Science a GoGo's Home Page Forums General Discussion General Science Discussion Forum genetic gradients - humans also?

Now this is faily old (Jan 2005) and may have been brought up at the time:

http://www.scienceagogo.com/news/20050020225317data_trunc_sys.shtml

I've posted elsewhere some diagrams of human genetic gradients in Europe (I forget where but I'll look for it). It's obvious there are genetic gradients in the human population today. I maintain that this has always been so, even in Homo erectus times. Regional continuity theory says evolution proceeds by gene flow. We have been one continually evolving species since Homo erectus times. Any disagreement?

Quite a quote from that link.
"With massive habitat destruction being caused by humans, these gradients are being destroyed, as are the stories they tell about evolution and biodiversity. This is happening in much of Asia, where there is a tremendous loss of habitat from humans. Ten years from now, I'm not sure I would be able to find this same evidence."

So Terry, re: "We have been one continually evolving species since Homo erectus times."

Are you asking if we've never "interbred" with recent sidebranchs?
...such as Neanders; or further back like w/ Java, Peking; or further back (2Myr.) with contemporaries in the Rift area/elsewhwere (like if chimps and bonobo's mated)?

~~SA

Or are you building evidence againsy the 'Out of Africa' theory. There was a discussion earlier in this forum about Neanderthal DNA and whether there had been interbreeding with modern humans, with a fairly non-conclusive resolution I thought.

I have trouble accepting that modern humans totally replaced other humans around at the time. The following should probably go on chapter VII on the Darwin thread. I believe the "out of Africa" theory gains support from the wish to stress the complete separation of modern humans from other animals and even earlier humans. Darwin's contemporaries had trouble understanding how advantageous characteristics could expand through a population. They had no knowledge of DNA, let alone genes. So when the economic term "survival of the fittest" was coined in economics it was seen as an explanation for the problem and rapidly taken up. Obviously many people are still stranded in victorian ideas of how evolution works as TheFallibleFiend and I are trying to explain elsewhere.

It is inconceivable that the various regional varieties of ancient humans didn't form hybrids as they moved around, exactly the same way as the greenish warblers in Asia mentioned in the link. The authors exagerate when they say "that few examples of such species are known today". Great tits, herring gulls and various species of deer are other examples that I immediately think of.

Samwik. Chimps and bonobos are hardly separate species. They readily form fertile hybrids. The ancestors of chimps and humans formed hybrids for more than three million years before they finally separated.

So 'no,' you weren't asking about that, I guess. I agree that probably there were hybridizations along the way. I just learned of bonobos recently (& don't know much) and didn't think they were separate species, but they seem like a unique population. Maybe not a "recent side branch," but more like a side bud (or potential bud)?

So are you asking if we agree with 'evolving from H.erectus,' as opposed to a de novo genesis 6000 years ago (with the misleading gradient in place)?

~SA

Basically yes. But the genesis seems to be placed slightly more than 6000 years ago although the motivation is the same. Dates anywhere between 40,000 to 200,00 years are proposed for a sudden evolution of modern humans. We know that species form genetic gradients through both time and space and when we compare opposite ends of either extreme we see the greatest difference. There is usually no really sudden huge leap in either gradient although geographic features and elements of punctuated equilibrium lead to reasonably abrupt changes. Make sense?

Regarding bonobo/ chimp separation, about 2 million years I think is generally accepted. Couldn't find anything definite with a quick search.

I think I get it now. It's the difference between gradual change (although variable in speed) and abrupt change (like an alligator laying a chicken egg). Is that the question?

~~SA

That's pretty much it Sam. I don't know if you're familiar with the geologist James Hutton (died 1797). He came up with the comment, "We can see no vestige of a beginning, no prospect of an end". The problem is we like to have a defined beginning. Unfortunately there is rarely such a beast.

I disagree. "Out of Africa" gains no support from any wishful thinking on the part of people who already accept evolution as the best theory we have for species diversity. Keep in mind that it was first assumed that Neandertals and many other pre-human primates were in our direct lineage. Also keep in mind that researchers in mtDNA studies of Neandertals and humans start with the assumption that there was interspecies sex.

Personally, I'd believe or disbelieve that Neandertals are in our relatively recent lineage based on hard evidence. So far, the evidence leans toward no interbreeding with Neandertals.



When you're talking about small populations seperated for long periods of time, there might not be a lot of opportunity for interbreeding. Also, the fact that you can produce fertile, interspecies crosses in zoo or lab environments does not mean these crosses will happen in the wilds. Bonobos are different species than chimps. They behave quite differently, which probably is the reason you don't see hybrid populations or mixed populations between bonobo and chimp habitats.

Sorry to burst into the middle of a conversation. You may have already gone over this stuff. If so... sorry.

I'm inclined to agree with soilguy here, but overall I think there are even other possibilities that we aren't aware of yet.

When I asked, "It's the difference between gradual change (although variable in speed) and abrupt change (like an alligator laying a chicken egg). Is that the question," I had decided to hold back on one additional comment for later.

So here I'll now add, I think both mechanisms are possible and work (at different times and in different amounts). But I also think "there are even other possibilities that we aren't aware of yet." And this applies both at the molecular level and the environmental level.

More later,
Thanks,
~~SAMwik

I'll explain a bit more.

In captivity pygmy chimps form fertile hybrids with other chimps. The reason they are unable to do so in the wild is the same reason eastern and western chimps don't form hybrids. Their geographic ranges don't overlap. Surely by any definition of species they are therefore simply regional varieties or subspecies. A couple of links:

http://www.sciencedaily.com/releases/2007/04/070420104723.htm

http://images.google.co.nz/imgres?imgurl=http://www.solcomhouse.com/afbig.gif&imgrefurl=http://www.solcomhouse.com/greatapes.htm&h=440&w=440&sz=17&hl=en&start=9&um=1&tbnid=yxgyh8a54xLfNM:&tbnh=127&tbnw=127&prev=/images%3Fq%3Dmap%2Bdistribution%2Bchimpanzee%26svnum%3D10%26um%3D1%26hl%3Den%26sa%3DG

If, at some time in the past, bonobos had shared a range with other chimp species one of three thing would have happened. Most likely they would have formed a stabilised hybrid, a subspecies with characteristics of both original subspecies. The next most likely result would have been extinction of one subspecies. The third possibility is that they would have developed isolationg mechanisms and split the environment ecologically. I can't think of any others.


Our own eyes tell us there are genetic gradients or clines in the modern human population just like the greenish warblers. No-one would have trouble distinguishing modern humans originating in Asia from those originating in Europe. But we have two problems. Firstly identifying the genes that have given rise to the regional differences and secondly identifying how far back in our evolution these mutations occurred. Neither problem is anywhere near solved. Way back there was a thread that mentioned some human genes with a regional distribution had an origin much earlier than 50,000 years ago. The work has been criticised but if true these genes can only have entered the modern human gene pool from populations present in those regions before the modern human expansion.

Like all species spread over a large geographic range Homo erectus developed into subspecies, especially at the extremities: Southeast Asia, China, Europe and Africa. It has become accepted one of these regional varieties expanded from its original home and exterminated all other subspecies. No wonder genocide is so widespread. It has a long and noble history in our species.