Transcript The Origin of Species

The biological roots of altruism
Vidyanand Nanjundiah
Indian Institute of Science
Annual Day
Alexander von Humboldt Association
Bangalore, 300911
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
Asexual life cycle of Dictyostelium discoideum
a
c
b
d
h
g
f
e
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
Growth rates (46a3, 46d2)
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
Tempo of development (46a3, 46d2)
46a3
46d2
Mix
2 hr
4 hr
6 hr
8 hr
Scale
46d2 also develops slower than 46a3
24 hr
250 µm
1 mm
Relative efficiency of sporulation (46a3, 46d2)
Spore forming efficiency of 46a3 in presence of 46d2.
Percent of D. giganteum 46a3 spores
100
80
60
40
20
0
0
20
40
60
80
Percent of D. giganteum 46a3 amoebae
100
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
Geography
1/5
6/8
<
<
2/8
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).
Simpson’s Paradox in a Synthetic Microbial
System
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
Chuang, et al., Science 323, 272-275, 2009)
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 pi ’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