out of africa

GRAZIANO PESOLE PESOLE at MVX36.CSATA.IT
Fri Nov 22 10:48:00 EST 1991


I wish to contribute to the discussion with just some points:

- the molecular clock hypothesis MUST be assumed in order to state that
  larger genetic differences within Africans and between Africans and other
  peoples means the African origin for humans.

- Almost all genetists and paleontologists agree on the African origin of
  humans. The competing models are: 1) the "Garden of Eden" for which
  modern populations are thought to have originated from a common mother who
  lived in Africa about 200,000 years ago, from which originated all modern
  populations. 2) The Multiregional Model according to which modern
  populations originated independently in different areas of the world.

To solve this intricate issue a very accurate determination of the time of
divergence of the deepest root of human mtDNAs is needed.
To do this one should consider that the regulaty region of mtDNA, which has
been used in all the sequence analyses is not subjected to neutral
evolution, but strong functional constraints act on some regions (see:
Saccone et al., The main regulatory region of mammalian mitochondrial DNA:
structure-function, model and evolutionary pattern. J. Mol. Evol. 33:83-91,
1991).
In this regard I think that the time estimates of Vigilant et al. (Science,
1991) are not accurate. If the divergence time estimated for the deepest
root of humans become larger, the scenario of human origin can completely
change.

Graziano Pesole


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