In a recent paper out in PLoS Genetics titled Is Mate Choice in Humans MHC-Dependent? (Chaix et al. 2008) the authors use genetic data to see if the MHC locus is more or less similar between spouses than the rest of the genome. Selection of mates on the basis of MHC locus differences is something that’s been shown in a bunch of animal studies, but it’s still unclear how it works in humans. You may have heard of the studies where women who smelled used men’s undershirts preferred the smell of men with different MHC loci, but some studies have provided contradictory results.
To briefly explain: Genes in the MHC locus are involved in recognizing pathogens. Therefore it is likely advantageous to have more differences between the two alleles at this loci to have a better chance of recognizing more pathogens. Several studies with different animal models have shown a preference for mates that have less similar MHC loci.
What Chaix et al. find is that among European Americans the MHC locus is less similar between spouses than the rest of the genome. Suggesting that we, like mice, prefer to mate with people that have different MHC loci from our own. Notably Chaix et al. don’t find this pattern at all in the Yoruban African samples they examine which makes for some interesting discussion about possible cultural influence or diversity issues. While I don’t know enough about population genetics to confidently say how strong their results are, they sound reasonable to me.
I love the the way people are increasingly using human genomic sequence data to piece apart issues of evolution and demographic history. I also love that this paper is short and well written enough for someone who knows little about population genetics (eg. me) to understand.
Chaix R, Cao C, Donnelly P (2008) Is Mate Choice in Humans MHC-Dependent? PLoS Genet 4(9): e1000184. doi:10.1371/journal.pgen.1000184
Why do a limited number of great themes and archetypes pervade the sagas of so many different and apparently unrelated peoples?
- Stories spread by learning, and telling, from a single source, and cultures are not nearly as independent as we assume.
- The evolutionary structure of the mind, as shared by all people, encodes archetypes that channel our independently invented stories along similar pathways, no matter what culture invents the tale.
- Gould, among others, suggests a third possibility. Our stories about sequential stages are such because we know no other way to make such stories go.
We view the stages of our sequences either as increments of progress (simple to complex) or as steps in refinement (ill-formed and inchoate to well-separated and sharply differentiated). The model for the first is simple addition (each step adds new features and becomes more complex); for the second, differentiation (all bits of complexity exist from the start, but only as potential within an initially homogenous mass). The “march” of the amoeba to human (a false description of evolution) falls into the first category of addition; Michelangelo’s assertion that the final statue already exists in the initial block of marble (waiting for liberation by the sculptor) represents the second category of differentiation. These two primal explanations are only different aspects of a single sequence of objects.
Most of the Creation myth in Genesis 1 reads as a tale of addition—first God creates the earth, then plants, fishes, terrestrial beasts, or tetrapods, and finally exalted us. However, a more literal interpretation of the words suggests differentiation as the intended theme. From an initial formless chaos, God makes a series of progressively finer separations: light from darkness, earth from sky, land from sea, coalescence of sun and moon as sources of light, “bringing forth” of living from the earth.
Much of the research I do at the NIH involves developmental biology and embryology, which features both stories as start-points for the great theories that have defined the area of study since its inception. In a famous19th century debate, Ernst Haeckel’s (a comparative embryologist) recapitulation theory (“ontogeny recapitulates phylogeny”)—following the model of addition—viewed the embryo as growing ever more complex by repeating the adult stages of ancestors in an evolutionary series. Von Baer’s contrary reading—following the model of differentiation—interpreted the embryo as expressing its taxonomic status ever more finely through development: first, one can tell the creature will become a vertebrate, then a mammal, then a primate, then a human.
As a side note: Haeckel was famously wrong (as cool as it might be, human embryos do not have gills).
In his book Rocks of Ages: Science and Religion in the Fullness of Life, Gould said he always viewed the primal stories of addition and differentiation as our literary biases imposed upon nature’s greater richness.
In a recent paper out in PLoS Genetics titled Is Mate Choice in Humans MHC-Dependent? (Chaix et al. 2008) the authors use genetic data to see if the MHC locus is more or less similar between spouses than the rest of the genome. Selection of mates on the basis of MHC locus differences is something that’s been shown in a bunch of animal studies, but it’s still unclear how it works in humans. You may have heard of the studies where women who smelled used men’s undershirts preferred the smell of men with different MHC loci, but some studies have provided contradictory results.