Michael Stoddart on Sex Smells and Human Evolution

Michael Stoddart, retired Zoology professor at the University of Tasmania, published the book Adam’s Nose, and the Making of Humankind earlier this year. He wrote a very short version for the Guardian this week entitled, “Smell, evolution and the sex brain: why we’re monogamous and use perfume“, which succinctly presents his thesis: that an evolutionary adaptation in the human smell system 16 million years ago changed human mating practices and allowed more social cooperation.

For “why we’re monogamous”, one might substitute “why we’re more monogamy-prone than most mammals”. Let’s not give ourselves too much credit. That’s my only quibble.


First, Stoddart lays out how most mammals do things.

In mammals, the so-called “secondary olfactory system” is responsible for stimulating the sex brain.

This system works not through the nose, but through a structure called the vomeronasal organ (VNO), a chemical sensory organ lying above the hard palate in the roof of the mouth.

Stallions and rams can be seen drawing back their lips to open the VNO when in the vicinity of a female on heat. Female mammals produce special smells to let potential mates know they’re ovulating.

In addition to smell advertisements, many of our primate relatives provide visual signals of ovulation in which the ano-genital region becomes inflated into brightly coloured fleshy cushions.

How and when did humans veer so far from standard mammal operating procedure?

Evolutionary pressure to maintain monogamy and the family bond increased, and it first resulted in the disappearance of visual advertisements of ovulation. Smells advertising ovulation disappeared when a gene mutation that interrupts the flow of information from the VNO to the sex brain – nicknamed “Adam” by its discoverers – appeared about 16m years ago. This was at about the time our early ancestors were starting to live communally on the open plains.

And where does perfume enter into it?

“Adam” didn’t affect the brain’s neural pathways that were originally used to trigger sex. We can stimulate them with sensual perfumes made from – among other things – the sexual signals of musk deer, beavers and civets.

When you put it that way, perfume and cologne sound kinda gross.

Fascinating stuff. If you prefer getting your popular science in podcast form, download a 48-minute interview with Michael Stoddart from Australian ABC.