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People do it, monkeys do it, including arctic bears participate in it. And now, scientists have traced the evolutionary beginnings of mouth-to-mouth contact.

Their study suggests that the oral-oral kiss evolved over 21 million years ago, and was a behavior that the shared predecessor of humans and additional great apes probably indulged in.

The same study concluded that ancient humans could have kissed as well – and that humans and our ancient relatives might have exchanged kisses one another.

Through discovering evidence of additional creatures engaging in mouth contact, scientists could build an "evolutionary lineage" to determine when it was probably to have evolved.

To make certain that they were examining the identical behaviour across different animal types, the scientists had to give a very precise – quite clinical – definition to a "smooch".

In their study, published in a scientific journal, they described oral contact as non-hostile, focused mouth-to-mouth interaction "with some movement of lips or mouthparts and without nourishment exchange".

"People, chimpanzees, and bonobos all engage in kissing," explained principal investigator Dr Matilda Brindle. From that, she determined, "it's likely that their closest shared predecessor practiced kissing."

"Researchers believe kissing probably developed approximately 21.5 thousand-thousand years ago in the large apes."

During this research, scientists found behaviour that fit their scientific definition of kissing in wolves, prairie dogs, polar bears (very sloppy – much tongue), and including seabirds.

They concentrated on primates – and large primates in particular – in an effort to construct an evolutionary understanding of the origin of the human kiss.

This study additionally found that Neanderthals – our nearest ancient human ancestors that became extinct approximately forty thousand years before present – too engaged in kissing.

Earlier study on ancient human genetic material also revealed that modern humans and Neanderthals had in common an mouth bacteria – a kind of microorganism found in our mouth fluid.

"That means that they must have been exchanging mouth fluid for many hundreds of thousands of years after the both groups split," commented the lead researcher.

Although this study identified when kissing developed it was could not answer the question of why.

There are numerous a number of hypotheses – that it arose from cleaning behavior in our primate ancestors or that it might provide an intimate way to evaluate the health and even the suitability of a partner.

The lead researcher expects that this will open a door to solving that question.

"It's crucial for humanity to recognize that this is a behavior we share with our non-human relatives," she commented.

"We should be investigating this behavior, rather than discarding it as frivolous because it has affectionate associations in humans."