Pregnancy has an odor that reveals unborn baby's sex

“The difference in hormone profiles between pregnant lemurs carrying sons and those carrying daughters is dramatic,” she said in a press release.

“It could be that producing these compounds uses resources that are directed elsewhere when they’re pregnant, especially if it’s more energetically costly for a female to have a male pregnancy than a female pregnancy,” she added.

Presumably, a male’s ability to detect pregnancy — and his possible connection — is particularly important for sexually promiscuous species. Lemurs and most other primates fall into that category. Humans do too.