Dinosaur Comics is frequently informative. Today’s comic provides an interesting lesson in flatworm reproduction:
You can watch a video of flatworms penis-fencing here. For me, the take-home lesson from this is that specialization and clear social roles reduce transaction costs. There are also other ways to reduce transaction costs. Some flatworms, for example, reciprocally reproduce: each partner inseminates the other, so both simultaneously becomes a mother and a father.
My first reaction to gender specialization is that it’s efficient but thoroughly unfair. Everyone avoids the cost of penis-fencing, but only through half the population losing all the time. It’s as if a proxy for the penis battle is fought through the pure chance of genetics at conception, with everyone accepting their place thereafter. This unfairness, at least from a pure biological point of view, is illusory.
The skilled penis fencer can expect to have more offspring than the unskilled, since it can impregnate many others without having to bare the costs of pregnancy itself. The situation is different with gender specialization. Since every child has both a mother and a father, the individual who always gets pregnant doesn’t lose in the same way the loser of the penis-fencing contest does. Males always win the penis fencing contest, because females are unarmed. But since exactly one male and one female are required to produce a child, the expected number of offspring does not depend on gender.
Of course, females do need to devote more resources to the production of any particular offspring. This is counteracted by the fact that males are more likely to miss out on reproduction altogether (especially in harem species). Simple economic theory suggests that males will be willing to expend considerable resources in the attempt to reproduce: males are reproductive rent-seekers. This rent-seeking is costly and inefficient. It is also largely zero-sum. Reproductive success in the long run could be maximised if all males of a species could agree not to engage in sexual rent-seeking. Who’s with me?