Much of this posting would have been unnecessary had Jones read and
understood the postings of the past few days. As it is, however, he
misunderstands 1) the likelihood of the out-of-Eurasia hypothesis; 2)
the time scale of human divergence; and 3) hominoid relationships and
1. relative likelihoods of out-of-Africa and out-of-Eurasia
hypotheses for explaining *mtDNA* origins.
In article <1991Nov19.224202.7072 at cco.caltech.edu>,morphy at cco.caltech.edu
(Jones) quotes Larry Moran and responds:
>>This is an interesting point but I don't see why it is relevant. Let's assume
>>that Homo sapiens sapiens arose in Eurasia . . .
>>This is simply far less likely than the scenario suggested by the data. Why
>must we bend over backwards to avoid the conclusion that afrogenesis is the
>most likely hypothesis?
Keith Robison made a statement similar to that of Jones (without the
"why must we bend over" insulting part) earlier this week, and Jones
should read the objections to that statement before making it
again. The out-of-Eurasia scenario is not "far less likely" when one
uses parsimony to calculate the minimum number of migrations given the
mtDNA tree of Vigilant, et al (1991). Rather than being "far less
likely", the out-of-Eurasia scenario is only *slightly* less likely.
This difference in the likelihood of the two scenarios loses its force
when one considers that a) the tree and its rooting have undetermined
statistical likelihoods, and b) the applicability of the parsimony
method can be questioned on theoretical and empirical grounds. A
separate issue that I will address in a future posting is that the
question of *mtDNA* origin is not the same as the question of gene-pool
origin, nor is it the same as the question of species origin.
2. Confusion about time frame involved.
Jones continues, quoting Larry and then responding:
>>Keith, can you construct an Out-of-Africa senario that is so obvioulsy more
>>reasonable and more simple? . . . an early population
>>would have had to migrate out of Africa but some descendents of this group
>>returned. Or, several distinct populations left Africa at different times.
>>The penultimate statement is a matter of recorded history. There was a huge
>influx of Arabs into North Africa and the Horn during the explosive growth of
>Islam. A similar dispersal of Jews also took place across North Africa. This
>is not speculation, unlike the migrations required by the eurogenetic theory.
The comments are irrelevant. Most of the migration events necessary
to explain the mtDNA tree probably occurred in excess of 20,000 years
ago, and thus are not part of recorded history (divergence in the
mtDNA lineages appears to have occurred over a span of 200,000 years).
The high mobility of recent humans may be a poor indicator of their
3. Extreme confusion about hominoid history. Jones has the same
confusions about hominoids that other correspondents displayed last
week, as he shows in his response to Larry:
>>The current residence of those species that are most closely related to the
>>genus Homo has nothing to do with your argument that "the molecular evidence
>>for an African origin of humans is rather certain.". . . For the purposes
>>of debate and discussion we will assume that Africa was the original home of
>>the genus Homo. There is no molecular data that either refutes or strengthens
>>that assumption and the validity of the assumption should not have any
>>affect on the Out-of-Africa discussion.
>>That's bull. The molecular data strengthens that assertion(not assumption!). It
>shows the the closest living relatives of homo are genera found only in Africa.
>If that is not strengthening afrogenesis, what is?
As I pointed out several days ago, the properties of the closest
living relatives of _homo sapiens_ would only be relevant to the
question of human origins if there were no paleontological evidence
about *extinct* close relatives or ancestors of _homo sapiens_ that
were already distinct from _pan_ (chimp) and _gorilla_. Early
representatives of the genus _homo_ (_habilis_ and _erectus_) arose
(about 2-3 MYA) in Africa from the australopithecines, which are
limited to South-Central Africa and thus are thought to have arisen
there (about 4 MYA). However, this is entirely irrelevant to our
present discussion, since the genus _homo_ distributed itself widely
BEFORE _homo sapiens_ became a prominent part of the fossil record:
that is, _homo erectus_ spread over Eurasia from
mediterranean europe to the far east about 0.5 to 1 MYA (ever heard of
"Java man"?). If we take _homo erectus_ to be the most likely
candidate for the species giving rise to _sapiens_, then Eurasia and
Africa are both candidates for the geographic location of this origin.
To repeat this point one more time: _h. erectus_ arose in africa,
spread itself throughout Africa, Southern Europe, and Asia, and
eventually gave rise to _h. sapiens_ (somewhere). That the chimp and
gorilla, distant cousins of the world-exploring _h. erectus_, were home-bodies
who never left Africa is a matter of no significance to the question at
hand, which is the origin of _h. sapiens_ from _h. erectus_.
(skippable opinions from here to end)
Jones also shows a disturbing inability to distinguish arguments from
>>I am not arguing that the data REFUTES the Out-of-Africa hypothesis...I am
>>simply trying to point out that it doesn't support it nearly as strongly as
>>most people believe . . . Please do not hesitate to correct me . . .
>>These remarks are curiously reminiscent of remarks I've read by old-guard
>paleontogists attempting to place the origin of genus homo outside of Africa.
>They are pathetic special pleading, nothing more.
You say you are a physicist, Jones, but I still think it would help
for you to investigate a little bit about how scientists work and what
science is. This would help you to distinguish statements that can be
evaluated on logical or factual grounds (such as "the data don't refute
hypothesis X, nor do they appear to support it strongly") from _ad
hominem_ arguments (such as "your statements are to me reminiscent of
statements made in the past by persons with questionable motives,
therefore they are irrelevant," an attempt at guilt by association).
If you just want to make _ad hominem_ arguments, that's your business,
but please do the rest of us a favor and include the word "flame" in
the title of any similar future posting that includes mainly
non-scientific arguments, so that we can ignore them if we so choose.
An inability to distinguish between these modes of discourse would be
a serious problem should you choose to continue in science.
Arlin at ac.dal.ca