Human evolution and differentiation of races

[Soapy Sam]

This is what the creationists refer to as "microevolution", and proper people refer to as "adaptation". Carried far enough, this might lead to speciation, but it's by no means certain.

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.

 

[Dancing David]

wait...so Homo sapiens could breed with all the other Homos?

like Homo aferensis and Homo neanderthalensis?

cool.

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.

 

[Dancing David]

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.

I think that might be a ring group in recent nomenclature, incapable of breeding usually means more than seperation recently.

 

[RecoveringYuppy]

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.

Homo sapiens idaltu is more certain as a subspecies than neanderthalis.

 

[RecoveringYuppy]

I think that might be a ring group in recent nomenclature, incapable of breeding usually means more than seperation recently.

Do you mean a ring species? A ring species is one where the species occupies a wide range (usually forming a geographic circle) where each sub population can mate with others near it in the circle but not with sub populations on the other side of the circle. There is no clear demaracation of where cross breeding can't occur, just a general fade out with distance. So it is an example of near speciation due to physical separation. What Soapy Sam is describing happens without physical separation, it's a cultural separation (as he said).

 

[WaterBreather]

the entire human race of today is
directly descended from,
the entire human race of 2000 years ago
(at absolute most, most likely far less)

think:

100 years ago = 16 ancestors at least
200 = 256
300 = 4000
400 = 64 000
500 = 1 million

1000 = 1 billion

1500 = 1 trillion

2000 = 1 000 000 000 000 000

there is no such thing as race,
only species

;-j

 

[Madalch]

the entire human race of today is
directly descended from,
the entire human race of 2000 years ago
(at absolute most, most likely far less)

think:

100 years ago = 16 ancestors at least
200 = 256
300 = 4000
400 = 64 000
500 = 1 million

1000 = 1 billion

1500 = 1 trillion

2000 = 1 000 000 000 000 000

100 years back, assumed to be 4 generations, would contain 2^4 ancestors, which is 16. 500 years back would be 20 generations, which would contain 1.05 million ancestors. However, these are not 1.05 separate million people- many of those ancestors, having lived in an era when long distance travel was not the everyday occurrence it is today, would have married second, third or fourth cousins more often than strangers in blood, meaning the same person would account for multiple great*18 grandfathers.

It's probably true that nearly all Europeans are descendants of Charlemagne. It is probably equally true that most Japanese persons are not.

 

[Xephyr]

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

 

[shadron]

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

Your right, Maldach, but with phylogenetic systematics (i.e., the modern clade system of classification) there may be no genus category anymore. The only meaningful category is species, which has the somewhat fuzzy definition that I gave above. In phylogenetics, the two-piece name is still used, but it is assumed to be a two-piece name for the species, and the use of the first part alone as other than as simply an arbitrary species-superior clade is no longer done.

In particular, there is a new series of rules about naming life that is meant to essentially replace the Linneaen system, known as "PhyloCode". The two founders, de Quiroz and Gauthier, have proposed most lately using the same binomial nomenclature but with the understanding above; they explicitly remove the 7-tier classification scheme that Linnaeas proposed, using only clade and species. Of course, like any such striking move in a science it is being heartily attacked by more conservative biologists, mainly those of the Willi Hennig Society. See http://sysbio.oxfordjournals.org/cgi/reprint/48/4/790.pdf, and google "Phylocode".

 

[Delvo]

The fact that race denial, aside from being an obvious, transparent lie, is motivated entirely by political correctness and such and not the slightest bit by science, is demonstrated by the fact that its missionaries even brought it up in this thread at all.

The question was about the rates of change in certain specific traits. That's all. There's nothing else there. The race-obsessed crowd just took something that wasn't about race at all and used it as an excuse to barge in with their racial sanctimony anyway.

This kind of pushy, belligerent preachiness takes a special kind of jackassitude. It's the kind of thing that only religion and politics generate.

 

[shadron]

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 think this is being deprecated on the weight of the DNA sample taken from the Neandertal tooth some time back.

It's doubtful we could breed with all other human species, but is' currently an open question. It appears we didn't breed with out closest known relative neanderthalensis, but it's not known why didn't. Maybe we could have if we tried.

The point is, we didn't. Regardless of the reason, that (in my understanding) makes us separate species.

 

[shadron]

The fact that race denial, aside from being an obvious, transparent lie, is motivated entirely by political correctness and such and not the slightest bit by science, is demonstrated by the fact that its missionaries even brought it up in this thread at all.

The question was about the rates of change in certain specific traits. That's all. There's nothing else there. The race-obsessed crowd just took something that wasn't about race at all and used it as an excuse to barge in with their racial sanctimony anyway.

This kind of pushy, belligerent preachiness takes a special kind of jackassitude. It's the kind of thing that only religion and politics generate.

