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Human evolution: Neanderthal genes led to infertility?

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Neanderthal museum diorama, Croatia/ Max Planck Institute

It wasn’t enough the Neanderthals gave us cancer, they also gave us infertility

Not all of the Neanderthal genes are beneficial. Sankararaman and Reich found that our Neanderthal inheritance includes several genes that make us susceptible to diseases including type 2 diabetes, lupus and Crohn’s disease.

Some of the genes, meanwhile, appear to have led to fertility problems. For instance, Sankararaman found that the X chromosome is almost devoid of Neanderthal DNA. This suggests that most Neanderthal DNA that wound up on the X chromosome made the bearer less fertile – a common occurrence when related but distinct species interbreed – and so it quickly disappeared from the human gene pool. “Neanderthal alleles were swept away,” says Sankararaman.

Maybe. Can we spell S-T-R-E-T-C-H?

According to another recent study,

A substantial fraction of the Neanderthal genome persists in modern human populations. A new approach applied to analyzing whole-genome sequencing data from 665 people from Europe and East Asia shows that more than 20 percent of the Neanderthal genome survives in the DNA of this contemporary group, whose genetic information is part of the 1,000 Genomes Project.

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Toldjah. Some people never forgave the “Neaderdunce” for marrying into the family. They just keep throwing mud, figuring some of it will stick. 😉

It occurs to me that should Neanderthal tribes decide that male infants who "looked different" must be killed, whilst female infants who "looked different" could live, wouldn't that alone be one possible way that the "male hybrids were infertile" ie maybe they were infertile b/c did not live long enough to reproduce? Another curiosity: why do people seem to think the Neanderthal was less intelligent than other humanoids, when they clearly had much bigger brain cases? There is also the tendency to model Neanderthal artistic-recreations as having pitted skin, scraggy hair, frowning faces, etc. time and again, whilst models of other humanins have clear skin and are usually modeled with hair "neatly pulled back from their faces." Why do you think this is so? Neanderthals were tool users and hunters who likely had enough skill to make neat hide or animal-skin wraps for clothing and foot covers,(and not having scraps hanging down to get caught in bushes and having footgear in cold climes would have an advantage for them) yet always they are interpreted to be dressed looking greatly bedraggled and barefoot. People who believe Neanderthals "gave us cancer or gave us diabetes" must have very small brain cases, indeed. If this were so, no one amongst those subsaharan folks would ever get diabetes or cancer, right? As my name suggests, just curious... curiousme
DRC The neanderthal genome paper has a lengthy discussion of the samples form which the data came, the challenge of using highly degraded DNA (more like 130,000 years old) and the techniques used to ensure contamination from modern DNA is avoided. Briefly, 600 years isn't an absolute half life for DNA, it's the result of one study in one set of conditions. DNA will survive longer in cooler scenarios (the neandethal genome is from a Croatian gave, the current record for recovered DNA is form Siberia). Evenso, the recovered DNA is very short (around 200 bp) and massively outnumbered by contemporary contamination. You can exclude microbial DNA easily enough, but prevent modern human contamination requires great care in the field and laboratory. You can't really use the degree to which DNA is degraded as a clock, as there is just too much variance in the degradation form one site to the next. We only have a few sites form which really good records can be obtained to calibrate such a clock, and those sites don't have neanderthal remains. In any case, all these bones come for archaeological layers which can be accurately dated with carbon-dating and the like. wd400
Honest question here: How did they sequence a Neanderthal genome? According to the paper cited (and other references), Neanderthals died out about 30,000 years ago. If DNA has a half-life of about 600 years as cited elsewhere on this site, where did they find enough Neanderthal DNA or RNA to sequence genes from? (if I do my math right (not likely), 30000 years is around 50 half-lives for DNA, which means approx 2^-50th of the original DNA is left?) Just curious - the papers never seem to talk about where they get the Neanderthal genome from to sequence. Corollary question: Given the ability to calculate the half-life of DNA, the length of DNA in humans/Neanderthals, and the length of DNA recovered from remains, shouldn't scientists be able to calculate the age of remains that way? If the recovered strand length > few %, shouldn't that mean the remains aren't really that old? (e.g. 4K years would be approx. 1% left?) I realize my ignorance is showing, but if someone can provide/link an answer, I'd appreciate it. drc466
Why do think this hypothesis is such a "stretch"? Decrease fertility is very common in hybridization, and hybrid male sterility has been shown to arise from x-chromosome genes in several species. In this paper the authors show regions lacking in Neanderthal ancestory are more likely to be expressed in testes. wd400

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