Five Behaviors Explained by Evolutionary Psychology

Kissing

Kissing is believed to have originated as a means of testing the opposite sexes immune system. The mouth is one of the most bacterially-abundant places on the body and thus exchanging saliva will introduce the prospective mate with lots of different types of pathogens. The logic goes that if the mate has no negative response to this experience then they will be a suitable mate due to the fact that they have a strong immune system which would be a preferable characteristic for offspring.

An additional “bonus” of kissing is that it allows prospective mates to get close enough to each other to smell each other. When humans were more primitive mating would have relied heavily on the exchange of scents and hormones. Even in modern times the smell of the opposite sex has a higher role to play than most people would realise.

Kissing is not entirely in our genes however; as it is widely believed by scientists to be largely due to our upbringing that we find kissing attractive. From a very young age we will have probably seen and experienced our parents kissing to show love, care and gratitude. Coupled with the way in which kissing and such affection is portrayed in our culture we are bound to grow up to learn kissing is a good behaviour.

Feeling sick when someone else has vomited

In the times before society had fully developed humanity was believed to be an isolated group of hunter-gathers; essentially surviving on whatever it was that we could find. This may have at times resulted in some fairly dubious meal selections for the tribe.

Should someone else in the tribe vomit it is likely that they will either be ill, or they will have eaten something which has upset their stomach. This means it is likely that other members of the tribe will have eaten the same food, and thus it would be beneficial for the other members of the tribe to regurgitate their food too to avoid being poisoned.

Admittedly the smell of vomit is also highly unpleasant due to its highly acidic and half-digested nature, however that is not to say that via evolution we have not learned to find this smell unpleasant, rather than neutral or even pleasant.