UBC Researchers Explain Why Females Are Better Off Choosing Unattractive Mates

In a research paper published in the Oct. 7 edition of the prestigious journal Science, UBC zoology professor Sarah Otto and graduate student Arianne Albert propose a model that explains why males in some species have extravagant displays for attracting females, while males in other species look just like females.

Many groups of animals, including humans, have an “XY” sex-determining system through which the father determines the sex of the offspring -- the offspring is female if it receives an X chromosome from the father, and vice versa. For these species, the chromosome on which flashy displays is coded will determine whether the sons or the daughters inherit the physical trait.

“If the genes coding for flashy displays are on the X, the genes from a sexy dad only appear in his daughters, making them visible to predators without improving their reproductive success, and thus favouring the evolution of preferences for dull males,” says Albert, lead author of the paper.

“Females in XY species -- including humans -- should therefore prefer bland males, because they produce more fit daughters.”

In other groups of animals (including birds), sex-determination is reversed. Females are ZW and males are ZZ, and therefore sex is decided by which sex chromosome (Z or W) is received from the mother.

“In these cases, when display genes are on the Z chromosome, the female is better off choosing a sexy mate, because the dad passes the Z to the sons who are thus more attractive,” says Otto.