I’m Related to that Guy from Denisova

Archeologists working in the Russian Altai mountains in Siberia recently stumbled across a hominid finger bone while combing through a rock shelter named Denisova Cave. Knowing that this cave proved a fruitful source of Neanderthal and human stone tools in the past, the archeologists’ natural inclination was to assume an association with one of these species. Much to their shock an amazement, the genome mapped from the DNA of the bone belonged to neither humans or Neanderthals, but to an entirely different, previously undiscovered species of hominid.

Based on differences in nucleotide positions in the mitochondrial genome between these various species, it’s clear that this, as yet unnamed, Denisova species was considerably more distant a relation to humans and Neanderthals than they are to one another. Neanderthals and humans differ by 202 nucleotides on average, whereas this new species had 385 positional differences in nucleotides with Homo sapiens and 376 in Homo neanderthalensis. That dates our most recent common ancestor at nearly a million years ago.

Perhaps the most startling revelation from this find is that the specimen from this new species was radiocarbon dated to between 48,000 and 30,000 years before the present. That means that they were nearly contemporaneous with Neanderthals, who disappeared from Asia around 50,000 years ago, and fully so with Homo sapiens. The Denisova Cave has proven so useful a shelter in hominid history, that it becomes easy to imagine the events through which one cousin displaced the other. The timing suggests that this new species from Denisova could have competed indirectly, through access to food or resources, or directly, through interbreeding and conflict, with Neanderthals. Even if more refined dating methods totally rule out cohabitation between the two, the Denisova protoman appears to have occupied the survival niche carved by that predecessor.

What seems more likely is that Homo sapiens occasionally intermingled with these two local hominid species for tens of thousands of years. Any pressure leading to extinction from another hominid likely originated from us. During this period, the same demographic shift between humans and Neanderthals was well underway in Europe. It defies the conventional impression of the wide geographic dispersion and extreme rarity of interaction between various species of the Homo genus.

This conceptual framework is further jilted by the story of Homo floresiensis, whose last skeletal remains date to as recent as 13,000 years ago. Found on the island of Flores, Indonesia, expert speculation suggests this meter-tall hominid may be the origin of the indigenous humans’ mythic Ebu Gogo. Local folklore described the existence of these humanoid creatures in great detail during interactions with Portuguese trading ships as late as the 17th century. Legend continues that the local humans hunted the Ebu Gogo to extermination after they stole food and kidnapped children from human dwellings. While this may easily be written off as coincidental, the likelihood that the relatively small island of Flores was shared by both Homo sapiens and Homo floresiensis contemporaneously is high, and some interaction would almost certainly occur. The jungle conditions are not conducive to fossilization, and so the youngest fossil remains dating at 13,000 years ago does not necessarily preclude the continued existence of the species into modern history.

The full story of these four hominid species and their interactions cannot be completely known. Archaeological findings like the one at Denisova Cave are fascinating, if not oftentimes quizzical and upending, revelations to the complex history of premodern man.

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~ by Wil Finley on March 25, 2010.

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