40. Ooh, What’s That Smell?
Scientists have studied mice that are almost identical genetically, except for changes in their immune system genes. They found that these mice smelled different from each other. Similarly, researchers noticed that in some human cultures where people tend to marry within their own group, there’s less inbreeding than expected.

It turns out that we might be able to smell when someone is a good genetic match for us. So, even though we might not realize it, our noses could be helping us choose partners who are genetically different from us, which is important for healthy offspring.