Human evolution and differentiation of races

[godless dave]

No- breeding is possible between members of the same species, not genus.

...usually.

 

[lomiller]

I am only lightly read on this subject, but from what I recall with the explosion of genetic studies genetic biologists were surprised at how little variation humans actually have. Something less than single breeds of some cats and dogs. The various adaptive variations in humans are very minor differences. Even within a handful of generations we can witness changes in skin tone, height, build ect among a small group.

It is not uncommon for people to think skin color variation is a major trait differnce, but it is incorrect.

This.

Humans have one of the least varied genomes of any large mammal. It’s suspected there were as few as 1000-2000 breading pairs as recently as 60 000 years ago. One hypothesis attributes this to a rapid cooling event caused by the Mt Toba eruption 65000 years ago.

im no biologist, but I do know that the eye color, hair color, hair texture, and skin color, make up a miniscule amount of our genetic blue-print. let alone the fact that humans, no matter where they come from, can all interbreed.

I’ll try and find it but I saw a paper recently that suggests the genes that control skin and hair pigment in humans are identical to the ones that control it in chimps.

we are all one species..and our racial differences are purely skin deep.

Humans are not just one species, but one sub-species.

 

[Skwinty]

Humans are not just one species, but one sub-species.

Yes, we are all members of the human race, big and small, black red or white.

 

[ddt]

Humans have one of the least varied genomes of any large mammal. It’s suspected there were as few as 1000-2000 breading pairs as recently as 60 000 years ago. One hypothesis attributes this to a rapid cooling event caused by the Mt Toba eruption 65000 years ago.

This post at MadSci offers another intriguing possible explanation for the lack of genetic variation within humans. Human chromosome 2 results from translocation of two primate chromosomes. This may have posed a barrier to interbreeding and given the first hominids a very small genetic base to begin with.

 

[lomiller]

But this is exactly the point - people think they can easily see the difference, but it turns out that when you look at the actual genetics, what people think often turns out to be wrong. For example, take two African Americans (often considered by many people to be a race) and a random white American. It's not particularly unlikely that each of the black people will be genetically more closely related to the white one than they are to each other. So how could African American possibly be a race? The answer is that it isn't - basing the idea of race purely on looks just doesn't work.

Not that I disagree, but it may have been better if you stated it the other way. There is more genetic variation within Africa then outside. This means that if you take a random “black” person who descends from west African ancestors and one who descends from east African ancestors there is a better then even chance they will be less closely related then a person who descends form Asian ancestors and a person who descends from European ancestors.

The fact that genetic groupings exist is basically irrelevant. In fact so many potential groupings exist that you go looking are bound to find something that fits any group you wish to identify. Since you can essentially drop people into such groups at will, the groupings themselves are basically irrelevant.

A much more useful way to use infra-subspecifc classifications (groups below the level of sub-species) is to define them ad-hoc based on what you wish to look at. For example the ability for adults to digest fresh milk appears to have arisen in central Europe ~7500 years ago and radiated outwards. (this is one specific change, there may be others that give the same result). This, IMO, would be a grouping worth looking at and far more relevant then some static grouping whose sole purpose is to line up with outdated “racial” groupings.

 

[Wowbagger]

Did no one mention "run away" sexual selection, yet?! That could also be a cause for "races" to diverge rapidly.

Though, I argue that there is, ultimately, really no such thing as "race", the term could still be of valid taxonomic usage, when studying proximate causes of human social behavior.


ETA: "Race" could also be of use to immunology. Some "races" could be statistically more prone to be immune to certain things than others.

 

[shadron]

@shadron,

Yes, but in regards to Neanderthal we can't tell whether they'd split long enough or early enough to diverge in to a separate species incapable of renewed interbreeding. Evidence is still a bit short for a conclusion.

From what I've gathered and learned, it doesn't make any difference in a taxonomic view whether they could interbreed; only that they didn't, as demonstrated by the genome analysis, which is the best kind of evidence we can have at this point in time.

 

[Skeptic Ginger]

Carried far enough, simple cultural differences can lead to speciation.

If Catholics never married protestants, you would have (effectively) 2 species of human. The fact they could interbreed if they chose to is irrelevant, so long as they don't.
All of which illustrates the fact that "species" is a human taxonomic concept and nothing more.

