Wednesday, 28 November 2012

Kin selection's domain

The Price equation pretty clearly implied that any sort of inheritance is likely to be subject to forces associated with kin selection. However, the message seems to have sunk in slowly. Kin selection was applied to DNA-mediated inheritance, but cultural inheritance was almost completely ignored by theorists.

A widespread lack of understanding of the evolutionary significance of cultural transmission could have been responsible. Also, when cultural kin selection was studied, it was often called something else. Tag-based cooperation was one popular term. Tag-based cooperation covers both genetic and cultural kin selection.

Mimicry is another area where kin selection applies. Sysyems involving mimicry may be broadly classified into organic-mimicing-organic, cultural-mimicing-cultural and cultural-mimicing-organic.

Based on the idea of similarity selection, another source of similarity in nature involves convergent evolution. Some convergent evolution involves copying from another organism - for example the parasites of swans may convergently evolve to be white. Other types involves copying from the environment, or from the laws of physics. Kin selection based on convergent evolution may happen - but it isn't easy to think of good examples. Convergent evolution is a research area for kin selection theorists.

Lastly, there's universal Darwinism to consider. Kin selection probably applies to abiotic systems as well - but again, it is not easy to think of good examples. The best cases of high-fidelity copying there are probably crystal growth and positional inheritance. Abiotic systems represent another research area.

Tuesday, 27 November 2012

Kin selection and mimicry

Mimicry is not normally regarded as being a form of kin selection. However, it is pretty clear that mimics engage in copying of traits - and if the individual which is being copied changes its traits, the mimic tracks the changes. Thus, mimicry can be classified as a form of copying (or inheritance) that crosses species boundaries.

There are concrete examples in nature of cooperation based on mimicry. The classic example is the cuckoo. Cuckoos mimic the eggs of their hosts - often in considerable detail - in order to elicit cooperative feeding behaviour from them. The mimicry is necessary - since the hosts employ kin recognition based on egg shell traits in order to identify their own offspring. Modifications in the host eggs are eventually copied by the cuckoo lineage - proving that genuine copying is going on.

Kin selection is clearly involved in the mimicry of the cuckoo - but most would characterize it as a case of kin selection gone wrong - since the benefits go to non-kin.

An alternative analysis looks at relatedness between the copied egg shell traits. These have managed to extend themselves beyond the host species, by copying themselves into another species - thereby gaining access to the resources of a different niche. Since many host eggs perish for each cuckoo egg, this might not seem like a good deal for the trait - but such spreading between species often turns out to be a smart move in the long run.

Of course, mimicry also happens in human culture. For example, viral videos spawn parodies which are a form of cultural mimicry. There's also mimicry between culture and organic organisms - for example, Kermit the frog mimics an organic frog.

Mimicry shows that kin selection can still apply between what seem to be non-relatives, provided they share an inherited trait. Cooperation can result because the traits themselves are kin - in the sense that one of them is copied from the other one.