I identify as ace and like to interpret Vulcans as asexual outside of pon farr. When I’m not writing fanfic, I’m a biologist, and so for the Trek Tribute Zine I went into how that - and the rest of their unique mating system (as it appears in The Original Series) - could possibly evolve. Here’s an sneak peak, and I encourage you to check out the rest of the essay and all of the other awesome fanworks in the Trek Tribute Zine!
“We are driven by forces we cannot control to return home and take a wife. Or die.” – Spock (TOS: “Amok Time”)
Every seven years, all Vulcans are compelled to return to their native planet to engage in the ancient ritual of pon farr or die trying (TOS: “Amok Time”; “The Cloud Minders”). Among fans - and some writers of the series itself, if the odd Tumblr post is to be believed - the most contested feature of this unusual mating system is the suggestion that they only mate once every seven years. However, as a biologist, far more remarkable is the fact that any Vulcan who fails to mate dies. From an evolutionary perspective, it’s astounding that such a system could possibly evolve, but there are some possibilities.
First, the most pressing question; why only every seven years? Obviously, there are narrative reasons a writer may want to change this. Even The Original Series, which introduced the Vulcan mating system, seemed conflicted about it (TOS: “The Cloud Minders”). However, as a biologist, that Vulcans only mate once every seven years is perhaps the most normal thing about their reproduction. Humans are one of relatively few species on Earth that reproduce year round. Most species only mate during a particular time of year when there are enough resources available not only for survival, but also for the production and care of offspring (Wingfield & Kenagy, 1991). It makes sense that Vulcans, which live on a desert planet, would have more constraints on when they can reproduce.
Mating every seven years may sound strange, but there are species that reproduce on multiple year cycles; thirteen- and seventeen-year cicadas (Williams, 1995) are probably the most well known. Alternatively, it could be that “the seven-year-cycle” (TOS: “The Cloud Minders”) is measured in Earth years, and is actually one year on Vulcan, or is some equivalent ecologically relevant unit. Being entirely celibate outside of the mating season is also fairly typical. For example, birds that reproduce only once a year often have testes that regress for the rest of the year, making it physically impossible for them to mate - not to mention the hormonal changes that make them no longer have any desire to (Wingfield & Kenagy, 1991). This makes evolutionary sense because if you’re putting a lot of energy into a big reproductive bout, it would be a waste to expend some of that energy on other times of the year when offspring are less likely to survive.
Williams, K. S., & Simon, C. (1995). The ecology, behavior, and evolution of periodical cicadas. Annual Review of Entomology, 40(1), 269-295.
Wingfield, J. C., & Kenagy, G. J. (1991). Natural regulation of reproductive cycles. In Vertebrate endocrinology: fundamentals and biomedical implications, 4(Part B), 181-241.