Neanderthals' Cousins, Not the Fockers: the Denisovans


David Reich/Nature
The entire genome of the Denisovans was extracted from a tooth and finger bone.

The film "Little Fockers" is coming out this week, and I look forward to brilliant performances from Robert DiNero, Ben Stiller, Dustin Hoffman and Barbra Streisand to name a few. If you will excuse my cheekiness, I thought of this dysfunctional family when I learned today of the "Denisovans". Let me explain.

The human tree of life appears to have a new branch: cousins of the Neanderthals, the "Denisovans". The New York Times reporter Carl Zimmer has had a busy week. First, he reported on a paper in the Proceedings of the National Academy of the USA of the largest collection of DNA evidence of Neanderthals revealing a social structure that could include cannabilism and sharing of females from different tribes. Now, today, he reports on a paper in Nature that describes a new branch of the human family tree. Prof. Paabo from Germany has once again led a groundbreaking study in the early genetic history of humans!

The cousins' name derives from the Denisova cave in Siberia. According to the abstract from the Nature paper published today (my edits):

Using DNA extracted from a finger bone found in Denisova Cave in southern Siberia, we have sequenced the genome of an archaic hominin. This individual is from a group that shares a common origin with Neanderthals. This population was not involved in the putative gene flow from Neanderthals into Eurasians; however, the data suggest that it contributed 4-6% of its genetic material to the genomes of present-day Melanesians. We designate this hominin population 'Denisovans' and suggest that it may have been widespread in Asia during the Late Pleistocene epoch. A tooth found in Denisova Cave carries a mitochondrial genome highly similar to that of the finger bone. This tooth shares no derived morphological features with Neanderthals or modern humans, further indicating that Denisovans have an evolutionary history distinct from Neanderthals and modern humans.

According to Carl Zimmer's article to be published tomorrow in The New York Times:

Dr. Paabo and his colleagues immediately set about to collect all the DNA in the Denisova finger bone. Once they had sequenced its genome, they sent the data to researchers at Harvard Medical School and the Broad Institute in Cambridge, Mass., to compare with other species.

The Massachusetts scientists concluded that the finger bone belonged to a hominin branch that split from the ancestors of Neanderthals roughly 400,000 years ago. Dr. Paabo and his colleagues have named this lineage the Denisovans.

In the early days of such research, about ten years ago, there was much controversy about the possible contamination of DNA from the scientists' handling the ancient samples, which could confuse data analysis. However, Paabo's group has mastered the art of "clean techniques" to allow the startling results that are coming out at a rapid pace in this decade. At that time, the idea of sequencing an entire genome of more than 3 billion base pairs was a far fetched dream. Now it is common place, even for sampes that are 400,000 years old! Science is grand.

Understanding our past, our social structures, diet, climate and breeding could guide our future, if we are willing to listen. No, it won't prevent dysfunctional families - perhaps that is hard wired in our genome too? Just a thought for the Holidays.

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