Rosa Rubicondior: Refuting Creationism - Kissing Goodbye to Childish Superstitions

Ape ancestors and Neanderthals likely kissed, new analysis finds | University of Oxford

Researchers have shown that kissing emerged early in the human evolutionary lineage, and that Neanderthals, along with other close relatives in our tangled family tree, almost certainly kissed as well.

Kissing is an intriguing behaviour, widely assumed to serve important social functions that outweigh the obvious drawbacks of exchanging microbes and viruses.

The team, led by Dr Matilda Brindle, an evolutionary biologist in Oxford University’s Department of Biology, based their conclusion on the principle that when two species on separate branches of the primate family tree share a behaviour, it was likely present in their common ancestor. This approach indicates that kissing arose among the ancestors of the great apes between 21.5 and 16.9 million years ago. Their findings were published very recently in the journal Evolution and Human Behavior.

Creationists who insist that evolutionary biologists are abandoning the Theory of Evolution—a framework on which this analysis directly relies—may be alarmed to find no evidence of such a retreat. Quite the opposite: the observation that a trait with both costs and benefits will persist when the benefits outweigh the costs neatly explains the evolutionary retention of kissing across several related species.

Hazards of kissing. Viruses commonly spread by kissing

Epstein–Barr virus (EBV) - the cause of glandular fever/mononucleosis (“the kissing disease”).
Herpes simplex virus type 1 (HSV-1) - oral herpes; can spread even without visible sores.
Cytomegalovirus (CMV) - usually mild but can be serious in immunocompromised individuals and during pregnancy.
Human papillomavirus (HPV) - certain strains can spread through saliva and oral contact.
Respiratory viruses - such as influenza, RSV, adenoviruses, rhinoviruses, and others.
SARS-CoV-2 - the virus responsible for COVID-19, readily transmitted by close contact and shared droplets.
Bacteria that can be passed through kissing

Streptococcus mutans - a major contributor to dental caries (tooth decay).
Neisseria meningitidis - can cause meningitis and septicaemia; often spreads through close contact.
Streptococcus pyogenes - associated with strep throat and other infections.
Helicobacter pylori - linked with stomach ulcers; thought to spread through saliva in some cases.
Periodontal bacteria - including Porphyromonas gingivalis, which contributes to gum disease.
Fungi and other organisms

Candida species - can cause oral thrush, particularly in those with weakened immune systems.

Oxford University has also summarised the team’s research in a recent news release.

It is also explained in an article in The Conversation by Dr. Matilda Brindle. Her article is reprinted here under a Creative Commons licence, reformatted for stylistic consistency.

Published: November 19, 2025 6.08am GMT

When did kissing evolve and did humans and Neanderthals get off with each other? New research

Moncar0/Shutterstock

Matilda Brindle, University of Oxford

If I asked you to imagine your dream snog, chances are it wouldn’t be with a Neanderthal; burly and hirsute as they may be. However, my team’s new research suggests that these squat beefcakes might have been right up your ancestors’ street.

In our new paper, colleagues and I investigated kissing in monkeys and apes, including modern humans and Neanderthals, to reconstruct its evolutionary history for the first time.

Before we could do this, we needed to construct a definition of kissing that was applicable across a wide variety of animals. This sounds simple, but lots of behaviour looks like kissing at first glance.

Many primates pre-chew food for their offspring and feed this to them orally (a behaviour known as premastication). Ants also exchange fluid and food mouth-to-mouth in a process known as trophallaxis. Sometimes they do this mouth-to-anus too, but that is harder to mistake for a kiss. Tropical French grunt fish can also be seen passionately locking lips. However, this behaviour is no French kiss. It is part of a dominance display known as “kiss-fighting”.

We excluded kissing-like behaviour from our definition. We also excluded interactions that might be accidental or occur between members of different species, such as when dogs lick their owners’ mouths (or the time a capuchin monkey tried to snog me, but that’s a different story).

Taking all this into account, we define kissing as non-aggressive, directed, mouth-to-mouth contact between members of the same species, that doesn’t involve food transfer. By this definition, all sorts of animals kiss, from polar bears enjoying spirited rounds of tonsil-tennis, to prairie dogs softly canoodling.
We used this definition to trawl published scientific papers, searching for observations of kissing in the group of monkeys and apes that evolved in Africa, Asia and Europe. It turns out that a handful of monkeys, and most apes, have been observed to kiss, with the exception of Eastern gorillas and the small apes (gibbons and siamangs).

The type of kiss can vary, both within and between species. Kissing between bonobos tends to be an exclusively sensual affair with “prolonged tongue-tongue interaction”. Other apes have a spicy side too, sometimes kissing as foreplay, or during sex.

Kissing also occurs in affectionate, platonic contexts across most apes, such as when mothers kiss their infants, or during greetings and reconciliation.

