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T R A C I N G . H U M A N . W A N D E R I N G S
NEANDERTHALS AND CROMAGNONS
Andrew Gyles
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- Interbreeding of Neanderthals and modern humans: Males can beget more children than females
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Interbreeding of Neanderthals and modern humans (Cromagnons): loss of Neanderthal mitochondrial DNA if the husbands joined the race of their wives
Most anthropologists seem to accept the conclusion of molecular evolutionists that the recently obtained sequences of Neanderthal mitochondrial DNA prove that Neanderthals and Cromagnons did not interbreed, even though they lived close together in some places for thousands of years.
This conclusion is not necessarily correct. If there were some interbreeding, and if it were generally the case that the husband moved to join the race of his wife, the Neanderthal mitochondrial DNA would have disappeared from the European gene pool in the long run, but Neanderthal nuclear DNA would have been permanently taken into the European gene pool.
This would have happened because only females transmit mitochondrial DNA to their children. If Cromagnon husbands of Neanderthal women moved to live with the Neanderthals their children would have had Neanderthal mitochondrial DNA, and half of their nuclear DNA would have come from their Cromagnon father. But, as we know, in the long run the Neanderthals died out, and the descendants of such first-cross children would have died out with them. If Neanderthal husbands of Cromagnon women moved to live with the Cromagnons their children would have had Cromagnon mitochondrial DNA, and half of their nuclear DNA would come have from their Neanderthal father. As we know, the Cromagnons did not die out, and so the descendants of the latter first-cross children would not have died out.
This is a hypothetical case because we do not know whether husbands moved to live with their wives, or wives moved to live with their husbands, or whether there was no traditional rule and it was just a matter of individual choice. But the hypothetical case described above might have happened generally enough to ensure that a substantial number of Neanderthal nuclear genes, but no Neanderthal mitochondrial genes, did persist in the European gene pool.
Published 20 April 2000. © Andrew Gyles
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Interbreeding of Neanderthals and modern humans (Cromagnons): how to prove it by molecular genetics
If Neanderthals and modern humans (or Cromagnons, as some authors prefer to write) interbred, the children of Cromagnon mothers would all have Cromagnon mitochondrial DNA (mtDNA). The children of Neanderthal mothers would all have Neanderthal mtDNA.
If the mtDNA of fossils that look like first-generation crosses between Neanderthals and Cromagnons is sequenced some of the sequences will be Cromagnon and some will be Neanderthal (assuming that both sexes of both human types interbred). Therefore the first molecular geneticist to find Cromagnon mtDNA in a fossil that looks predominantly Neanderthal but with some Cromagnon admixture will be the first to have proved that the two human types did interbreed.
Published 27 January 2000. © Andrew Gyles
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Interbreeding of Neanderthals and modern humans: Males can beget more children than females
If male Neanderthals mated with female modern humans the offspring would have inherited mitochondrial DNA only from the female modern humans.
I pointed out in an earlier article (see below) that this mating was more likely than the mating of male modern humans with female Neanderthals because of the preference of human males for gracile females, and because of the preference of human females for robust males.
If male Neanderthals were sexually attracted to female modern humans and mated with them polygamously they might each have fathered several, or many, children in a year. But even if female Neanderthals mated with male modern humans (which, as I suggested earler, was unlikely) each could have conceived and given birth to only one child a year (two if twins).
A further consideration is that male Neanderthals were bigger and stronger than male modern humans. A male Neanderthal could have courted a female modern human with impunity. A male modern human might have courted a female Neanderthal with rather less confidence that he could have defended himself against her male Neanderthal wooers and her male Neanderthal relations.
These facts provide further support for the view that Neanderthals and modern humans might have interbred with no (or little) transmission of Neanderthal mitochondrial DNA.
Published 24 January 2000. © Andrew Gyles
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Interbreeding of Neanderthals and modern humans without transmission of Neanderthal mitochondrial DNA: effect of mating preferences
If male Neanderthals mated with female modern humans the offspring would have inherited mitochondrial DNA only from the female modern humans.
This mating was more likely than the mating of male modern humans with female Neanderthals because of the preference of human males for gracile females. It was also more likely because of the preference of human females for robust males.
The mating of a female Neanderthal with a modern human male was unlikely because she would find him gracile and he would find her robust.
If the mating preferences of Neanderthals were similar to those of modern humans, which are well documented, the sequencing of mitochondrial DNA from Neanderthal fossil bone will not indicate whether Neanderthals and modern humans did or did not interbreed. The work of M. Krings et al, for example, shows only that female Neanderthals did not mate very often with male modern humans.
References: Krings, M. et al. Cell 90, 19-30 (1997).
Ward, R. & Stringer, C. Nature 388, 225-226 (1997).
Published 21 January 2000. © Andrew Gyles
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