Hormonal contraceptives alter lemur odours

New research published this week in Proceedings of the Royal Society B shows that hormonal contraceptives alter the scent of lemurs, making them less attractive to males and disrupting clues about their relationship to other group members and other genetic qualities.  The study could have worrying implications for humans who use hormonal contraceptives and may explain why some captive primates – among whom the administration of such contraceptives is becoming more frequent – show unusual patterns of aggression.

Researchers at Duke University studied the effect of the hormonal contraceptive MPA (better known by its Pfizer brand name of Depo-Provera) on captive ring-tailed lemurs.  MPA is commonly used as a contraceptive by humans and is increasingly used with captive primates for conservation and control purposes.  While it has long been known that hormones play a significant role in regulating the smells given off by animals, nobody has ever investigated the effect that hormonal contraceptives have on the odours emitted.

Previous research has shown that body odour can strongly influence the detection of a potential mate’s fertility, quality and genetic compatibility in humans as well as other animals.  The new research is therefore an important step in investigating a hitherto-unrecognised potential side effect of contraceptives such as MPA.  The scientists found that the contraceptive “radically alters” lemurs’ expression of identity, fertility and attractiveness as expressed through their smell.  Male lemurs appeared to be able to readily detect these changes, as the researchers found that the females given contraception tended to be selected as mates less frequently.

Clues about familial relationships were also disrupted by the contraception – Professor Christine Drea, who worked on the study, said: “There’s something very different about these gals.  If animals are figuring out who their kin are by scent, she no longer smells like her brother.”

The next step is clearly to determine whether humans experience the same effects of these contraceptives as lemurs.  Given that human smells have already been shown to contain clues about hormonal status and potential compatibility, the potential significance of the new research is obvious.  As Professor Drea points out, “One has to wonder if human mate choice might be affected in some of the ways it has been in these primates”.