Science 31 January 2014:
Vol. 343 no. 6170 pp. 471-472
News & Analysis

Neandertals and Moderns Made Imperfect Mates

Ann Gibbons | 6 Comments

Our extinct cousins left us some key genes, according to two studies of Neandertal DNA in living people, but much of their genetic legacy has been wiped out of modern genomes.

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How about this simple algorithm: Homo sapiens sapiens women think Homo sapiens neanderthalensis men look sexy. While sapiens men think Neandertal women look no-so-sexy. In this scenario, a Neandertal man might have perfectly fertile children with a sapiens woman, but only his sons (who have a Neandertal Y and no Neandertal X) would be able to attract sapiens mates. Neandertal X would be removed from the gene pool in two generations, with no need to invoke the pesky "mule" caveat.

I guess it's not a very scientific opinion, but in my perception European populations tend to view stockier, more muscular men as sexier, and conversely tend to view more gracile women as sexier. Maybe a lingering relic of ancient sexual preferences? Now that we can easily find out which Neandertal alleles people have, it's suddenly becoming a testable hypothesis.

Submitted on Mon, 02/17/2014 - 11:56

Adaptive changes during the past 10,000 to 5,000 years in genes associated with diet,immunity, skin pigmentation, and eye color were also recently reported in Olalde et al (2014):"Derived immune and ancestral pigmentation alleles in a 7,000-year-old Mesolithic European".

Metabolic and immunological challenges appear to be reflected in epigenetically-effected ecological adaptations. One adaptation appears to be the experience-dependent receptor-mediated ability to digest lactose.

That change and the other changes suggest an epigenetic effect of nutrient uptake was responsible for morphological and behavioral changes that could be sexually selected based on natural selection for food and its metabolism to species-specific pheromones that control the physiology of reproduction in species from microbes to man.

Submitted on Sat, 02/01/2014 - 22:35

"Hybrid males eventually become infertile before females, because men carry only one X chromosome, and so become infertile if the DNA on it is incompatible with their mates' X chromosome." Does this mean that the males themselves become infertile, i.e., incapable of producing young with any female, or that incompatibilities between the X chromosome of a particular male and his mate make that couple infertile as a couple (rather than either as an individual)?

Submitted on Sat, 02/01/2014 - 15:50

In my model, the epigenetic effects of nutrient uptake and the metabolism of nutrients to species-specific pheromones link de novo creation of olfactory receptor genes in different cell types to infertility when spermatozoa are no longer able to "sniff out" an "egg" in invertebrates: Elekonich and Robinson (2000) and vertebrates: Diamond, Binstock and Kohl (1996).

If you look at the problem in the context of what we portrayed about the conserved molecular mechanisms at the advent of sexual reproduction in yeasts, you may see the continuum of ecological adaptations that began with the nutrient-dependent pheromone-controlled chromosomal rearrangements that are required before sex chromosomes existed.

Submitted on Sun, 02/02/2014 - 14:34

"...DNA from a small number of Neandertal ancestors might have been swamped later by the sheer abundance of modern human DNA."

"Swamped" is an interesting word choice. Dr. Akey is senior author of the article with an abstract that states: " We estimate that approximately 73% of all protein-coding SNVs and approximately 86% of SNVs predicted to be deleterious arose in the past 5,000–10,000 years."

Creationists might take that to mean the "swamping" occurred after a flood of Biblical proportions, which appears to be somewhat consistent with Dobzhansky's "Creationist" belief. Clearly, however, that's only if you place his stated belief into the context of a shorter time frame, which enabled rapid ecological adaptations to occur via the nutrient-dependent pheromone-controlled physiology of reproduction, changes in base pairs, amino acid substitutions, and chromosomal rearrangements.

"I am a creationist and an evolutionist. Evolution is God's, or Nature's, method of Creation." -- Dobzhansky (1973) in "Nothing in Biology Makes Any Sense Except in the Light of Evolution"

Somewhat like Dobzhansky, perhaps, I have been overwhelmed by the amount of experimental evidence that suggests food is the ecological variable which is naturally selected. If so, the selection of nutrient-rich foods might lead to "swamping" via ecological adaptations sans the theory of mutation-driven evolution.

Submitted on Sat, 02/01/2014 - 13:10

These results appear to conflict with previous reports of biologically plausible non-random experience-dependent receptor-mediated species divergence due to ecological variation and adaptations. At least two of those reports were co-authored by Dr. Akey.

The adaptations show up in nutrient-dependent pheromone-controlled differences in cell types, which appear to be due to alternative splicings of pre-mRNA and amino acid substitutions, and the adaptations also show up in chromosomal rearrangements like those recently reported in sparrows with different morphological and behavioral phenotypes (see Estrogen receptor α polymorphism in a species with alternative behavioral phenotypes).

The differences in sparrows appear to be consistent with vertebrate-wide nutrient-dependent pheromone-controlled adaptations like those in the mouse-to-human example detailed in Kamberov et al (2013) and Grossman et al (2013) where a base pair change and single amino acid substitution showed up as differences in skin and hair, but also in teeth and mammary tissue in a population that arose during the past ~30,000 years in what is now central China.

Submitted on Thu, 01/30/2014 - 20:31