Your Ancestors Mated With Chimpanzees

Human Ancestors May Have Interbred With Chimpanzees

To anyone who understands how evolution works, the news that humans and chimpanzees interbred for a considerable period as the two species diverged from a common ancestor will come as no surprise. Evolution is not normally a sudden event or single act of speciation but a long, slow process in which it is impossible to say precisely where one species became two.

From the chimpanzees' point of view, their ancestors mated with humans. I wonder if they would also find the idea fascinating but at the same time slightly disturbing, even a little distasteful.

Scientists comparing human and chimpanzee genomes have found that their X-chromosomes last shared a common ancestor about 5.1 million years ago but all the others appear to have diverged about 6.3 million years ago. In other words the X-chromosome is 1.2 million years younger than the rest of our genome.

It's as though we diverged twice. In fact, this may well be what happened. We began to diverge about 6.3 million years ago, probably into different habitats, but remained similar enough to be able to interbreed when we came into contact for about a million years before finally diverging completely about 5.1 million years ago.

Abstract
The genetic divergence time between two species varies substantially across the genome, conveying important information about the timing and process of speciation. Here we develop a framework for studying this variation and apply it to about 20 million base pairs of aligned sequence from humans, chimpanzees, gorillas and more distantly related primates. Human–chimpanzee genetic divergence varies from less than 84% to more than 147% of the average, a range of more than 4 million years. Our analysis also shows that human–chimpanzee speciation occurred less than 6.3 million years ago and probably more recently, conflicting with some interpretations of ancient fossils. Most strikingly, chromosome X shows an extremely young genetic divergence time, close to the genome minimum along nearly its entire length. These unexpected features would be explained if the human and chimpanzee lineages initially diverged, then later exchanged genes before separating permanently.

Nick Patterson, Daniel J. Richter, Sante Gnerre, Eric S. Lander and David Reich;
Genetic evidence for complex speciation of humans and chimpanzees;
Nature 441, 1103-1108 (29 June 2006) | doi:10.1038/nature04789

I think the most interesting thing [is] this idea that long, extended gene flow seems to have occurred and that this might be a creative mode of evolution.

David Reich, Geneticist,
Harvard Medical School, MA, USA

And this illustrates how speciation is not the creationist parody event. In this infantile parody, evolution is a single event where one entire species changes into a different one through a series of discrete intermediate stages, or more bizarrely one member of one species gives birth to a different species which then goes on to reproduce, presumably with itself, to form a new species.

Apparently creation pseudo-scientists assume their target audience will believe that millions of serious biologists delude themselves into thinking these are realistic scenarios and are either too stupid to see how implausible they are or are simply all conspiring to mislead people for some political or religious reason.

In fact, it's the creationist frauds who are lying for political and/or religious reasons and many of them will have taken the ICR oath that their 'research' and writings will always be in full accord with the biblical account of Creation in Genesis, as a condition of funding and publication. But this tactic plays to the ego needs of an audience of people who want to believe that their ignorance of science gives them a greater understanding of reality than all that studying and research, and who see science as elitist and scientists as all more than a little bonkers.

This is contributing to the idea that species are kind of fuzzy. They become real over time, but it takes millions of years. We probably had a bit of a messy origin.

James Mallet, Geneticist,
University College, London, UK

Speciation is often a very slow process of gradual divergence across a large geographical range as different populations respond to local change or simply drift genetically more quickly than their genes can flow across the entire population. That's not to say it can't be a fairly sudden divergence if one part of a population becomes isolated for some reason, for example the newly-discovered river dolphin, Inia araguaiaensis, which became isolated when geological events led to a population becoming isolated in a branch of the Amazon river system.

Where speciation happens gradually this can lead to the phenomenon of the 'ring species' where the species gradually changes across its range to form a cline but where breeding can occur in some overlapping areas. This appears to have been the situation with evolving humans and chimpanzees for over a million years and it appears to have been the situation with diverging human populations later on where modern humans and archaic forms seem to have interbred and closely related species like Homo sapiens, H. Neanderthalensis and the so-far unnamed 'Denisovans' seem to have interbred so that genes could occasionally flow between species.

1. 'Whatever the Bible says is so; whatever man says may or may not be so,' is the only [position] a Christian can take..."
2. If [scientific] conclusions contradict the Word of God, the conclusions are wrong, no matter how many scientific facts may appear to back them.
3. Christians must disregard [scientific hypotheses or theories] that contradict the Bible.

W.S. Pinkston, J.A. Graham, G. Kuzmic and C. Vogt;
Biology for Christian Schools;
Bob Jones University Press

And of course, in species where sex has a social and recreational role, as well as a reproductive one, this tendency to interbreed would likely have been more marked than where sex depends more on hormones and visual or other sensory stimulation and serves a purely procreational function.

What you will never get a creationist to acknowledge is that this mode of evolution not only would not produce the 'missing link' they keep demanding science produce but that we should not expect to find any. We would expect the fossil evidence to be exactly what it is - a slightly muddled, fuzzy picture with no strong demarcations and a series showing gradual change over millions of years, just as the DNA evidence is reflecting.

This will give scant comfort to those who require evolution to be a childishly simplistic process of sudden change such as one might see in a biology book for the unfortunate children of Christian fundamentalists.

[Footnote] The above discovery was made seven years ago at the time or writing. Love and kisses to the first person who can find any reference to it on a creationist website or in any of their publications.

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