestral mother.
With Domestic cats such as the Bengal breed it is not a specific new species only a hybrid.
I can’t think of any example of a new species that has been influenced by humans, can someone help me here. As I’m thinking if we can hybridise a species we could possibly create a new species.
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Domestic cats are a different species than their wild counterparts, as far as I know. (Dogs, however, can interbreed with wolves and therefore aren't a separate species.) Other domesticated animals or plants might be separate species from their wild counterparts as well.
Domestication is an example of humans helping an organism with certain mutations survive and continually selecting for offspring with more favorable traits for domestication. Eventually enough mutations accumulate that a new species arises.
There's also a new field called synthetic life, where the goal is the creation of life (and new species) by building single-celled organisms in a lab.
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Populations change over time. Given enough time and enough pressure (and things like the founder effect/bottleneck effect), these populations will become no longer able to breed with one another. We then call them new species.
It honestly is that simple.
After looking back over this forum, I find that I am still confused.
The word species is very confusing.
Different species/ populations cant breed together or if they do then they can not reproduce any further. But if they do and their offspring can reproduce then we call it a new species?
My interpretation of 'species' was that each group had different heritage but if we all came from the same single cell .........where did this inability to breed with each different population come into it?
A. afarensis, H. habilis, H. erectus, archaic H. sapiens, Neanderthal man and finally Cro-Magnon or modern man are all varients of the human race or are they labeled by us a different species?
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After looking back over this forum, I find that I am still confused.
The word species is very confusing.
It is! In my zoology degree we spent weeks discussing the different definitions of "species" and what the implications were.
Different species/ populations cant breed together or if they do then they can not reproduce any further. But if they do and their offspring can reproduce then we call it a new species?
I think you've pretty much got it, but lets try another example.
There's a species called A.
There are lots of groups of A, living in a field. A flood creates a river that splits A into two groups, 1 and 2.
This geographical barrier stops the movement of genes from 1 to 2 and vice versa.
Over time, the foundation effect (the fact that 1 and 2 started with slightly different genes), gene flow, mutations and natural selection (especially if 1 and 2 have different pressures - maybe there's not much food on 1's side, but snakes on 2's side) will alter the DNA of each population.
Given enough generations, it's possible that 1 and 2 will no longer be able to have viable offspring (or may refuse to mate, as maybe the ladies of population 2 are very picky, and will only mate with the males who are best at killing snakes).
By the broadest of definitions, we would now say that 1 and 2 are different species.
My interpretation of 'species' was that each group had different heritage but if we all came from the same single cell .........where did this inability to breed with each different population come into it?
Not quite the right interpretation of species. All extant species share some heritage, with varying degrees of separation.
A. afarensis, H. habilis, H. erectus, archaic H. sapiens, Neanderthal man and finally Cro-Magnon or modern man are all varients of the human race or are they labeled by us a different species?
Good question.
The problem here is that we only have fossil data, as only one species of human is extant (so it's not like comparing wolves to dogs, or even grass to wheat). It's easiest to think of this as the "humanoid" branch of the evolutionary tree.
The evidence for each of these (A. afarensis, H. habilis, H. erectus, archaic H. sapiens,) shows morphological differences between each other - each would seem to be a branch on the tree of which modern homo sapiens sapiens is currently the only twig left.
It's worth having a look at the wikipedia page for human evolution - that gives some timelines and geographical distributions that might help.
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There have been a lot of good answers to this question so far, but I'd like to give a go at it.
First off I'd like to point out that when people are referring to differing environmental factors between separate populations of the same species, they aren't just referring to things like weather and terrain. A huge component of the "environment" is the different predators and competitors which geographically separate/genetically isolated populations may have to deal with.
As I understand it, the first component involved in the evolution of a new species, is distance or separation. A successful species tends to produce more offspring than a particular region can handle. What ends up happening, is either a predator moves into the area or the offspring migrate. Often, the migration ends up cutting off the offspring from the original genetic pool. As different species migrate, they come in contact with other species which they had never encountered before which can be either predator or competitor. This competition means that certain mutations will be favored over others, and spread throughout the local populations. When prey mutates better defense, predator then mutates better offense. Populations of the same species which are cut off from each other genetically are often also subject to vastly different predator/competitor combination's which take them down very different evolutionary paths. Eventually, the two groups are genetically incompatible and labeled a new species, but eventually often takes thousands if not millions of years.
The speed at which a host organism can evolve into a new species is a direct reflection of the lifespan of each generation. Since only a few mutations are "allowed" in each new generation, it takes a lot of generations to develop enough differences to prohibit reproduction with the "original" species, as well as the requirement that the two groups are completely isolated from each other.
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...................Eventually, the two groups are genetically incompatible and labeled a new species, but eventually often takes thousands if not millions of years.
The speed at which a host organism can evolve into a new species is a direct reflection of the lifespan of each generation. Since only a few mutations are "allowed" in each new generation, it takes a lot of generations to develop enough differences to prohibit reproduction with the "original" species, as well as the requirement that the two groups are completely isolated from each other.
So basically and not so unscientific as I once thought....Mother Nature, Father Time do have a roll to play in evolution.
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Domestic cats are a different species than their wild counterparts, as far as I know. (Dogs, however, can interbreed with wolves and therefore aren't a separate species.) Other domesticated animals or plants might be separate species from their wild counterparts as well.
I was told that separate species can't mate but here are a few that seems to have mated.
http://www.messybeast.com/genetics/hybrid-cats.htm
The Savannah Cat is a result of breeding an African Serval with a spotted domestic short hair cat.
the Characat is bred from a Caracal lynx sire and an Abyssinian domestic cat dam.see link above for more.
There's also a new field called synthetic life, where the goal is the creation of life (and new species) by building single-celled organisms in a lab.
