Tuesday, November 14, 2006

Living Neanderthals

The science blogosphere has been abuzz about the recent papers showing evidence of interbreeding between humans and neanderthals. First, Lahn and colleagues reported in Science that one human variant of microcephalin, thought to be involved in regulating brain growth, appeared to have evolved more than a million years ago, but only appeared in the human population 37,000 years ago (Evans et al. "Evidence that the adaptive allele of the brain size gene microcephalin introgressed into Homo sapiens from an archaic Homo lineage" Proc Natl Acad Sci (2006)).
The Lahn group concluded that the most likely scenario was interbreeding between prehistoric modern humans and a now extinct hominid that carried haplogroup D--most likely Neandertals. The haplogroup was probably beneficial enough to spread quickly in modern human populations, says Lahn. But he's not sure what advantage it offered. Because most researchers agree that Neandertals were not as cognitively advanced as modern humans, Lahn and his coauthors suggest that the haplogroup might have made Homo sapiens better able to adapt to the Eurasian environments that Neandertals had occupied long before modern newcomers arrived. (ScienceNOW article)
John Hawks has a nifty FAQ about the science. His colleague, Greg Cochran, speculates that Neanderthals may have given the human race a boost:
So when you think about the cultural explosion that occurred shortly after we overwhelmed the Neanderthals (cave paintings, sculptures, new tools and weapons, all that jazz) - well, you have to wonder if assimilating a passel of adaptive alleles in a few thousand years, way more than the typical number that would arise and become established over such a short time span, didn't give us a hell of a boost. There are signs of behavioral modernity a bit earlier in Africa - but those ostrich eggshells are dull as hell compared to Gravettian cave paintings. Expansion out of Africa must itself be a sign of new capabilities (I'd bet on sophisticated language) but you only see full-fledged behavioral modernity in the European Upper Paleolithic... Judging from neutral genes, it can't have happened often, but those few furtive human-Neanderthal couplings may well played a crucial role in the future development of the human race. I'm sure that this notion will suggest new pick-up lines to some readers.
Gene Expression rounds up the blogs discussing the results.

I have to confess, that when I read about interbreeding humans and Neanderthals, the first book that came to mind was Jean Auel's Clan of the Cave Bear. That doesn't really fall into the "science fiction" category, though, so I'll move on.

Neanderthals have made a number of appearances in the science fiction literature, most recently in Robert J. Sawyer's Neanderthal Parallax trilogy: Hominids (winner of the 2003 Hugo for best novel), Humans, and Hybrids. The novels are set on our earth and a parallel earth where Neanderthals became the dominant hominid. If you want more information about his take on Neanderthals, read Sawyer's essays Commiting Trilogy: The Origins of the Neanderthal Parallax and Neanderthals are a Separate Species, and his invented system of Neanderthal timekeeping.

There have also been numerous other science fiction stories with Neanderthal themes, such as:
• Greg Bear had a different take on the relationship between Neanderthals and humans in Darwin's Radio. One of his heroes, scientist Mitch Rafelson, find the frozen remains of a Neanderthal couple and their apparently human infant.
• In Paul Levinson's novel The Silk Code (winner of the 1999 Locus Award for best novel), forensic scientist Phil D'Amato investigates the possibility that a small group of Neanderthals have survived to the present day.
• Short story "Scout's Honor by Terry Bisson (read free online), stars scientist goes back in time to study Neanderthals
• Talk.origins also has a list of Paleoanthropology Fiction.

I'm sure there are others*.

It seems likely that we carry a little bit of the Neanderthal in us. I suspect that the sequencing of the Neanderthal genome will turn up even more "survivors".

* For example, there is a short story in which modern cloning and genetic techniques are used to bring Neanderthals back to life. They subsequently take over the world. Unfortunately, I can't remember the title or the author.

ETA 11/16: I should have waited a few days to post. Nature just published an article from the Pääbo lab analyzing 1 million bases of Neanderthal DNA (Green et al. "Analysis of one million base pairs of Neanderthal DNA" Nature 444:330-336 (2006)). Nature has collected text, video and audio links on the subject. An additional 65,000 bases were published in this week's Science (Noonan et al. Sequencing and Analysis of Neanderthal Genomic DNA Science 314:1113-1118 (2006)). ScienceNOW sums it up:
As expected, the Neandertal and human genomes proved more than 99.5% identical. Rubin's team calculated that the most recent common ancestor of the two human species lived about 700,000 years ago, whereas Green's analysis of 1 million bases found a more recent divergence time, about 465,000 to 569,000 years ago. As to the question of interbreeding, Rubin's group found no sign of it, but Pääbo's group did. "Taken at face value, our data can be explained by gene flow from modern humans into Neandertals," most likely from modern humans fathering children with Neandertal females, says Pääbo.
Afarensis and Gene Expression have more on models of human evolution.

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3 comments:

meika said...

Neandertals have an occiputal ridge (a bump on the rear of their skulls) see the image at
http://www.physorg.com/news82311440.html

Now I have an occiputal ridge too, neither of my parent's have it, so the question is,

Am I a Neandertal freak?

Or is it just all the red heads.

Peggy said...

I would consider it "classic" rather than "freakish" :-)

Anonymous said...

Hi, nice post. At the end, we hear about Neanderthal men fathering hybrid children with modern mothers, and I'm not sure if this merely reflects the (mistaken,imo) belief/paradigm that states the only way that moderns would mate with Neanderthals only under duress or coercion - reinforcing a stereotype of savage beasts of Neanderthal men abducting innocent moderns - while at the same time no self-respecting modern man would consort with a Neanderthal woman. Bearing in mind that the two species lived cheek by jowl in Europe for up to 15,000 years (40, - 25,000 years b.p.), the gene flow over that era could have followed extremely complex patterns, rather than the one-way traffic model suggested by Paabo et al.

I also wanted to say thanks for posting all the book and story links on palaeo-fiction, loads of stuff I've never even heard of, cheers, Tim