The biological roots of altruism Annual Day Alexander von Humboldt Association Bangalore, Vidyanand Nanjundiah Indian Institute of Science

Assumption I Human beings are products of evolution Evolution works via modification with descent Therefore anything ‘human’ likely has a biological basis rooted in our ancestry

The problem that haunted Darwin …one special difficulty, which at first appeared to me insuperable, and actually fatal to my whole theory. I allude to the neuters or sterile females in insect-communities…from being sterile, they cannot propagate their kind. The Origin of Species; Chapter 7 - Instinct

Assumption II The explanation involves natural selection

Darwin’s first solution: “Kin selection” …selection may be applied to the family, as well as to the individual… … a well-flavoured vegetable is cooked, and the individual is destroyed; but the horticulturist sows seeds of the same stock, and confidently expects to get nearly the same variety… Chapter 7 - Instinct

Darwin’s second and third solutions: multicellular development I believe that natural selection, by acting on the fertile parents, could form a species which should regularly produce neuters… We can see how useful their production may have been to a social community of insects, on the same principle that the division of labour is useful to civilised man. Chapter 7 - Instinct

Darwin’s fourth solution: group selection if …one tribe included a great number of courageous, sympathetic and faithful members, who were always ready to warn each other of danger, to aid and defend each other, this tribe would succeed better and conquer the other. Descent of Man and Selection in Relation to Sex Chapter V – On the Development of the Intellectual and Moral Faculties

Post-Darwin I Reciprocal altruism Handicap principle

Post-Darwin II Price: Between-group effect [cov (w i, z i )] clearly distinguished from within-group [mean (w i Δz i )] effect w. Δz = cov (w i, z i ) + mean (w i Δz i ) Pop. fitness Pop. change in trait Fitness of group I Trait value in group i Crucial point: covariance between group fitness and trait value. The second term on the right is <0 (by assumption); can the first make up and yield an overall positive value for Δz ? First suggestion of possible necessary condition.

Are there alternatives to close genetic relatedness as the dominant factor behind altruistic behaviour?

Alternative 1 Trade-offs

a b c d e f g h Asexual life cycle of Dictyostelium discoideum Sexual macrocysts formed by D. giganteum

Natural CSM groups form by ‘choice’ and tend to be genetically heterogeneous

How do strains behave vis-à-vis one other? Experimental test: compare them pair wise

Strain Generation time (hours) 46a ± d ± 0.01 Mean ± s.d., n= 4, t test, p< a3 grows significantly faster than D. gig. 46d2 Growth rates (46a3, 46d2)

Tempo of development (46a3, 46d2) 46d2 also develops slower than 46a3

Relative efficiency of sporulation (46a3, 46d2) 46a3 does worse than 46d2 Black line: null hypothesis; Red line: experimental data

Conclusion Combination of selection at different life-history stages within and between groups Trade-offs

Alternative 2 Stochastic effects

Simpson’s paradox: Faculty recruitment at the University of California, Berkley Men Women (Number selected/number who applied) History 1/5 < 2/8 Geography 6/8 < 4/5 University 7/13 > 6/13 Implication: Each of the two departments favours women over men; but taken together, they favour men over women. Based on Sex Bias in Graduate Admissions: Data from Berkeley (Bickel et al., Science 187: 398 – 404, 1975).

Chuang, et al., Science 323, , 2009) Engineered E coli cells. Producer: Makes membrane-permeable auto-inducer constitutively; AI induces chloramphenicol resistance gene; Non-producer: Cannot make AI but can respond similarly to externally provided AI Simpson’s Paradox in a Synthetic Microbial System

In absence of antibiotic (-Cm), non-producer grows slightly better than producer; With antibiotic (+Cm), non-producer grows poorly unless provided with autoinducer

Data from different experiments after single cycle of growth of mixed sub-populations with various starting p i ’s Next figure shows Δp i values in the same experiments (all <0)

Globally, the frequency of producers goes up

Conclusion Cooperation in social groups, even ‘altruistic’ behaviour, is favoured by close relatedness. However, close relatedness is not a prerequisite for cooperation. The roots of altruism may lie in sociology as much as biology