The Green Beard Mechanism is Bogus

This essay is a lightly reworked version of material from Debunking the Selfish Gene.

Reproductive altruism can’t evolve, because it is less adaptive than reproductive selfishness.

Suppose that a population contains organisms of both types. Some are reproductively altruistic toward other members of the population. The rest are reproductively selfish. The selfish organisms receive a benefit from the altruistic organisms, while the reverse is not true. So, on average, the selfish organisms will be more reproductively successful. The selfish trait will always be positively selected, while the altruistic trait will always be negatively selected. Eventually, the selfish trait will completely replace the altruistic trait. The selfish trait is selectively stable at 100% in the population.

That is why group selection theory is wrong. Group selection does not exist, because the organism is the reproducing unit, and thus organisms are individually selfish reproducers. There are some cases where the reproducing unit is not what we view as the organism, but it is never the species or subspecies.

Many people have tried to find loopholes in this argument. The “green beard mechanism” is an example of a proposed loophole. It is a complex trait with two effects:

• It signals that the organism has the trait.
• It causes altruistic behavior toward other organisms that display the signal.

In the silly example used to illustrate the idea, the signal is a green beard. Organisms with the trait grow a green beard and are nice to other organisms with green beards.

See Green Beard Effect on Wikipedia.

There are three problems with the green-beard mechanism:

• It is too complex to arise by mutation.
• It could be exploited by individuals who display the signal but are not altruistic.
• It is not actually altruistic.

It is very unlikely that such a complex trait could arise by a single mutation. Even if it did, by some miracle, it would not be adaptive initially. In the first generation, there would be no other organisms with the trait, to compensate for the cost of the signal. Even if the founder organism managed to reproduce, there would be only a small number of fellow green-beardists in the next few generations, so the trait would not have a large average benefit, probably not enough to outweigh the cost of the signal. (The beard would require some energy to grow and carry around, and it would also presumably increase the risk of predation.)

If a population with the trait somehow arose, it could be exploited by individuals who display the signal but are not altruistic. If the complex green-beard mechanism could arise by mutation, then surely a simpler version (the signal by itself) could arise by mutation. If it did, it would be positively selected in an environment with green-beardists, because individuals with the parasitic version would benefit from the altruism of others, without paying the cost of being altruistic. The purely selfish version would eventually replace the altruistic version.

Finally, the proposed trait is not actually altruistic. It has an altruistic component: the behavior. But it also has a selfish component: the signal. Whether the trait as a whole is selfish or altruistic depends on the total expected payoff. If the total expected payoff is negative, the trait is altruistic. If the total expected payoff is positive, the trait is selfish.

The green-beard thought experiment assumes that the total expected payoff is positive. The argument that it could evolve depends on this premise. It assumes that individuals benefit from the trait on average, and thus the trait is positively selected. But if individuals benefit from the trait on average, it is selfish, not altruistic.

The green-beard mechanism combines altruism and selfishness in one package. The argument that the trait can evolve depends on the implicit assumption that the trait is selfish as a whole. But the conclusion is that altruism can evolve, because the (selfish) trait can supposedly evolve. This is fallacious.

The green-beard mechanism is bogus. Evolution creates reproductive selfishness, not altruism.