Thursday, March 17, 2011

Another Species of Homo??

There is, if you believe the work coming out of Max Planck Institute. According to an article in Der Spiegel:
The human family just got a new relative. Genetic researchers in Leipzig have deciphered the DNA of a hominid species that coexisted with Homo sapiens and Neanderthals around 40,000 years ago. A tiny piece of bone was enough for them to sequence the genome.

The miniscule amount of powder could have sat on a knife point, and yet, according to Johannes Krause, it contains something sensational. The Leipzig-based genetic researcher extracted the fine powder from a minute piece of fossilized bone -- and discovered a whole chapter of mankind's history inside it.
One wonders why the remains of such have not been found. No matter. Onward. This is a follow-up to a story that, somehow, escaped my notice earlier this year, the discovery of the Denisova girl. She, apparently is the representative of a new species of Homo that split off from the main line around 300,000 years ago, and lived in the steppes and Siberia. The speculations are almost lurid:
The scientists posed the question as to how different types of hominids might have interacted with each other. Did they hunt each other? Did they avoid each other? Might they have stolen each other's women? To find the answers to these questions, the Max Planck scientists compared DNA from the Denisova cave with that of modern man. They found no traces of Denisova characteristics in people from Africa, Europe or China. Indeed, clear indications of intermingling were only found among the inhabitants of Papua New Guinea.

The two types of hominids, researchers believe, must have encountered each other somewhere in Southeast Asia. They hypothesize that different Denisova tribes had settled there long before modern man made his way to East Asia some 30,000 years ago. The two groups must have interbred, perhaps not as a matter of course, but periodically. Later, the modern humans and their genetic dowry moved further south, whence today's Melanesians developed.

The Leipzig researchers now want to search Russian and Chinese collections for more fossils that could belong to the Denisova. The hope is to understand what they may have looked like. While the DNA provides hints on several characteristics of the Denisova, appearance is not one of them.
This is not out of the question, since hominids in this time range all belong to that kitchen sink, catch-all grade “archaic Homo sapiens,” which encompasses basically everything that succeeded Homo heidelbergensis up to modern Homo sapiens. It also means that the human family tree is considerably more bushy than we thought at this point in time.

On the other hand, if they found traces of intermingling with Melanesians and other Asian groups, it is not clear how “specific” these individuals were. The original authors have remarked that the Denisova girl represented an out-of-Africa migration, a conclusion that has been challenged by Martinón-Torres et al. 1 These authors write:
The evidence that the ancestors of Neanderthals (i.e., H. heidelbergensis) left Africa ca. 500–300 ka is currently inconclusive, and the origin of H. heidelbergensis remains enigmatic. Whilst dispersals out of Africa might have occurred ca. 1.0 Ma, large-scale dispersals within Asia were also probable, and thus an Asian origin of the Denisovans cannot be excluded. These issues cannot be resolved without substantial improvements in the dating of key specimens, without an enlarged Asian fossil hominin record (particularly from SW Asia), and without a much more detailed Middle Pleistocene climatic record from SW Asia and NE Africa. Although the Denisova evidence is undoubtedly a fascinating piece in the jigsaw puzzle of human origins, it would be premature at present to determine the part of the picture to which it belongs.
Given what we know about Neandertal DNA showing up in the modern human genome, the remains from Denisova may yet suggest a very wide-range polytypism in the human record during the transition from archaic to modern Homo sapiens.

1Martinón-Torres, M., Dennell, R., & Bermúdez de Castro, J. M. (2011). The Denisova hominin need not be an out of Africa story. Journal of human evolution, 60(2), 251-255.

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1 comment:

  1. Can't stay, I'll be back to read more articles. I found you doing research on Denisova, and I have to keep going.

    I wanted to tell you, though, that this looks like a blog I need to stay in touch with. I added you to my Google Reader. It's hard to find quality sites about science by Christians.

    Quick note to you. Have you seen John Hawks blog? I found it the same way I found yours, just tonight, and it seems like you'd be interested in it. He's working in the Denisova cave, and he's a blogger!!!