Re: Change from 48 to 46 chromosomes
Alex Duncan (aduncan@mail.utexas.edu)
15 Oct 1995 01:43:09 GMT
In article <45hi7e$jjl@ednet1.osl.or.gov> donald e. tyler,
dtyler@ednet1.osl.or.gov writes:
>Any evolutionary guesses
>as to how apes with 48
>chromosomes were changed
>to homo sapiens with 46?
All of the large bodied apes have 48 chromosomes. Therefore, someone
would have to come up with some pretty convincing data to demonstrate
that 46 is plesiomorphic # of chromosomes for large hominoids. The last
common ancestor of humans and African apes had 48 chromosomes.
Someone raised the issue of whether or not humans are apes. "Ape" is a
term that has never been well-defined, and is really part of a folk
taxonomy. Until quite recently the terms "ape" and "monkey" were used
interchangably -- in fact they still are used indiscriminantly by the lay
public.
Whether or not humans are apes depends on how you define apes. If apes =
Hominoidea, then humans are apes. If apes are all hominoids except
humans, then obviously...
It's useful to have a term for all hominoids but humans, because humans
are us, and we're so different from the other hominoids. "Apes" is
potentially such a term. However, we then have to recognize that "ape"
is a paraphyletic taxon.
Human chromosome 2 = chimp chromosomes 10 & 11 fused together. I've
forgotten the exact mechanism by which this happens. I think it might be
called a Robertsonian transformation. Different chromosome nos. ARE NOT
necessarily a barrier to interbreeding, BTW. There are species in which
the chromosome no. is variable, with no impact on fertility.
And, in response to someone else's post -- it used to be "common
knowledge" that humans had 48 (44?) chromosomes. I have an old textbook
at home in which that is mentioned. (Piltdown is also treated seriously
-- to give you an idea how old the text is.)
Alex Duncan
Dept. of Anthropology
University of Texas at Austin
Austin, TX 78712-1086
512-471-4206
aduncan@mail.utexas.edu
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