Evolutionary stability of courtship

I’m currently reading The Selfish Gene by Richard Dawkins. Dawkins revels in analysing various scenarios through the lens of Evolutionarily Stable States (ESS) wherein each organism has a pre-determined strategy on how to act in the world. Using simulations, one could determine how such strategies would help or hurt the organism and eventually give us an optimum mix of different strategies that would be “evolutionarily stable”, i.e give favourable outcomes on average to most organisms. In an earlier post, I spoke about how it is sometimes useful for strong pacifists and weaker aggressors. In this post, I’ll detail courtship through the lens of ESS.

Dawkins defines males as members of a species which produce smaller reproductive cells, i.e sperms. Similarly, females are defined as members of the species which produce bigger reproductive cells, i.e eggs. Sperm cells are near-unlimited and optimized to find and mate with as many eggs as possible. Eggs, on the other hand, are finite in number and rich in resources to provide for the offspring. This usually means that males are dispensable and the females tend to be more valuable for the survival of species as a smaller number of male specimens can potentially provide the sperm cells required to copulate with a larger number of female specimens. In certain species of elephant seals, 4% of males father near 80% of the offsprings.

As per the selfish gene principle, each individual is interested in propagating its own genes further. In order to do this, males and females must copulate. This mating exercise is accompanied by the following objectives and strategies:

Objectives of the sexes:

1. The males of the species have a near-unlimited supply of sperm cells. The ideal outcome for the males involves using these numerous sperm cells to produce multiple offsprings
2. The females of the species have a limited supply of eggs. The females also take a considerable time in bearing the children until childbirth. This generally means females need to ensure their choice of partners can help share the burden of bearing and rearing children

Strategies employed by males:

1. Faithful — In this strategy, males exhibit monogamous traits. “Faithful” specimens follow successful courtship with sticking with their partners to raise their children
2. Philanderer — In this strategy, males primarily look to copulate with as many females as possible. After successful copulation, the “philanderer” moves on to his next conquest

Strategies employed by females:

1. Coy — In this strategy, the females take their time in picking their partners. This involves a cost of having to wait but has the benefit of weeding out philanderers who may not be prepared to stick it out with one partner. This strategy ensures the “coy” females are more likely to end up with “faithful” partners
2. Fast — In this strategy, the females of the species are “fast” in choosing their partners. This reduces the cost of pruning but involves the risk of copulation through a philandering partner and being left to bear and rear children alone

In a society with only faithful males, fast females have the advantage of being able to reduce the cost of prolonged courtship.

In a society with only fast females, philanderers have the advantage of being able to copulate numerous females and leaving them to bear and rear their children thus propagating their genes.

In a society with philanderers and faithful males, coy females can successfully improve the odds of finding a faithful male to share the responsibilities of raising the children.

In a society with coy females, faithful males have better odds of successfully finding a partner to copulate with thus propagating their own genes.

An evolutionarily successful society would contain a healthy mix of faithful, philanderer, fast and coy. In any idealistic combination, there is an incentive to “cheat”. With only faithful males and fast females, a philandering male immediately gains an advantage. In a society with faithful males and coy females, a fast female gains the advantage. Evolutionarily, the most practical situation involves societies where all strategies exist in stable proportions.