Leaky Replacement Model
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12-05-2014, 07:18 AM (This post was last modified: 12-05-2014 07:28 AM by ghostexorcist.)
Leaky Replacement Model
The prevailing hypothesis for human origins is the Out of Africa (OOA) hypothesis in which we are believed to have originated in Africa and then spread out to colonize the world. The strictest version of this hypothesis is that modern humans replaced archaic species with little to no interbreeding. This is obviously common knowledge to those who have studied human evolution to some extent. One of the things that I was surprised to learn in my Fossil Evidence for Human Evolution class is that there are a small minority of scientists who still fervently argue in favor of the Mutli-Regional hypothesis in which all of the various human populations are believed to be descended from Homo erectus or one of its immediate descendants. For instance, the people of East and Southeast Asia are believed to be descended from H. erectus, while the people of Europe are descended from H. neanderthalensis. Another version of this hypothesis is that modern humans are the result of the interbreeding between archaic groups descended from H. erectus. A mountain of fossil and genetic evidence continues to pile up against this minority group, but they continue to interpret the new findings in a way that they feel supports their stance. They are sort of like the creationists of the scientific community.

(One of the reasons I don't like the Multi-Regional hypothesis is that racist groups try to use it to show that populations supposedly evolved from archaic groups are somehow inferior. For instance, an individual on a history forum I frequent tried to argue that Australian aboriginals are inferior to whites because they are evolved from H. erectus. The biggest problem with this is that the supposed continuity between the two groups is simply a conflation of shared archaic traits. Fossil evidence shows that aboriginals arrived in Australia long after H. erectus died out. Since they were one of the first modern human groups to colonized Australia, they still contain some robusticity known to early h. sapiens. These same robust features appeared in other populations in different parts of the world, according to fossil evidence. It's just that the features of these populations happened to gracilize overtime.)

Well, an old hypothesis known as the Leaky Replacement model, which is a mix of the two aforementioned hypotheses, is starting to gain traction in academia. Make no mistake, this hypothesis still strongly supports the OOA hypothesis, but accepts more instances of interbreeding between different modern and archaic groups than originally acknowledged. This increased emphasis on interbreeding is the result of genetics testing that shows admixture between modern humans, Neanderthals, and Denisovans. The main idea of the hypothesis is that after we left Africa humans interbred and coexisted with archaic groups instead of outright replacing them like the strictest form of OOA posited at one time.

You can read more about the hypothesis in this brief paper.

http://genetics.med.harvard.edu/reich/Re...w_View.pdf

Here is a diagram comparing the three hypotheses.

[Image: t5z4.png]
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12-05-2014, 02:50 PM
RE: Leaky Replacement Model
I have heard of this model. Always interest me on human migration from Africa. Though if the other is true how are we all homo sapiens?

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12-05-2014, 03:17 PM
RE: Leaky Replacement Model
(12-05-2014 07:18 AM)ghostexorcist Wrote:  This increased emphasis on interbreeding is the result of genetics testing that shows admixture between modern humans, Neanderthals, and Denisovans. The main idea of the hypothesis is that after we left Africa humans interbred and coexisted with archaic groups instead of outright replacing them like the strictest form of OOA posited at one time.

Thanks for the link.
From what little I've read previously, I kind of find this hypothesis more reasonable - it seems to account for a lot of overlap.

Denisovans; who knew? Shy

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