The Bruce Effect
The Bruce Effect, also known as pregnancy block, refers to the predisposition of a female rodent to terminate its pregnancy in response to the scent of a foreign male rodent. This was first described by Hilda Bruce, a British zoologist, in 1959. Specifically, it was observed that miscarriages among pregnant mice significantly increased when housed with unfamiliar male mice. The termination of pregnancy was also likely to be followed by copulation. The Bruce Effect has an evolutionary benefit since female rodents can reserve their reproductive resources for the best male. Also, since male mice tend to kill unrelated pups, the pregnancy block prevents the wastage of offsprings.