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A recent study led by the University of Eastern Finland explored sexual selection in humans by investigating whether female odor-based mating preferences could predict how compatible male and female gametes are.

Major histocompatibility complex (MHC) genes are known to mediate sexual selection both at the individual and gamete level. Previous studies have shown that perceived body odor attractiveness is strongly affected by these genes. However, it has remained unclear whether MHC-based mating preferences are consistent prior and after copulation.

To study this, the researchers performed a full-factorial experiment where 10 women first ranked the attractiveness and intensity of body odor samples collected from 11 men, followed by an analysis of whether female body odor preferences in these same 110 male–female combinations predicted sperm performance in the presence of follicular fluid. The results are in the journal Heredity.

"We are very grateful to all the participants who enabled this study. To perform the odor collection in a reliable manner, men received very detailed instructions that they successfully followed. We are very confident that we were able to catch the characteristics of each individual body odor. Additionally, women committed to testing their ovulation to ensure that odor rating occurred during their fertile window," says Annalaura Jokiniemi, Ph.D., the first author of the study.

An analysis of the total MHC similarity—including both classical and non-classical MHC genes—of the male-female combinations showed that women preferred the body odors of MHC-similar men, but that sperm motility was positively affected by the MHC dissimilarity of the male–female combinations.

"Women showed a preference for the body odors of MHC-similar men. However, sperm from MHC-dissimilar men exhibited higher motility when exposed to female follicular fluid, suggesting that the most attractive males may not necessarily always be the most optimal partners in terms of fertilization success," Professor Jukka Kekäläinen of the University of Eastern Finland notes.

The results indicate that individual and gamete-level mate choice processes may in fact act in opposing directions, and that gamete-mediated mate choice may have a definitive role in disfavoring genetically incompatible partners from fertilizing oocytes.