Out of Africa

Jones Maxime Murphy morphy at cco.caltech.edu
Tue Nov 19 17:42:02 EST 1991


lamoran at gpu.utcs.utoronto.ca (L.A. Moran) writes:


>This is an interesting point but I don't see why it is relevant. Let's assume
>that Homo sapiens sapiens arose in Eurasia and that the original population
>split in two with half migrating to Africa. At some later point in time
>another group from Eurasia also moved to Africa. In fact, there may have been
>several such incidents over time.

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, can you construct an Out-of-Africa senario that is so obvioulsy more
>reasonable and more simple? Any senarios that I can think of still require
>many migrations between continents. For example, 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.

>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. You have focused on one of my key objections. With all 
>due respect I do not believe that you have thought skeptically about what 
>you are saying and why it makes the Out-of-Africa hypothesis "rather certain".
>However, I admit to being somewhat nervous about making statements such
>as this in case I have missed something obvious. Please do not hesitate to
>correct me if my logic is flawed.

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.


>This is the same point that you raised before but it gives me an opportunity
>to point out that Cavelli-Sforza's data shows a clean separation between
>African and non-African populations while Wilson's data does not seem
>reasonable to me.

Wilson's data is old, and from a far smaller sample, including the very mixed
Afro-Americans.

> Even if your logic was correct (which it isn't IMHO) I
>would be reluctant to rely so heavily on such data. At the risk of getting
>off on a tangent how does one explain the wide separation of some populations
>that we expect to cluster together on the dendrogram? How does one explain
>data that shows that Australians are more closely related to African
>pygmies than to Asians?

The data speaks for itself. It also shows that the Inuit are more closely
related to Malays than to Icelanders! Wow. This is specious innuendo at it's 
worst.

>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.". This illustrates one
>of the other points that I was trying to make in my original posting namely
>that molecular biologists often get confused over the difference between
>the origin of the GENUS Homo and the origin of the SPECIES Homo sapiens.

Not so. This whole issue came up because you questioned the rooting of the 
tree, as I recall.

>It also seems to be quite commmon to use non-genetic arguments, as Keith
>does, to support the molecular data instead of the other way around. 

Why shouldn't corroborating data be cited, whatever the source?

>(The data in question here is the current home of gorillas and chimps. It
>doesn't seem likely to me that I can discover this by looking at my sequencing
>gels! We have to rely on field biologists...the ones that actually know what
>these organisms look like. The real data would be the fossil evidence that
>demonstrates that the earliest fossils of gorillas and chimps are from
>Africa. If the earliest fossils were from central Asia then it would not
>matter what the field biologists had to say about present day distribution.)

Well the earliest fossils are from Africa, not from Central Asia.

>Let's restrict discussion of the Out-of-Africa hypothesis to the RECENT 
>origin of Homo sapiens sapiens and the possibility that this population
>replaced existing populations of Homo sapiens by spreading from an African
>center. This event is postulated to have occurred about two hundred thousand
>years ago or less. Alternatives to this hypothesis are that modern humans 
>arose somewhere else, especially that they arose gradually throughout the 
>inhabited world by evolving from the indigenous populations. 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?
Jones
-- 
:)



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