Diffusion wave out of Africa

[Mikey Brass]

Current Anthropology, December 2002
A Diffusion Wave out of Africa: The Mechanism of the Modern
Human Revolution? by Vinayak Eswaran

Abstract
This paper proposes that the worldwide transition to an anatomically modern human form was caused by the diffusive spread from Africa of a genotype—a coadapted combination of novel genes—carrying a complex genetic advantage. It is suggested that the movement out of Africa was not a migration but a “diffusion wave”—a continuous expansion of modern populations by small random movements, hybridization, and natural selection favoring the modern genotype. It is proposed that the modern genotype arose in Africa by a shifting-balance process and spread because it was globally advantageous. It is shown that the genotype could have spread by directionally random demic diffusion, but only under conditions involving a low rate of interdeme admixture (“interbreeding”) and strong selection. This mechanism is investigated using a quantitative model that suggests explanations for many puzzling aspects of the genetic, fossil, and archaeological data on modern human origins. The data indicate significant genetic assimilation from archaic human populations into modern ones. A morphological advantage of the modern phenotype—possibly reducing childbirth mortality—is proposed as the cause of the transition. The evidence of this and previous human “revolutions” suggests that the shifting-balance process, proposed by Sewall Wright, was particularly important in human evolution —possibly because human populations had a small-deme social structure with low interbreeding rates that allowed it to operate. This may explain the relative uniqueness of human evolution.

[rich]

Hi Mike,
good call on this link,
I somehow got hold of this paper a year or so back, in perhaps a draft form, I can't recall, It is a well written piece and certainly stirs the grey matter. I recommend the read to all.
What also is stunning is the fact that Vinayak Eswaran resided at the time of the paper I have hold of, at the Dept of mechanical engineering in the Indian Institute of tech in Kanpur , India, and therefore the research IMHO has been undertaken on a fresh un blinkered path.
As I remember, he puts forward a diffusion wave theory of movement of genes carrying the modern form outwards from its source but not fuelled by a movement of individual as such, more a diffusion of modern genes gradually infiltrating into the next local archaic pop in the way of the wave, and this then "taking them over", only to continue to the next pop. It also sees a way of explaining certain anomolies within the anthro record. Read and discuss please everyone interested.
Rich.

[Dale Hoogeveen]

Hi Mike,
good call on this link,
I somehow got hold of this paper a year or so back, in perhaps a draft form, I can't recall, It is a well written piece and certainly stirs the grey matter. I recommend the read to all.
What also is stunning is the fact that Vinayak Eswaran resided at the time of the paper I have hold of, at the Dept of mechanical engineering in the Indian Institute of tech in Kanpur , India, and therefore the research IMHO has been undertaken on a fresh un blinkered path.
As I remember, he puts forward a diffusion wave theory of movement of genes carrying the modern form outwards from its source but not fuelled by a movement of individual as such, more a diffusion of modern genes gradually infiltrating into the next local archaic pop in the way of the wave, and this then "taking them over", only to continue to the next pop. It also sees a way of explaining certain anomolies within the anthro record. Read and discuss please everyone interested.
Rich.

Consider that the concept of diffusion wave may be extremely accurate, but that it is not signaling the spread of genetic lineages, but rather the spread of a condition that is producing similar phenotypic expression;  such as possibly a cultural trait or behaviour that allows similarly appearing gracile traits by culturally counteracting selective needs for robusticity.  Such a condition might be very subtle if for example it simply allowed for increased survival of a more fragile (ie more gracile - ?) child.  (I expect that childhood mortality is likely to be a more definite selective pressure toward robusticity than adult mortality.)

That would make gracility more of a set of similar responses than a consistant genetic trait, which seems to me to be a more accurate basic understanding of the condition anyway.

Dutch