Since when do people kiss?
The kiss can look back on a long evolutionary history. It probably already existed among the Neanderthals.
Kissing as an intimate gesture probably became established in evolution a long time ago. According to a study published in the journal «Evolution and Human Behaviour», human ancestors were already kissing around 20 million years ago. According to this, Neanderthals probably also exchanged such caresses.
The kiss is an evolutionary biology puzzle. Kissing behaviour can be observed in many animals, but does not appear to offer any direct selective advantage. In fact, it even harbours risks such as the transmission of diseases. Several scientists, such as the Austrian behavioural scientist Irenäus Eibl-Eibesfeld (1928-2018), speculated that the sexual-romantic kiss could have evolved from the feeding of pre-chewed food that mothers pass on to their babies from mouth to mouth. On the other hand, kissing does not occur in all human cultures.
In their search for the evolutionary origin of this peculiar behaviour, the evolutionary biologist Matilda Brindle from the University of Oxford and her colleagues first defined what a kiss actually is. According to them, it is a non-aggressive mouth-to-mouth contact without food transfer.
The team then evaluated studies that describe this type of behaviour in primates. Using statistical methods, they then created a family tree of kissing behaviour.
The Neanderthals did it too
The last common ancestor of humans and their relatives is estimated to have known kissing as a sexual characteristic between 21.5 and 16.9 million years ago. Neanderthals are also likely to have kissed. The statistical model gives a probability of 84 per cent for this. This is supported by the fact that traces of genetic material from microbes such as Methanobrevibacter oralis, which are typical of human oral flora, have been detected in Neanderthal fossils.
The significance of the study is limited, however, as the authors themselves emphasise. They were only able to roughly categorise in monkeys whether kissing «is present» or «was not observed». However, the lack of evidence does not mean that this behaviour never occurs. And the frequency with which it is practised in the different species was also not included in the analysis. Possible selective advantages of kissing were not analysed. The researchers see their publication as the first approach to reconstructing a biological phenomenon that leaves no fossilised traces. This means that kissing will retain its secrets for the time being.
Spectrum of Science
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Original article on Spektrum.de
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