WHY?
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After reading through this thread, I don't think the original question has been answered specifically. Darwin observed complex behavior and species/sub species differentiation due to environment ,and he described this process as 'natural selection'. He then *inferred* that this process eventually gives rise to new species. He did later work on his 'transmutation of species' again proposing that species mutate over time into new species. I have a general problem with this theory of transmutation.
So, if transmutation is true, then from a critical view, there is a rather fantastic set of events that leads to a new species. We know that species are defined by their DNA that is organized into chunks, chromosomes. The the ape to man jumped happened at some point when a single individual [ape] with 48 chromosomes, mutated to a human having 46 chromosomes. At this point, that particular individual would have no one with whom he/she could successfully mate, so there must have been two...? Adam and Eve..? But a viable population must have more than just a single set of individuals to genetically propagate, it seems to me. So there was this mutation that happened to a whol large group of apes, simultaneously..?
I just don't understand the mechanism of this most necessary mutation that would give rise to speciation.
Anyone able to help me out here?
Kevin
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After reading through this thread, I don't think the original question has been answered specifically. Darwin observed complex behavior and species/sub species differentiation due to environment ,and he described this process as 'natural selection'. He then *inferred* that this process eventually gives rise to new species. He did later work on his 'transmutation of species' again proposing that species mutate over time into new species. I have a general problem with this theory of transmutation.
So, if transmutation is true, then from a critical view, there is a rather fantastic set of events that leads to a new species. We know that species are defined by their DNA that is organized into chunks, chromosomes. The the ape to man jumped happened at some point when a single individual [ape] with 48 chromosomes, mutated to a human having 46 chromosomes. At this point, that particular individual would have no one with whom he/she could successfully mate, so there must have been two...? Adam and Eve..? But a viable population must have more than just a single set of individuals to genetically propagate, it seems to me. So there was this mutation that happened to a whol large group of apes, simultaneously..?
I just don't understand the mechanism of this most necessary mutation that would give rise to speciation.
Anyone able to help me out here?
Kevin
Let me see if I can help here.... First off, humans didn't evolve from apes, rather apes and humans have a common ancestor. So Humans didn't have to "lose" two chromosomes, it's possible that apes "gained" two chromosomes. I have had similar issues with the fantastic circumstances required for purely "random" mutations, but I feel that recent science has answered that problem. We have learned that in order for large phenotypic changes to happen, we actually don't need to have changes to the genome, we can have changes to the epigenome instead. Epigenomic changes are a direct response to environmental changes, and therefore are present in an entire local population. I believe these epigenomic changes can eventually become genomic changes, and this is likely to be the foundation for most of the genetic diversity we see on Earth today. I believe that this probably evolved ~750 million years ago, and that is why we see almost no evolution prior to ~750 million years ago and then all of a sudden thousands of new species evolving at a much faster rate.
Please see my post here for more detailed information on Epigenetics and what I feel probably happened: http://www.thenakedscientists.com/forum/index.php?topic=30685.0
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Ok so I have still some questions and have searched out some answers.
The genetics of speciation are extremely difficult to figure out. The reason for that is simple enough. Since speciation means that interbreeding is not possible, it becomes very hard to interbreed the different species an use the findings to determine the speciation genes. That is the opinion of Nitin Phadnis, a geneticist at the Fred Hutchinson Cancer Research Center in Seattle........
"What this work shows you is that speciation can happen not only because of adaptation to the external environment, but also because of adaptation to the internal genomic environment," Phadnis says.
transposable elements are jumping genes. Epigenetics can play a large roll in where abouts your genes sit in relation to your DNA. Previously Junk DNA are now considered TE transposaable elements and is thought to be responsible for our individuality among our group/species.
I have always thought 'random mutation' to be unscientific. Mutations in DNA cause disease.
However, the idea that mutations are random can be regarded as untrue if one considers the fact that not all types of mutations occur with equal probability. Rather, some occur more frequently than others because they are favored by low-level biochemical reactions. These reactions are also the main reason why mutations are an inescapable property of any system that is capable of reproduction in the real world. Mutation rates are usually very low, and biological systems go to extraordinary lengths to keep them as low as possible, mostly because many mutational effects are harmful........
Finally, still other sources of mutations are the many different types of transposable elements, which are small entities of DNA that possess a mechanism that permits them to move around within the genome. Some of these elements copy and paste themselves into new locations, while others use a cut-and-paste method. Such movements can disrupt existing gene functions (by insertion in the middle of another gene), activate dormant gene functions (by perfect excision from a gene that was switched off by an earlier insertion), or occasionally lead to the production of new genes (by pasting material from different genes together)......
Many direct and indirect methods have been developed to help estimate rates of different types of mutations in various organisms. The main difficulty in estimating rates of mutation involves the fact that DNA changes are extremely rare events and can only be detected on a background of identical DNA.
So could the environment cause the shuffling of genes within our DNA (DNA being the store room for information)as well as switching genes on and off and this leads to variations and adaptation, which makes more scense to me than 'random' mutation.
The thrust of this presentation has been to point out how the discovery of transposable elements as agents of genome restructuring has brought the question
of evolutionary change into the realm of cell biology, where regulation and biological information
processing are major factors. We are entering the next century with an increasingly computational view of cells and how they make important decisions. The argument here is that evolutionary change is not exempt from this new perspective. Evidence from a variety of systems indicates that transposable elements can interact in a molecularly plausible way with signal transduction networks, the key information processing entities in the cell. Biological feedback can play a critical role in genomic responses to emergencies (McClintock, 1984). Thus, organisms have a farmore powerful evolutionary potential to generate integrated genomic networks and ensure the survival of
their descendants than predicted by current theories of gradualism and random mutation.