Love at first smell | Science Blog. The Major Histocompatibility Complex is part of the immune system, but in many species, it also serves to identify mate odors which indicate a suitable match. Since MHC is highly polymorphic, close relatives have similar MHC, while more distant relatives will be more different. MHC recognition minimizes inbreeding.
This research shows that MHC reacts with peptides in body odors from stickleback fish. The author says
Since sticklebacks use the same molecules to communicate information about their immune system as other vertebrates, this experiment can be assumed to be important for many animals, including humans.Common descent, evolutionary hypotheses.