Tuesday, November 26, 2013

Nowak and colleagues skewer Inclusive Fitness

Allen at al Fig 2 (see text below)
Martin Nowak sends me a new PNAS paper called "Limitations of inclusive fitness" which he as co-authored with EO Wilson and Benjamin Allen. This shows that:
inclusive fitness is ... a limited concept, which exists only for a small subset of evolutionary processes. Inclusive fitness assumes that personal fitness is the sum of additive components caused by individual actions. This assumption does not hold for the majority of evolutionary processes or scenarios. To sidestep this limitation, inclusive fitness theorists have proposed a method using linear regression. On the basis of this method, it is claimed that inclusive fitness theory (i) predicts the direction of allele frequency changes,(ii) reveals the reasons for these changes, (iii) is as general as natural selection, and (iv) provides a universal design principle for evolution... all of [these claims] are unfounded. If the objective is to analyze whether mutations that modify social behavior are favored or opposed by natural selection, then no aspect of inclusive fitness theory is needed.
 Strong words, but the text supports this. They point out that additivity seldom holds, and once you are in the realm of linear regression you confuse correlation with causation.  In particular they offer three compelling mathematical counter-examples:
  1. The Hanger-On (purple)who finds a high-fitness partner to interact with. The regression recipe yields B > 0, C < 0 misinterpreting this behaviour as beneficial cooperation.
  2. The Jealous Individual (red) who attacks an individual of high fitness. This attack reduces the recipient’s fitness from 5 to 4, and the attacker's fitness from 1 to 0. The regression recipe yields B ,C > 0, misinterpreting this attack as costly cooperation.
  3. The Nurse (blue)who helps an individual of low fitness. This aid increases the recipient’s fitness from 0 to 0.5 (representing a 50% chance of having an offspring), and decreases the nurse’s fitness from 1 to 0.5. The regression recipe yields B < 0, C >  0, misinterpreting this aid as costly harming or spite. 
It will be interesting to see what the Inclusive Fitness crowd make of it. I expect they will simply question the provenance of the authors (two Catholics and an old man) because the arguments seem unanswerable.

PS Though I'm informed that one of the alleged "Catholics" isn't in fact a Catholic, although he works at a Catholic University. Of course Mendel was a Catholic and Fisher was a staunch Anglican and the whole point about science is that the conclusions do not depend on the person of the authors.

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