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Installation 44: The Nose and Our Evolutionary Impulse: Sex, part two

As a clinical mental health therapist I spend a lot of time trying deeply not to pathologize normal behavior in one breath, and trying to research biological and science-based clues to our social and emotional functioning to make a case, make sense of or dissolve a diagnosis. I work with adolescents often, and this is a magical, curious and intense time for exploring sexuality. Gender affirming care feels vital right now, and gender exploration has never been more exciting though at times translucent and hard to name.

I explore often and widely to share nuggets with my clients who are especially curious about the how, what, where and when. I also continuously build a sturdy research pile to share with any skeptical caregivers. I began learning about the research of Daniel Pfau, PhD several years ago during COVID, when I listened to hours of talks on neuroscience, behavior, applied psychology, neuroendocrinology and gender. An excellent talk on the science of gender here if you are curious - Allie Ward is a playful, serious science journalist, I highly recommend her interview with him and her podcast generally. In sum, the variety of genders that are blossoming have very cool, scientific underpinnings that are related to our biology, and our physiological and social evolution.

During the time of this recorded talk Dr. Pfau published a paper about the “De-Scent of Sexuality” where he and his colleagues proposed that the absence of a protein, the transient receptor potential cation channel 2 (TRPC2), that is used to signal pheromones causes same-sex sexual behavior (SSSB). The loss of the protein is found in catarrhine species and not observed in the strepsirrhine, and only a bit in the platyrrhine species. Catarrhine species are “Old World Monkeys” where humans are included in the mix and is characterized by their nostrils being close together and nose facing downward (from Ancient Greek katà-, "down", and rhin-, "nose”). Platyrrhine have noses faces sideways and strepsirrhines have wet snouts.

The protein missing TRPC2 in our species the catarrhine, is found in the vomeronasal organ. This is also known as Jocob’s Organ and is a fascinating accessory organ to the olfactory system that is NOT functioning in humans. We have vestigial remnants of the organ, though sadly no functioning vomeronasal organ. Other species use this organ to sort sexual pheromones and smell things through mud and other obstacles. I am simplifying greatly for sake of brevity, but over time we humans lost its function.

Dr. Pfau and his lab knocked out the TRPC2 in mice to watch their behavior. Turns out when they took it out, the males were less aggressive to each other, and momma mice did not respond as wildly to protect their babies. They, both male and female, also started exhibiting SSSB were before they had not. So this little protein and a new lacking ability to organize the sexual pheromones allowed for a more relaxed social response in the mice.

“Perhaps the loss of a protein that previously enforced opposite-sex behavior by organizing or activating brain responses to male or female pheromones made SSSB more likely in a primate ancestral species.” (Pfau et al)

So one could extrapolate to consider that as humans, if we allowed ourselves to become less aggressive in order to survive and socialize more, losing the scent protein was a social adaption. So any SSSB it turns out is highly adaptive and natural. Voila.

Also further food for thought that in fact it may not be the pheromones that we are smelling that are a “turn on” especially given the fact that we humans have a pheromone signal missing. It may be something completely different. It makes sense that visuals are so powerful in sexual attraction given our dulled sense of pheromone detection and organization. Smell will forever be a part of the yum yuck cycle of seduction, so long live fragrance signaling whether natural or curated.

Including these thoughts in the Odorbet to document further that our noses are tied profoundly to our sexuality. I wrote years ago about this here on the Odorbet and look forward to uncovering more. Sidenote - scientific papers are impossible to access in the USA. I had to ping my relative in graduate school (thank you Thea!) to get this full paper. A plea to the academic systems of the world - stop gate keeping information please. If you would like a copy of the paper please contact me.

Research Cited:

Pfau, D., Jordan, C.L. & Breedlove, S.M. The De-Scent of Sexuality: Did Loss of a Pheromone Signaling Protein Permit the Evolution of Same-Sex Sexual Behavior in Primates?. Arch Sex Behav 50, 2267–2276 (2021).

Nose Terms Used:

The following zoological categories are relating to primates:

Catarrhine - species with nostrils close together and directed downward (e.g., Old World Monkeys, humans)

Happlorhines - species with dry noses (e.g., apes and humans)

Strepsirrhines - species with wet noses (e.g., lemurs and bush babies)

Platyrrhines - species with noses faces sideways (e.g., new world monkeys)

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