Well, Delvo, don't be coy. Go ahead and spit it out. What is this "something that wasn't about race at all" that the race denialists excused themselves with while barging in with their racial sanctimony? anyway? I can't find anything in the OP that enlightens me on it. You evidently wanted to get this off your chest, and yet it's not clear what it was, beyond pushy, belligerent, preachy jackassitude, fit only for our two most popular fora besides this one.

Inquiring minds (including Stephen J. Gould) want to know.

 

[Skeptic Ginger]

One thing I can not understand about human evolution, is how races can have differentiated in such a small amount of time.
According to Wikipedia (sorry, can not post the link yet, it is the page "Human evolution"):

The dominant view among scientists concerning the origin of anatomically modern humans is the "Out of Africa" or recent African origin hypothesis,[4][5][6][7] which argues that H. sapiens arose in Africa and migrated out of the continent around 50-100,000 years ago, replacing populations of H. erectus in Asia and H. neanderthalensis in Europe.

This means that all the current differentiation in skin colour, eye colour and so on, between say, an Irish and a Senegalese, has occurred in about 2000~4000 generations (50000~100000years/25 years average per generation).
Can natural selection operate in such a short number of generations?

2,000 reproduction cycles and 50,000 years is a short genetic time frame? I don't see how you come to that conclusion.

Perhaps you are unaware that the human genome has inbuilt variation, or perhaps you are unaware just how much variation exists there.

If you are a microorganism, you can rely on mutation in times of stress to produce genetic variation that will save the species. For more slowly reproducing organisms, the variation needs to be preexisting when the stress occurs.

So some members of the human population are likely already immune to the next mega-pandemic. For bacteria, they can develop a mutation that produces immunity to the next antibiotic after they are exposed.

 

[Skeptic Ginger]

....

To answer your question, the seemingly vast differences between a person from Nigeria and a person from Norway rely on relatively simple genetic [differences]

That too. Regardless of the time frame such differences would take to be expressed which is what Athon was referring to, it doesn't take very many changes to produce large differences. Humans all share the vast majority of our genetic code and very little difference is needed to get different outward appearances.

 

[Skeptic Ginger]

I'd like to echo what Athon said above, and also point out that a great deal of the variation may have already been present: ie. new mutations may not have been necessary (or at least, not very many) to create the apparent differences.

Instead, variation that was already present might simply have been selected on. That is, for instance, certain genes could have been selected out rather than new ones selected in. Get rid of a melanin producing gene, for instance, and you've got whiter skin without needing new variation to arise through mutation. The mutations could have taken place in the past. That's what's great about a large, diverse gene pool and sexual reproduction: you've got access to a great deal of variation for selection to act on when conditions change took quickly for new mutations to arise.

I think it likely that both selection on old variation and new variation arising through mutation likely had a part to play.

But, as Athon said, the differences between the races are really very small, so it's not surprising that it could arise in a short period of time.

Seems my contribution to this thread is redundant.

 

[kedo1981]

From the wikipedia post about raceso take it for what it's worth) "Darwin was himself a monogenist on the question of race, believing that all humans were of the same species and finding race to be a somewhat arbitrary distinction among some groups"

 

[RecoveringYuppy]

The point is, we didn't. Regardless of the reason, that (in my understanding) makes us separate species.

I think there are some exceptions such as if the reason is that they simply never have the opportunity. Two populations of fish don't immediately become separate species if their lake dries up a bit and splits in to two lakes. That will possibly cause them to become separate species but it doesn't happen overnight.

 

[Cuddles]

Put a garden variety Swede next to a native Australian: How much trouble would you really have defining the differences?

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.

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.

It gets even worse if you look at a group like "Latino", which is purely a cultural and lingual grouping and has nothing to do with genetics at all, but is still often referred to as a race.

Of course, some people do take this way too far in a silly PC way to somehow imply that there are no differences between us at all. Obviously that's not true. But what is true is that traditional views of race based almost solely on a couple of visual features, skin colour and facial structure, are at best horribly flawed, and often are just complete nonsense.

When you look at it in a scientific manner, it turns out that while you obviously can group people by how closely related they are, those groups have very little in common with how the term "race" has been used traditionally, and is really of very little use at all. It's not that race doesn't exist at all, it's simply that how people use it is usually very different from how they think they're using it, and that's different again from how it actually should be used.

 

[shadron]

I think there are some exceptions such as if the reason is that they simply never have the opportunity. Two populations of fish don't immediately become separate species if their lake dries up a bit and splits in to two lakes. That will possibly cause them to become separate species but it doesn't happen overnight.

The point is that if they remain apart, even only for a geographic reason, genetic drift will eventually make them separate species, if nothing else does. If they do come back together and interbreed, then they remain the same species if they re-homogenize their genetic material. So your lake of fish will speciate if the rift is maintained; if it isn't, then they won't, because they will merge back together. That would make it hard to tell if speciation is happening or will happen in the future, but in hindsight it becomes a pretty definite yes/no.

EDT: At least theoretically. The practical matter is finding and quantifying the evidence.

 

[RecoveringYuppy]

@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.