Podcast Summary: Short Wave – “Why do we kiss? It's an evolutionary conundrum”

Date: February 13, 2026
Host: Emily Kwong
Guest: Dr. Matilda Brindle, evolutionary biologist, University of Oxford

Main Theme

This episode delves into the evolutionary mystery of kissing—why do humans (and other animals) kiss, what purposes might it serve in terms of evolution, and how do cultural and biological influences intertwine in the act of kissing? With humor and accessible science, host Emily Kwong and guest Dr. Matilda Brindle explore the distinctions between platonic and sexual kissing, investigate which animals practice it, and examine whether kissing is innate or learned.

Key Discussion Points & Insights

1. The Universality & Mystery of Kissing

• Cultural Phenomenon: Kissing is pervasive in Western culture—central in movies, idioms, and rituals (e.g., Sleeping Beauty, “kiss of life”).

• Not Actually Universal: Not all human cultures have a tradition of kissing.

  • [01:25] “[Kissing] just does seem like this huge, huge cultural phenomenon... movies end with a kiss...all of these really important kind of cultural things.” — Dr. Matilda Brindle

• Gross but Widespread:

  • [01:45] “It's this amazing, weird thing we do that looks totally pointless and kind of a bit gross and, you know, counterintuitive. We're probably sharing loads of germs.” — Brindle
  • [01:57] “80 million bacteria are estimated to be transferred on average in a 10-second kiss.” — Kwong

2. Why Is Kissing an Evolutionary Conundrum?

• Kissing is risky: exchanging bacteria, exposing oneself to disease, and making oneself physically vulnerable.
  • [04:18] “Kissing seems like a very unhygienic and vulnerable thing to do...” — Brindle
  • [04:46] “Putting your mouth next to someone's face is potentially a dangerous thing to do if you're not sure they like you. Particularly, you know, if you're a polar bear, that’s some big teeth...” — Brindle

Notable Moment

• Polar Bear Kissing!
  • [05:13] “They kiss. Yeah. And we're not quite sure why...there is a lot of froth and foam going on...” — Brindle
  • [05:31] “I’m watching this video of polar bears from the Budapest Zoo...their mouths are foaming. It's like a car wash in between their mouths.” — Kwong

3. Defining Kissing in Scientific Terms

• [05:50] “We define kissing as a non agonistic interaction...intraspecific...oral contact with some movement of the lips or mouth parts and no food transfer.” — Brindle
• This broad definition allows comparison between humans, polar bears, ants, and other species.

Memorable Exchange

• [06:14] “That’s possibly the least romantic definition of kissing imaginable.” — Kwong

4. Kissing in Other Animals

• Animals That "Kiss":
  • Polar bears (“frothy nightmare”)
  • Ants
  • Albatrosses
  • Prairie dogs
    • [07:21] “A tiny bit of oxytocin was released as I looked at this photo of these two prairie dogs. One of them is caressing the other's face.” — Kwong

5. The Evolutionary Roots: Primates & Ancient Ancestors

• Kissing likely present in the ancestor of all apes 21 million years ago.

  • Example: Pliobates cataloniae (lived ~11.5 million years ago, found in Spain), likely similar to modern gibbons but slower.
    • [07:47] “[Kissing] was likely present in the ancestor of all apes who lived 21 million years ago.” — Kwong, referencing Brindle’s research

• Two Types of Primate Kissing:

  • Platonic: e.g., chimps reconciling after conflict
  • Sexual: e.g., bonobos, “using a lot of tongue. It’s described as very sensual.” — Brindle [08:46]

Distinction

• [09:04] Sexual vs. Platonic distinguished by context (are sexual behaviors present? Is it parent-offspring?).

6. Why Did (Sexual) Kissing Evolve in Primates?

• Two Main Hypotheses:
  1. Mate Assessment ([10:19]):
     • Smelling/tasting partner provides info about health and genetic compatibility via olfactory clues.
     • “There’s some evidence to suggest we can use olfactory clues to tell whether someone's major histocompatibility complex is similar to our own...It makes sense to mate with individuals that have more dissimilar...complexes, because that might improve our immune function.” — Brindle [11:21]
  2. Pre-copulatory Arousal ([12:02]):
     • Kissing helps ensure comfortable, successful copulation, increasing chances of fertilization.
     • “It just might be tipping the scales in favor of being fertilized by that individual.” — Brindle

7. Evolution of Platonic Kissing

• Bonds parent-offspring, fosters social ties, increases oxytocin.
• Sharing the microbiome — especially beneficial for babies, prepping their immune systems via maternal kisses.
• Also helps mitigate social tension.
  • [12:17] “There’s a release of oxytocin associated with this, which helps us to bond...and then...sharing the microbiome...increasing that immunity.” — Brindle

8. Is Kissing Learned or Innate?

• Highly variable by species and culture (e.g., chimpanzee vs. bonobo, cheek kissing varies by region).
• Cultural learning plays a big role.
  • [14:01] “We do teach each other to kiss. We kind of see other people do it and, you know, nobody’s first kiss is good, is it?...This is something you learn...There’s an interplay between [culture and evolution].” — Brindle

9. Future Directions in Research

• Need for more data on animal sexual behaviors, especially non-reproductive ones; much yet to discover.
  • [14:50] “We need to take these behaviors seriously...maybe this is societally a little bit uncomfortable to look at, but there's so much to be discovered...” — Brindle

Notable Quotes & Memorable Moments

• On evolutionary awkwardness:
  • [04:18] “Kissing seems like a very unhygienic and vulnerable thing to do...” — Brindle
• On the spectrum of animal kisses:
  • [07:01] “The birds, yeah. And obviously, again, they don’t have lips. I think there’s a David Attenborough clip somewhere on the Internet of this.” — Brindle
• On first kisses:
  • [14:01] “Nobody’s first kiss is good, is it? Or mine certainly wasn’t.” — Brindle

Timestamps for Important Segments

• [01:25] – Kissing as a major cultural phenomenon
• [04:18] – Why kissing is risky from an evolutionary perspective
• [05:50] – Scientific definition of kissing
• [06:58] – Surprising animal “kissers”: ants, albatrosses, prairie dogs
• [07:47] – Ancient evolutionary roots of kissing in primates
• [09:59] – Hypotheses for why sexual kissing evolved
• [12:02] – Platonic kissing and its evolutionary advantages
• [14:01] – Is kissing learned or innate?
• [14:50] – Where future research could go

Tone & Style

The conversation is light, humorous, and personable—balancing scientific rigor with playfulness (“frothy nightmare,” “nobody’s first kiss is good”) to make complex evolutionary questions accessible to all listeners.

This summary captures the episode’s engaging exploration of kissing’s mysteries, providing a roadmap for anyone curious about why we kiss, which animals do it, and the interplay between biology and culture.