Anthropology.net

Human mating systems are mediated by many different variables, from cultural preferences to religious alignments. In some places, people marry and mate within their class or ethnic group. But there are more subtle, almost subliminal conditions behind mating that often affect the outcome of genetic variation and evolution. While I was out of the country, a paper was published in PLoS Genetics which outlined one of these conditions — mate choice and the major histocompatibility complex.

If you haven’t taken an immunology or molecular biology course, you may not know what the major histocompatibility complex (MHC from now on) is. The MHC is the most gene dense region of the mammalian genome and encodes for a lot of proteins act which act as signposts on the cell. These proteins are a crucial part of the autoimmune system. These signposts identify cells as self or foreign to the immune system, ultimately making MHC’s a critical part of disease-resistance. As Dienekes summarized, the evolutionary implications are pretty profound,

“couples dissimilar in [MHC genotype] will produce heterozygous children that will be more capable of fighting disease.”

The three authors of, “Is Mate Choice in Humans MHC-Dependent?,” asked whether or not couples differ more or less in the MHC region of the genome they do across the entire genome? Their testing employed genome-wide genotype data and HLA types in a sample of Yoruban and a sample of European American couples. This allowed them to distinguish MHC-specific effects from genome-wide effects. The group examined whether husband-wife couples were more MHC-similar or MHC-dissimilar in comparison to random pairs of individuals.

Surprisingly, the African couples were not more MHC-similar nor MHC-dissimilar. But across the genome, they were more similar than random couples. How could this be? This could possibly be due to social factors, i.e. mating with genetically close individuals that are within social units, rather than with individuals from the entire population.

European American couples, however, were predominantly MHC-dissimilar. They were drastically so in comparison to the genome, supporting the hypothesis that the MHC influences mate choice in this population. Does this mean that there’s been some sort of evolutionary pressure for Europeans to have more heterozygosity at MHC loci? I’d venture to say yes, epidemics like the Black Plague severely affected European populations but that’s not to say African’s have been disease free. As you may know malaria has constantly been a problem. More studies need to be conducted in other African populations with different mating patterns to fully consider if biological traits like MHC genotype play a significant role beside social traits in the process of mating.

Raphaëlle Chaix, Chen Cao, Peter Donnelly, Molly Przeworski (2008). Is Mate Choice in Humans MHC-Dependent? PLoS Genetics, 4 (9) DOI: 10.1371/journal.pgen.1000184

Zooarchaeology is an anthropological sub-discipline which focuses on studying animal remains from archaeological sites. Animal remains can tell us a lot of about prehistoric peoples’ diets and behavioral tendencies as well as the ecological makeup of the area. A new PNAS paper investigates the zooarchaeological record of two Neandertal sites in Gibraltar, Vanguard and Gorham‘s Caves.

The paper, “Neanderthal exploitation of marine mammals in Gibraltar,” is authored by some familiar names such as Chris Stinger and J.C. Finalyson and Nick Barton, and the major conclusion is that the presence of mollusks, seal, dolphin, and fish from such sites suggests that Neandertals exploited a wide variety of foods — hammering yet another nail in the coffin of the Neandertals were dumb cavemen train of thought. John Hawks and Dienekes have both written that this research is yet another line of evidence in the modernization of Neandertal behavior.

The cave sites are part of the Gibraltar Caves Project, which began in 1994. Annual excavations followed the year after. The sites are located on the southeast side of the Rock, on Governor’s Beach. As far as I can tell, GPS coordinates were not provided. I’ve tried to track down the exact location of the sites but have found conflicting information. But the BBC has provided an image of the sites, by way of the Gibraltar Museum. The two sites are adjacent to each other and the Gibraltar Museum has dutifully also provided a prehistoric view of the sites when sea levels were much lower:

Gorham's & Vanguard Caves on Governor's Beach, Gibraltar.

Gorham’s Cave site indicates three distinct occupations. There’s an Upper Palaeolithic occupation with dates spanning 26-30,000 years before the present (BP). There’s another distinct layer containing the youngest Middle Palaeolithic and dated at around 31-32,000 BP, and a third, older Middle Palaeolithic layer which is underneath. This older layer is dated to 45,300 ± 1,700 years BP. Vanguard Cave shows similar patterns with radiocarbon dates of 45,000 years BP and similar lithic assemblages.

Cut marks from a Mediterranean Monk Seal finger bone found in Vanguard Cave

Vangaurd Cave has yielded evidence of Mediterranean monk seal (Monachus monachus) phalanxes with cut marks and lots of mollusk shells. The minimum number of mollusks found isn’t provided but the authors do say that a particular layer was dominated by mollusk shells. Additionally the concentration of knapping debris and Mousterian stone tools, along with a hearth, from this layer suggest that Neandertals were having a prehistoric cioppino feast.

Additional remains of ibex, red deer, boar, bear, along with dolphins birds, tortoises indicate that these prehistoric people were exploiting a wide variety of food sources. Roughly 50% of the animal remains were cut or burned, and a lot of the rest show percussion marks and fractures. Compared to Neandertals from Northern Europe, who sustained a diet of big game meat such as mammoth, deer and horse, these guys from Governor’s Beach had a different diet. Stringer told the BBC that these caves tell us that we can’t generalize Neandertals.

C. B. Stringer, J. C. Finlayson, R. N. E. Barton, Y. Fernandez-Jalvo, I. Caceres, R. C. Sabin, E. J. Rhodes, A. P. Currant, J. Rodriguez-Vidal, F. Giles-Pacheco, J. A. Riquelme-Cantal (2008). From the Cover: Neanderthal exploitation of marine mammals in Gibraltar Proceedings of the National Academy of Sciences, 105 (38), 14319-14324 DOI: 10.1073/pnas.0805474105