While taxonomic divisions are often on a continuum rather than every species being divided by punctuated equilibrium, you need isolation and lots of generations before you get a species division.

Take the Australian Aboriginal, for example. They were isolated for 40-60,000 years or so until a couple hundred years ago. Yet intermarriage has occurred since the continent was populated with other humans a couple hundred years ago. You cannot say that 40,000 years of isolation led to speciation. Clearly it did not.

 

[Skeptic Ginger]

The nomenclature is not clear in the taxonomy of homo, we are technicaly homosapiens sapiens the other member of the species is homo sapiens neanderthalis but that s all conjecture.

I'm not sure what conjecture you are referring to here? It's my understanding DNA has been recovered from Neanderthal bones and they appear to be a side branch rather than an ancestor or interbreeder with h. sapiens. Doesn't that settle the question?

 

[Skeptic Ginger]

Correct me if I'm wrong, but from what I understand, environmental adaptation does normally occur rather quickly in most species.

"Quickly" is a relative term dependent in this case on reproduction rates.

Perhaps the right something that wipes out 95% of a population can effect change quickly as the seed group is instantly narrowed.

 

[Soapy Sam]

While taxonomic divisions are often on a continuum rather than every species being divided by punctuated equilibrium, you need isolation and lots of generations before you get a species division.

No you don't.
You just need two groups that don't interbreed. Whether they can or not is irrelevant.
We have no research to show that (for instance) a tawny pipit and a red throated pipit can't interbreed. We know they don't and that's why they are defined as belonging to two different species.
The example of ring species has been given-Lesser Black- Backed and Herring gulls are seen as two species, because they don't interbreed, though it turns out they do , through various hybrids with restricted geographical ranges. Take out the intermediates and you have two new species overnight- but they might be perfectly viable if they ever mated. They just don't.

The point is that "species" is a human label. We should use it as a tool, not a straitjacket. Darwinism would be much easier to explain to woo-woos if they weren't so god-damnedly insistent on the inviolability of species.

 

[Soapy Sam]

"Quickly" is a relative term dependent in this case on reproduction rates.

Perhaps the right something that wipes out 95% of a population can effect change quickly as the seed group is instantly narrowed.

There's the much debated Toba "bottleneck" around the right sort of time.
Not convinced myself, but the evidence seems to be growing.

 

[shadron]

No you don't.
You just need two groups that don't interbreed. Whether they can or not is irrelevant.
We have no research to show that (for instance) a tawny pipit and a red throated pipit can't interbreed. We know they don't and that's why they are defined as belonging to two different species.
The example of ring species has been given-Lesser Black- Backed and Herring gulls are seen as two species, because they don't interbreed, though it turns out they do , through various hybrids with restricted geographical ranges. Take out the intermediates and you have two new species overnight- but they might be perfectly viable if they ever mated. They just don't.

The point is that "species" is a human label. We should use it as a tool, not a straitjacket. Darwinism would be much easier to explain to woo-woos if they weren't so god-damnedly insistent on the inviolability of species.

A definition / explanation after my own heart. I emphasize what Soapy says about the label of species being a tool, which is inconsistently applied by not only laymen and Christians, but biologists as well. However, it is the only part of Linneaus's 7 part category system that has an operational rather than just an relative definition.

 

[Skeptic Ginger]

No you don't.
You just need two groups that don't interbreed. Whether they can or not is irrelevant.
We have no research to show that (for instance) a tawny pipit and a red throated pipit can't interbreed. We know they don't and that's why they are defined as belonging to two different species.
The example of ring species has been given-Lesser Black- Backed and Herring gulls are seen as two species, because they don't interbreed, though it turns out they do , through various hybrids with restricted geographical ranges. Take out the intermediates and you have two new species overnight- but they might be perfectly viable if they ever mated. They just don't.

The point is that "species" is a human label. We should use it as a tool, not a straitjacket. Darwinism would be much easier to explain to woo-woos if they weren't so god-damnedly insistent on the inviolability of species.

I don't recall defining "isolation" as requiring physical barriers.

