Kin selection, population bottlenecks, founder effect

Kin selection theory raises the possibility that organisms may use variation between them as clues to relatedness - and direct cooperative behaviour preferentially towards perceived relatives. This effect is sometimes referred to as "kin recognition".

However, this method of identifying relatives depends on the existence of population-scale variation. Population bottlenecks can destroy such variation - and may promote cooperation.

Similarly, the founder effect might also produce local regions with little variation.

These effects have been demonstrated experimentally:

• Population Bottlenecks Promote Cooperation in Bacterial Biofilms
• Kümmerli R., Gardner A., West S. & Griffin A. S. Limited dispersal, budding dispersal, and cooperation: an experimental study. Evolution 63, 939–949 (2009).

In theory, kin selection should mostly produce adaptations that work on relatedness cues that dynamically take overall population similarity into account. However, kin selection effects must work by manipulating development. Cruder measures of detecting similarity and relatedness will often be employed in practice.

Humans are among those species that have experienced a relatively recent population bottleneck - in the form of the Toba catastrophe. It is intriguing to consider the scale of the resulting increased levels of cooperation between humans that might be the result of this.