Fish and the SSH

An intriguing cross-species parallel

In The Genetic Book of the Dead, Richard Dawkins describes a fish that exhibits a male hierarchy remarkably similar to that of the SSH:

One species, Poecilia parae, has a remarkable colour polymorphism, which affects only the males. Polymorphism means that there are different genetically determined colour types coexisting in the population (in this case five colour patterns) and the proportions of the different types remain stable in the population through time. All five male morphs can be found swimming together in South American streams. There’s only one female morph: females look alike.

Since the polymorphism affects only one sex, we can call them five gentes, by analogy with the cuckoos, with the difference that in these fish it’s the males who are separated by gens. The picture shows the five male types plus a female at the bottom. Three of the five male types have two long stripes like tramlines. Between the tramlines there is colour, and I’ll call them reds, yellows, and blues respectively. These three ‘tramliners’ can, for many purposes, be lumped together. The fourth type has vertical stripes. They’re officially named ‘parae’, but confusingly that’s also the name of the whole species. I’ll call them ‘tigers’. The fifth type, ‘immaculata’, is relatively plain grey, like females but smaller, and I’ll call them ‘greys’.

Tigers are the largest. They behave aggressively, chasing rival males away, and copulating with females by force. Greys are the smallest, and they manage to copulate only by occasionally sneaking up on females opportunistically. When they get away with it, it seems to be because otherwise aggressive males mistake them for females, which they do indeed resemble. Greys have the largest testes, presumably capable of producing the most sperm, perhaps to take advantage of their scarce opportunities to use it. Red, yellow, and blue tram-liners are of intermediate size. Rather than rape or sneak, they court females in a civilised manner, displaying their respective coloured flanks.

I am not claiming this scientifically legitimizes the SSH through the usual evo-psych storytelling. That’s quite literally impossible, as those who are familiar with my broader oeuvre know very well.

But since we’re dabbling in evo-babble given the Dawkinsian context, it can’t hurt to throw out the possibility of this being an indicator of a common code on of some sort, especially if it were to be determined that Gamma males are more fertile, on average, than other men.