We combined this data with information on the evolutionary relationships between different species, in what is known as a phylogenetic comparative analysis. This technique allowed us to model the evolutionary history of kissing, and explore whether it was likely to have been present in the ancestors of different groups of species.
Our results paint early apes in an amorous light, showing that the ancestors of large apes were kissing each other as far back as 21.5 – 16.9 million years ago. Clearly, they were onto a good thing because they’ve been at it ever since, apart from Eastern gorillas, who just don’t seem to be into it.

Our reconstructions also shed light on the proclivities of Neanderthals who, it turns out, were also likely to be partial to a good smooch. Previous research shows that modern humans and Neanderthals shared an oral microbe long after the two species diverged into separate lineages. For this to happen, the microbes had to have been transferred between the two species. In other words, they were swapping saliva.

There could, of course, be an innocent explanation for this. Perhaps the two species were simply sharing food with one another over a friendly campfire. On the other hand, when you consider that most people of non-African descent have some Neanderthal ancestry, alongside our finding that kissing was present in Neanderthals, a saucier picture emerges.

So, did humans and Neanderthals get off with each other? Unfortunately, kissing doesn’t preserve in the fossil record, so we’ll never be able to say for sure, but the evidence certainly points in that direction. One thing I can say for certain is that I’ll never look at a Neanderthal the same way again.
Matilda Brindle, Postdoctoral researcher, University of Oxford

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Published by The Conversation.
Open access. (CC BY 4.0)

Abstract
Kissing can be observed across the animal kingdom. This presents an evolutionary puzzle, since the fitness benefits of kissing are unclear. We use a non-anthropocentric approach to define kissing as a non-agonistic interaction involving directed, intraspecific, oral-oral contact with some movement of the lips/mouthparts and no food transfer. Using this definition we collate basic observational data across the Afro-Eurasian primates and employ Bayesian phylogenetic methods to reconstruct the evolutionary history of kissing. We find that kissing occurs in most extant large apes, and likely also occurred in Neanderthals (Homo neanderthalensis), first evolving in the ancestor to this group ∼21.5–16.9 mya. Additionally, we highlight various life history variables that correlate reasonably, but not perfectly, with kissing across the apes (multi-male mating systems, non-folivorous diets, and premastication). With a major caveat about the quantity of available data at present, we hope that our results provide a useful starting point for further research into the adaptive function of kissing that highlights hypothesis generation and testing within a phylogenetic framework.

Fig. 1. Top panel: kissing across the animal kingdom (clockwise): Rhesus macaques (Macaca mulatta; credit: Paula Bronstein, Getty Images); Galapagos albatross (Phoebastria irrorata; credit: Vladimir Jurek, Shutterstock); Polar bears (Ursus maritimus; credit: Smiler99, Shutterstock); Wolves (Canis lupus, credit: Soren Wolf, Flickr); Prairie dogs (Cynomys ludovicianus, credit: Brocken Inaglory, Wikimedia Commons). Bottom panel: non-kissing mouth-to-mouth behaviours (left to right): premastication in orangutans (Pongo sp., credit: Sunsetman, Shutterstock); trophallaxis in ants (Camponotus compressus, credit: Rakeshkdogra, Wikimedia Commons); and kiss-fighting in French grunts (Haemulon flavolineatum, credit: Luiz A. Rocha, Shutterstock).

Brindle, Matilda; Talbot, Catherine F.; West, Stuart
A comparative approach to the evolution of kissing
Evolution and Human Behavior (2025) 106788 DOI: 10.1016/j.evolhumbehav.2025.106788

Copyright: © 2024 The authors.
Published by Elsevier Inc. Open access.
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)

What this study illustrates so clearly is how comfortably behaviours such as kissing fit within an evolutionary framework. When a trait appears in several related species, the simplest explanation is that it was present in a shared ancestor and was passed down as those lineages diverged. The precise functions may shift over time, but the underlying behaviour persists because, overall, it continues to offer advantages—strengthening social bonds, reinforcing pair bonds, or facilitating mate assessment—despite the obvious risks involved. This is exactly what the Theory of Evolution predicts: traits are retained when their net benefit favours survival or reproductive success.

Kissing represents a textbook example of this dynamic. It is not perfect, risk-free, or optimally engineered; it is a compromise shaped by natural selection, never starting from scratch but constantly modifying what already exists. The microbes and viruses that can be exchanged through intimate contact are part of that evolutionary landscape too, because pathogens themselves evolve and exploit available opportunities. This interplay of benefit and risk is precisely what we expect when a behaviour is the product of biological history rather than deliberate design.

By contrast, creationism provides no meaningful account of why closely related species should share something as specific as kissing, nor why a supposedly perfect designer would endow creatures with a behaviour that carries clear, sometimes serious, health risks. The idea that such traits were intentionally created in this flawed state strains credulity. Evolution, on the other hand, offers a coherent, evidence-based explanation that not only accommodates such imperfections but positively predicts them.

Far from signalling any abandonment of evolutionary thinking, studies like this demonstrate the continuing power of the Theory of Evolution to illuminate even the intimate details of human and primate behaviour. As ever, the natural world makes far more sense when we follow the evidence rather than cling to conclusory assertions that explain nothing.

Advertisement

Amazon