The biological roots of altruism

Annual DayAlexander von Humboldt Association

Bangalore, 300911

Vidyanand NanjundiahIndian 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 (wi, zi)] clearly

distinguished from within-group [mean (wi Δzi)] effect

w. Δz = cov (wi, zi) + mean (wi Δzi)

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

efgh

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)

46a3 3.40 ± 0.08

46d2 4.06 ± 0.01

 Mean ± s.d., n= 4, t test, p< 0.05

46a3 grows significantly faster than D. gig. 46d2

Growth rates (46a3, 46d2)

46d2

2 hr 8 hr 24 hr4 hr 6 hr

Scale 250 µm1 mm

46a3

Mix

Tempo of development (46a3, 46d2)

46d2 also develops slower than 46a3

Relative efficiency of sporulation (46a3, 46d2)

0

20

40

60

80

100

0 20 40 60 80 100

Perc

ent o

f D. gig

ante

um

46

a3 s

pore

s

Percent of D. giganteum 46a3 amoebae

Spore forming efficiency of 46a3 in presence of 46d2.

46a3 does worse than 46d2Black 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, 272-275, 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 Δpi 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