OK, I don't have oodles of time today to get embroiled in this
controversy, but some people have written to me and pointed out that
there are some anthropologists who dispute the claim about the
recently published (in this week's Nature) discovery of an unknown
hominin from the mitochondrial DNA of a finger bone found in a cave in
Siberia. Many of these anthropologists are getting upset about the
claim that these people have discovered a new "species."
Much to the horror of some people on this listserve, I am going to
attach a very small figure to this e-mail message that is from the
original article.
Now that you have recovered from the shock of receiving an attachment,
let us peruse the above results and make some observations as well as
ask some questions (the "Denisova-human" is the DNA from the
aforementioned finger bone).
1) It would seem that the difference in mitochondrial DNA sequence
between Neanderthals (Homo neanderthalensis) and modern humans (Homo
sapiens) is considerably less than the difference between the DNA of
the Denisova-human and the Neanderthal-human.
2) There is an even larger difference in mitochondrial DNA between
modern humans and the Denisova-human.
3) Why is there a bimodal distribution for modern human mitochondrial
DNA? (don't ask me the answer to this question, but if you know the
answer I'd love to hear it--though I expect the answer is just "that's
what is observed").
4) Did Neanderthals and Pleistocene humans ever mate and produce
fertile offspring? There is some nuclear DNA evidence that they might
have done so, and that Homo neanderthalensis is a subspecies of Homo
sapiens--but this remains controversial.
5) Did the Denisova-humans mate with Neanderthals and/or Pleistocene
humans and produce fertile offspring? Not enough evidence is available
at this time to answer this question.
6) What does it mean to be a different species?
The last question is akin to asking the question, "how long is a piece
of string"? Traditional anthropologists will answer the question one
way and require more fossil evidence. Animal husbandry experts will
cite the fact that mating a horse and a donkey produces the infertile
mule offspring, thereby establishing that horses and donkeys are
different species. Modern-day microbiologists will tell you that our
concept of a species is in flux, primarily due to their analysis of
the burgeoning amount of DNA sequence data for bacteria. The fact is
that the authors of the paper never once claim that they have
discovered a new species, but instead claim that this is an "unknown
hominin." (The title of the paper is "The complete mitochondrial DNA
genome of an unknown hominin from southern Siberia.") And yes, the
author of the Nature News article (a professional journalist) uses the
term, "new species" when describing the results of the paper. Relax a
bit and realize that (as my father used to always say), you can't
always believe what you read in the newspaper, because journalists
aren't experts in any field except reporting other people's results,
and often they do it badly.
Once again, if you'd like to read the original paper, I can send it to
you as a PDF.
Diana
* * * * * * * * * * * * * * * * * * * * * * * * * * * *
Diana R. Tomchick
Associate Professor
University of Texas Southwestern Medical Center
Department of Biochemistry
5323 Harry Hines Blvd.
Rm. ND10.214B
Dallas, TX 75390-8816, U.S.A.
Email: [email protected]
214-645-6383 (phone)
214-645-6353 (fax)
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