Re: local evolutions

Susan S. Chin (susansf@netcom.com)
Wed, 28 Aug 1996 06:02:36 GMT

Bruce Scott TOK (bds@ipp-garching.mpg.de) wrote:
: On Thu, 22 Aug 1996 09:35:48 -0500, "C. Marc Wagner @ UCS"
: <mwagner@indiana.edu> wrote:

: : I think that this theory has begun to fall out of favor in recent years
: : as genetic evidence has come down on the side of the "Out of Africa"
: : theory that several times in the past Hominids have migrated out of
: : Africa. If I understand it correctly, the genetic evidence suggests
: : that all living Homo sapiens sapiens are descended from a single female
: : who lived around 800KYA. Much later than Homo erectus left Africa.

: I haven't been following this story recently, but when and why did this
: time scale become 800 kya and not 200 kya?

Also, my understanding is that all living humans (H.s.s.) can trace our
mitochondrial DNA to a common female ancestor popularly known as
Mitochondrial Eve (mtEve for short), who lived in Africa about 200,000 yrs
ago. The assumption here would be that this original segment of mtDNA
arose only once and was "housed" in a single individual female, and did not
independently evolve in differing populations and geographic regions.
This is different from "we are all descended from a single female" in
that it's only the mitochondrial DNA which we share with Eve, not
necessarily nuclear DNA, which is much harder to trace due to genetic mixing.

: Yousuf Khan (ykhan@achilles.net) wrote:

: : However, what evidence is there that it did originate in Africa?
: : All we can guess at is how long ago it happened, but that doesn't
: : tell us where it happened: it could've happened in Africa, but
: : not necessarily so.

: According to the original story, the evidence was that there is more
: genetic diversity among humans in Africa than ahywhere else, consistent
: with the hypothesis that diversity expands with time among non-migrating
: populations. Also consistent with this is that the least diversity was
: observed in native people from the Americas.

: : What exactly do you mean? How do you measure genetic diversity?

: I don't remember the details, but it had to do with certain alelle
: frequencies in the mitochondrial DNA. It _was_ however quantitative.
: Look it up in Nature articles from about 1992-1993.

Plus the mtEve Theory has been questioned by other researchers who tried
to duplicate their results using a computer generated program, PAUP
(Phylogenetic Analysis Using Parsimony), and came up with differing, and
more ambiguous results.

For further reading:

"Mitochondrial Eve: Wounded but not dead yet," SCIENCE, August 14, 1992,
v. 257, pp. 873-875.

This is actually a very non-technical account of the mitochondrial Eve
theory. Some of the papers on this topic get a bit too technical for
some of us to fully understand (for me anyway...)

Susan

-- 

                                             susansf@netcom.com