Choosing a Mate by Smell

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A new study shows that mice pass on genetic information through their urine

According to a scientific theory, so far unproven, animals and humans can smell a particular type of genes linked to the immune system of potential mates. These genes, called MHC (major histocompatibility complex), as the theory goes, influence an animal’s or human’s choice of mate. According to another unproven theory, information on MHC genes is passed on through MHC peptides—which are presented by MHC genes at their surface when interacting with the immune system’s killer cells.

So far no research has come close to proving these theories. However, a new study conducted on mice and published in Nature Communications offers new insights into these theories. Researchers from University of Tübingen in Germany were able to identify an MHC peptide in mouse urine that indicates a corresponding MHC gene. But apart from the MHC peptide, they also found hundreds of other peptides that had no connection with MHC genes, in mouse urine. The concentration of these peptides was a million times higher than that of the MHC peptide. The researchers say that the peptides, both MHC peptides and others, can activate specific olfactory cells in mice, and that they allow the mice to map most of their fellow mice’s genes. MHC peptides have yet not been detected in human urine, saliva or sweat.

The researches claim that their research shows that it is not the smell of immunogenes alone, as previously believed, but the olfactory similarities and differences in the overall genome that play an important role in mate selection. The authors write in the journal: ‘By analysing the identity and genomic origin of naturally occurring peptides in mouse urine, we have discovered multiple, partly overlapping peptide pools that contain distinct types of information related to genomic individuality... Hence, the emerging picture is a complex scenario in which multiple peptide families together with previously characterized MUPs, formylated and maternally inherited peptides (not yet shown to exist in urine) and possibly other yet undiscovered ligand (a type of molecule) families link the genotype of an individual with nasal chemoreception mechanisms.’