Kissing and hugging are both ways of showing affection, which refers to when somebody cares a lot about somebody else.
Kissing and hugging both come in many different forms -- for example, sometimes you might hug or kiss a good friend or a relative just to say "hello," "goodbye," or "happy birthday"! Other times, giving a hug or a kiss might be used to cheer up someone you care about when that person is feeling sad. People like husbands and wives also kiss as an expression of their love for each other.
Nobody knows exactly when or why people started using these two things to show how much they cared about someone else, but lots of scientists and researchers think it goes back thousands and thousands of years, and that the desire to hug or kiss might even be a built-in instinct that we're born with!
One possible origin of kissing is that it evolved from the instinct to be close enough to sniff someone, and that eventually people got so close when sniffing that they touched lips! Kissing might also have come from mothers who would chew food and then pass it from their mouth to their infant's mouth, touching the child's lips in the process and creating a symbol of care and affection out of lip-touching!
One of the reasons scientists think hugging and kissing might be an instinct is that lots of animals have their own ways of doing the same thing!
For example, have you ever seen two animals like cats rubbing noses? Or have you ever been licked by a friendly dog?? These actions are the animal's version of giving a kiss!
Other good examples are birds, who will touch their beaks together, and even elephants, who will put their trunks into the mouth of another elephant!!
Do you know of any other animals who have special ways of showing affection??