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It could also be an emergent property of the inter-breeding. Maybe those particular genes are fine in Neandertals, but combined with some Cro-Magnon genes leads

It could also be an emergent property of the inter-breeding. Maybe those particular genes are fine in Neandertals, but combined with some Cro-Magnon genes leads to depression. I know that if you interbreed a lion and a tiger to make a "liger" the resulting hybrid grows to be larger than either lions or tigers; something similar could be happening here.

thaumasiotes 10y ago
Take this in the spirit of fun facts, but the liger largeness phenomenon is not well described by the analogy "Maybe those particular genes are fine in Neandertals, but combined with some Cro-Magnon genes leads to depression". Liger largeness (and the word "liger") is specific to the offspring of a male lion and a female tiger; the offspring of a male tiger and a female lion (a "tiglon" or "tigon") doesn't grow so large. What's going on is that lions rely on their mates being other lions -- male lions imprint their sperm in a way that promotes growth of the cub (which is a drain on the lioness's milk production) and female lions imprint their eggs so as to inhibit growth. It's not an interaction between lion genes and tiger genes that produces excessive growth, it is the male-imprinted lion genes failing to meet the female-imprinted genes they've evolved to rely on. The same phenomenon (in terms of genetic arms race between the sexes -- it's phenotypically different) occurs in humans under the names Prader-Willi syndrome (maternal genes fail to meet paternal resistance) and Angelman Syndrome (other way around).
danieltillett 10y ago
Just to nit pick Cro-Magnon people were the Eurasians that populated Europe after the hybridisation event(s) between Neanderthals and AMH. We know from sequencing studies that they had a higher level of Neanderthal alleles than modern Europeans. Their larger brain size suggests a liger-like overshoot in brain growth given the constraints of the birth canal. I suspect Cro-Magnon women had an even more terrible time in childbirth than modern women.

thaumasiotes 10y ago

Take this in the spirit of fun facts, but the liger largeness phenomenon is not well described by the analogy "Maybe those particular genes are fine in Neandertals, but combined with some Cro-Magnon genes leads to depression". Liger largeness (and the word "liger") is specific to the offspring of a male lion and a female tiger; the offspring of a male tiger and a female lion (a "tiglon" or "tigon") doesn't grow so large. What's going on is that lions rely on their mates being other lions -- male lions imprint their sperm in a way that promotes growth of the cub (which is a drain on the lioness's milk production) and female lions imprint their eggs so as to inhibit growth. It's not an interaction between lion genes and tiger genes that produces excessive growth, it is the male-imprinted lion genes failing to meet the female-imprinted genes they've evolved to rely on. The same phenomenon (in terms of genetic arms race between the sexes -- it's phenotypically different) occurs in humans under the names Prader-Willi syndrome (maternal genes fail to meet paternal resistance) and Angelman Syndrome (other way around).

danieltillett 10y ago

Just to nit pick Cro-Magnon people were the Eurasians that populated Europe after the hybridisation event(s) between Neanderthals and AMH. We know from sequencing studies that they had a higher level of Neanderthal alleles than modern Europeans. Their larger brain size suggests a liger-like overshoot in brain growth given the constraints of the birth canal. I suspect Cro-Magnon women had an even more terrible time in childbirth than modern women.