I found this video on YouTube. The title is self-explanatory but I found it of interest because I’ve been working on a hypothesis on the origins of kissing in humans (see here). That hypothesis was inspired by the clip below.
So just a few observations on a comparison of the Chimpanzee and Bonobo videos. Firstly Bonobos are more distant to us than Chimpanzees. Basically we and Chimpanzees had a common ancestor (concestor) and we diverged about 6 million years ago give or take a few million years. Then a few million years later Bonobos and Chimpanzees diverged. What we and Bonobos have in common is that we have less facial hair than Chimpanzees although obviously in the case of humans it is a lot less (although the hair distribution surrounds the central part of the face in Chimpanzees and Bonobos). The hypothesis states that kissing is an extension of grooming behaviour in other primates and develops from the loss of hair in humans. In the clip of the Chimpanzees, the behaviour is not as convincing as in the Bonobo clip and consists of the Chimpanzees ‘touching’ lips. Perhaps this is associated with a feeling of security as it appears to be a parent and child. The activity is qualitatively different to that of the Bonobos where it has clear characteristics of grooming. This is exemplified by the clip below
Although Bonobos have less facial hair than Chimpanzees, the occurrence of hairless facial skin in both cases presents an opportunity for this transformative grooming behaviour. Nevertheless in this Chimpanzee video at least it does not offer any convincing evidence either way on the grooming hypothesis.
However there is one interesting question it raises. Why do the Chimpanzees keep their lips in contact? The answer I suspect relates to receptors in the skin. Part of the explanation may lie in Mechanoreceptors although the main explanation might be expected from touch light touch sensation. I’ve made some videos on Mechanoreceptors which come in handy in explaining some of the concepts but will eventually get round to the other types of receptors.
In any case if it is common to Chimpanzees and Bonobos then it might mean that the Bonobos behaviour followed a change in receptor structure and function in the hairless skin areas. Although classically associated with hairless areas however, Mechanoreceptors are also found in hairy skin.
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