These results provide some support for an association between genetic diversity and a measure of general, everyday health in humans. We found a small, but significant, effect of nonMHC genetic diversity, measured as standardized mean-d2, on health. Individuals with greater nonMHC-d2 reported significantly fewer symptoms over a four-month period than less diverse individuals, with nonMHC-d2 accounting for 3% of the variance in health. This relationship suggests that the previously observed male preferences for the faces of females with high levels of nonMHC-d2 would be adaptive for obtaining a healthier mate [46].PLoS ONE doi:10.1371/journal.pone.0006391
Does Genetic Diversity Predict Health in Humans?
Hanne C. Lie et al.
Abstract
Genetic diversity, especially at genes important for immune functioning within the Major Histocompatibility Complex (MHC), has been associated with fitness-related traits, including disease resistance, in many species. Recently, genetic diversity has been associated with mate preferences in humans. Here we asked whether these preferences are adaptive in terms of obtaining healthier mates. We investigated whether genetic diversity (heterozygosity and standardized mean d2) at MHC and nonMHC microsatellite loci, predicted health in 153 individuals. Individuals with greater allelic diversity (d2) at nonMHC loci and at one MHC locus, linked to HLA-DRB1, reported fewer symptoms over a four-month period than individuals with lower d2. In contrast, there were no associations between MHC or nonMHC heterozygosity and health. NonMHC-d2 has previously been found to predict male preferences for female faces. Thus, the current findings suggest that nonMHC diversity may play a role in both natural and sexual selection acting on human populations.
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"These results provide some support for an association between genetic diversity and a measure of general, everyday health in humans".
ReplyDeleteSo, in spite of what many people here claim, inbreeding becomes a problem even in very large populations.
Just to carry on a little:
ReplyDeleteD. S. Falconer (1964), the author of my old genetics textbook ("Quantitative Genetics"), wrote, "The phenomenon of heterosis is simply inbreeding depression in reverse".
For any of you who might like to brush up on this idea that heterosis and inbreeding are simply opposite sides of the same coin I've attempted to explain it all here:
http://humanevolutionontrial.blogspot.com/2009/06/human-evolution-on-trial-hybrid-vigour.html
The essay is a little long and detailed so I'd be inclined to print it off, relax when you have a moment to spare and read it, perhaps invite your students to take on the roles of 'defence', 'prosecution' or 'jury'.
The relevance of the topic is revealed when we try to answer the question: "is the modern haplogroup pattern the product of a single, rapid expansion from a single point in Africa, or is it the product of an irregular series of expansions through pre-existing populations?"
For a start, surely it's unlikely that the original modern human population consisted of just two women, one being mtDNA L0 and the other L1-6. These two haplogroups are obviously simply the survivors of a population that had originally contained many other haplogroups. So how widespread was the population?
The sub-Saharan mtDNA expansion was probably at least partly through pre-existing populations. The total modern human genome is greater than just that contained by just the two women L0 and L1-6, along with any male partners they may have had. Anyway the haplogroups appear to have become spread widely through South and East Africa (L0), East Africa (L5), East and West Africa (L1), and West Africa (L2) long before any modern humans mtDNA lines had left Africa.
The mtDNA pattern within Africa suggests a subsequent major expansion, probably from East Africa, over much of the already occupied region: L3 and 4 through East Africa, West Africa, North Africa and the world, and L6 in Yemen.
So again we're down to just two women, M and N, containing all future human genetic variation?