1 Only you: Human lips are different from those of all other animals because they are everted, meaning that they purse outward.
2 But we are not the only species to engage in kissing-like behaviors. Great apes press their lips together to express excitement, affection, or reconciliation.
3 Scientists are not sure why humans kiss, but some think the answer lies in early feeding experiences. Through nursing and (in some cultures) receiving pre-chewed food from a parent's mouth, infants may learn to associate lip pressure with a loving act.
