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On May 7 th an extra ordinary study was published in Science which reported
an analysis of a portion of the Neandertal genome and suggested that there
was inter breeding between Neandertals and modern humans.

This is very important with implications for our understanding our evolution
and our origins.

Science is making these all available to non-subsribers to the magazine. Let
me know if you have an difficulties finding the articles.

Martin

The article

http://www.sciencemag.org/cgi/content/full/328/5979/680

 I sent yesterday is a good news summary of the recently (May 7, 2010)
publication of the Neandertal genome and the discovery of admixture of
Neandertal genes with modern humans due to interbreeding in what is now the
Near East. However AAAS has created a section of their website The
Neandertal Genome-Background which puts the research into perspective;
http://www.sciencemag.org/special/neandertal/feature/index.html. There are
two sections, I've copied below which are particularly interesting. One has
to do with the question of interbreeding of Neandertals, especially in in
Europe where there is ample fossil evidence of the co-existance for some
time of Neandertals and modern human; the other is about the implications
for theories about the origins of modern humans. modern humans who migrated
out of Africa.

The technical breakthroughs that allowed this study can also be used to
study the genomes of other human fossils especially the recent discovery in
Africa of a suggested branch in human evolution and Flores in the
Philippines which should provide ore information about our origins and
evolution. Stay tuned as it is going to be a wild ride.

There is an podcast
http://www.sciencemag.org/cgi/content/full/328/5979/764-b

about this discovery as well as audio interviews with principles on the
Neandertal Genome Background pages. Neandertals seem to have better cold
adapted than modern humans. However, the preliminary genome results seem not
to show that these genes in modern humans. This is surprising as it would
seem that it would be  of advantage to modern humans living in Europe. Some
of the scientists quoted in the podcast suggest that the earlier data be
reviewed.

Substantial controversy surrounds the question of whether Neandertals
interbred with modern humans. To address this question, Green *et al*.
tested whether Neandertals are more closely related to some present-day
humans than to others.* Because modern humans are believed to have
originated in Africa, if Neandertals diverged from modern humans before
present-day populations began to differentiate, one would expect Neandertal
sequences to match sequences from non-Africans and Africans to the same
extent. Unexpectedly, the researchers found that Neandertals share more
genetic variants with present-day non-Africans than with Africans. These
results can be explained if gene flow occurred from Neandertals into the
ancestors of non-Africans.

The observation that the Neandertal genome appears as closely related to the
genome of a Chinese and a Papua New Guinean individual as to the genome of a
French individual is particularly surprising as there is, to date, no fossil
evidence that Neandertals existed in East Asia or Papua New Guinea. Green *et
al*. thus suggest that gene flow between Neandertals and modern humans
occurred prior to the divergence of European and Asian populations. Based on
comparative genomic data, as well as a mathematical model of gene flow, the
authors further estimate that between 1 and 4% of the genomes of people in
Eurasia may be derived from Neandertals.

*For a description of additional methods used by Green *et al*. to detect
gene flow between Neandertals and modern humans, see the News
story<http://www.sciencemag.org/cgi/content/summary/328/5979/680> by
A. Gibbons.

There are two major competing hypotheses about the origins of modern humans.
The "Out of Africa" hypothesis posits that modern humans evolved from a
small population in Africa and replaced all other hominin populations,
including Neandertals, as they migrated into Europe and Asia. The simplest
form of this model assumes no interbreeding between modern and ancestral
human populations. In contrast, the "Multiregional" hypothesis holds that
modern humans evolved in several regions of the world simultaneously.
According to this view, archaic humans were not replaced by anatomically
modern humans, but rather, gene flow between Africa, Europe, and Asia, led
to the evolution of modern humans from local populations.

The finding that Neandertals are on average closer to individuals in Eurasia
than to individuals in Africa thus presents a challenge to the strictest
version of the "Out of Africa" model; however variations of this model are
plausible. Green *et al*. suggest that mixing of early modern humans
ancestral to present-day non-Africans with Neandertals is likely to have
occurred in the Middle East prior to their expansion into Eurasia. The
authors contend that this scenario is compatible with the archaeological
record, which shows that modern humans appeared in the Middle East before
100,000 years ago while the Neandertals existed in the same region after
this time, perhaps until 50,000 years ago.

Although the Green *et al*. analyses are suggestive of admixture, the role
of Neandertals in the genetic ancestry of humans outside of Africa was
likely relatively minor given that only a few percent of the genomes of
present-day people outside of Africa appear to be derived from Neandertals.
More fossil and genetic data will help researchers further resolve the
relationships between our early ancestors and how they shaped modern human
evolution.


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–––––––––––––––––––––––––––––––––––––––––
Martin Weiss, PhD
Science Interpretation, Consultant
New York Hall of Science

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