Is Aunt Irma visiting?

Men can get aggressive every month, particularly toward rugged, fertile looking chaps.

Rob Burriss, a biologist at the University of Liverpool, who led the study, said the behaviour reflected that of other primates: “Groups of animals, such as chimpanzees, can live quite happily together, but when a female is ready to mate the two dominant males within the group become rivals and fight for her attention.”

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