Homophily

Kin selection results in greater cooperation between relatives. A side effect of this is greater levels of interaction between similar organisms. A name has been given to this phenomenon: homophily. As the etymology suggests this term means: liking those similar to you. This idea is captured in the proverbial saying: "birds of a feather flock together".

Here's what Wikipedia says on the topic:

Homophily (i.e., "love of the same") is the tendency of individuals to associate and bond with similar others. The presence of homophily has been discovered in a vast array of network studies. More than 100 studies that have observed homophily in some form or another and they establish that similarity breeds connection. These include age, gender, class, and organizational role.

Individuals in homophilic relationships share common characteristics (beliefs, values, education, etc.) that make communication and relationship formation easier. Homophily often leads to homogamy—marriage between people with similar characteristics.

The term was coined in the 1950s. More recently, a significant literature on the topic has developed.

Kin selection seems to have been largely ignored or rejected as an explanation of homophily - apparently because it takes place between similar organisms - who need not necessarily be kin. However a broader interpretation of kin selection that includes memes as well as genes positions kin selection very centrally as a theoretical explanation of homophily. Almost all similarity in nature is based on copying - whether through blood kinship, mimicry, teaching, behavioural imitation or learning in shared environments. The fundamental logic of kin selection is based on copying heritable information - and so it applies to all of these phenomena.

There have been some studies of the evolution of homophily - including one published in Nature. However, this was Funded by the Templeton Foundation, and authored by kin selection hater Martin Nowak. Needless to say, it makes no mention of kin selection. It's proposal is that homophily offers direct fitness advantages. It gives an example: "homophily may yield fitness advantages because individuals using the same mode of communication may be able to act together more effectively". Sure, but a shared communication system is going to be down to shared genes - or shared memes. Kin selection - or cultural kin selection is thus applicable. Normally a cooperative system featuring shared genes or memes would be followed by mention of the work of W. D. Hamilton. Not here, though: this is ideology, not science.

The study of homophily has resulted in a significant literature, most of which bears pretty directly on the topics of kin selection and cultural kin selection. There's quite a lot of quantitative data available on the topic. Many of the studies involve humans as subjects - helping directly with the study of cultural kin selection. So far, the topic has lacked a central organizing principle. Kin selection neatly explains homophily. The study of homophily to date has produced an abundance of highly-relevant data. Now that there's a good theory to ground and guide our observations of homophily, progress in the area should come more rapidly.

References

• McPherson, M., Smith-Lovin, L., & Cook, J. M. (2001). Birds of a Feather: Homophily in Social Networks.
• Retica, Aaron (2006). Homophily. New York Times. Shankar Vedantam (2006) Why Everyone You Know Thinks The Same As You
• Haun, D. B. M., & Over, H. (2013). Like me: A homophily-based account of human culture. [paywall] In P. J. Richerson, & M. H. Christiansen (Eds.), Cultural Evolution: Society, technology, language, and religion.
• Fu, Feng, Nowak, Martin A., Christakis, Nicholas A. and Fowler, James H. (2012) The Evolution of Homophily
• Torkington, Nat (2006) Homophily in Social Software.
• Shalizi, Cosma Rohilla and Thomas, Andrew C. (2010) Homophily and Contagion Are Generically Confounded in Observational Social Network Studies
• Kossinets, Gueorgi and Watts, Duncan J. Origins of Homophily in an Evolving Social Network