Human mate choice is much more complex than the bird examples you've cited. If you had evidence that social rules absolutely resulted in population isolation, you could make your case. The closest we have of voluntary isolation is probably something like the Azkanazi Jews. And even in that extreme members did not keep to perfect interbreeding.

In the absence of any evidence supporting your hypothesis as being a valid means of isolating human groups, all you have is a hypothetical.

 

[Skeptic Ginger]

A definition / explanation after my own heart. I emphasize what Soapy says about the label of species being a tool, which is inconsistently applied by not only laymen and Christians, but biologists as well. However, it is the only part of Linneaus's 7 part category system that has an operational rather than just an relative definition.

Imperfect or not, inappropriately applied or not, you can say with certainly there are species.

Just because some species have gray divisions doesn't diminish the concept of speciation and subspeciation.

Astronomers have the same problem defining planets. I liked DegrassTyson's view that the divisions make the most sense if they tell you something about the object. So drawing a line of mass and calling A a planet and B an asteroid is not nearly as useful as dividing planets by how they formed, by what part of the solar system they are and so on. Pluto is a Kuiper Belt Object. It isn't its size that makes it not a planet.

In biology, it seems to me the taxonomies should reflect similar rules. Interbreeding is one such 'rule' that results in a continuum division actually telling us more information than simply how many genetic mutations divide two organisms. I suspect there are other kinds of information which species definitions could tell us if we chose our dividing lines with that goal in mind.

 

[UnrepentantSinner]

Or another example. Take your native Australian and put him next to a native South American. They may well look very similar. But the South American is probably much more closely related to an extremely white Russian who you'd probably group with the Swede, since that's where the main migrations that colonised America originated. Once again, the concept of race based on looks falls apart.

While I concur with the general idea you're advocating, I'm not sure about some of the specifics.

 

[Soapy Sam]

I don't recall defining "isolation" as requiring physical barriers.

I' m sure you didn't.

Human mate choice is much more complex than the bird examples you've cited. If you had evidence that social rules absolutely resulted in population isolation, you could make your case. The closest we have of voluntary isolation is probably something like the Azkanazi Jews. And even in that extreme members did not keep to perfect interbreeding.

Oh aye, love will find a way. Bird mate choice might be more complicated than we think too. We just know more about humans. The point is that it seems 40,000 years of geographical isolation has not rendered the opposite ends of the Great African Diaspora unable to interbreed, so it might take social isolation at least as long to achieve that result and few human institutions are apt to last that long. But in principle, any isolation will do.

If we are to define species as an actually viable interbreeding group, then you and I would seem to be different species! In order to prove we are both human, we would need to get together and see what happens. But if we accept the definition of potentially viable breeding group, then we almost certainly need to throw away a vast number of existing species as mere variants.

In the absence of any evidence supporting your hypothesis as being a valid means of isolating human groups, all you have is a hypothetical.

Exactly- but that's my point. "Species" are hypothetical constructs.

 

[Dancing David]

I'm not sure what conjecture you are referring to here? It's my understanding DNA has been recovered from Neanderthal bones and they appear to be a side branch rather than an ancestor or interbreeder with h. sapiens. Doesn't that settle the question?

That naming may not match reality.

 

[epix]

how long would human groups have to be separated to become separate species?

There is not enough knowledge and computing power to run a model -- the former being the greater obstacle -- but you could possibly consider the separation of the Neanderthals and the early Homo sapiens. The Neanderthals may not have left Africa as the same species they were when they disappeared.

 

[The Fallen Serpent]

Speciation occurs with a variety of factors, so time even when measured in generations is not an easily predicted factor. Two isolated groups may be subject to similar enough forces that natural selection may not produce genetically incompatible populations even over great spans of time. Another pair of isolated groups may be subject to vastly different conditions, selecting towards different genetic variations and leading to genetic incompatibility in a relatively short span of time.

Tens of thousands of years does not appear to be enough with the extremes of environment that humans can survive in.

Soapy Sam, with your point about potentially viable breeding groups defining species I understood this was a driving focus in current classifications based on genetics and ancestry. Wolves, dogs, dingoes and such are all variants of one species. Domesticated cats, wildcats and so on being another. Hence the erosion of the concept of genus.

I suppose having multiple definitions of species is useful as long as the appropriate definition is used in the context presented.