Transcript Nature

From genes to societies
A biologist’s view on
conflict and cooperation
Economic Game theory
Oskar Morgenstern
John von Neumann
John Nash
John von Neumann & Oskar Morgenstern (1944) Theory of Games and Economic Behavior
Evolutionary Game theory
Maynard Smith (1986) Evolution
and the Theory of Games
Applied logic of economic game
theory to biological systems
Blind process of natural selection
no longer required rationality
assumption
“Let nature do the work and see
what happens”
Outcome was as if agents were
rational, self-interested fitness
maximizers
Evolutionarily stable strategy (ESS)
wild type
rare mutant
x
x
mutation
mutation
x
x
reproduction
reproduction
selection
selection
does better than
is not an ESS
cannot invade
is an ESS
Evolutionary stable state
and
may also end up coexisting in
the population in some equilibrium frequency
occurs at the point where they have equal fitness
such a stable polymorphic state is an
evolutionary stable state
Maynard Smith 1986 Evolution and the Theory of Games
Example: hawk-dove game
Two types: hawks and doves
Doves share a resource peacefully, hawks fight over it
B=value of the resource, C=cost of fighting another hawk
Individual 1
Individual 2
dove
hawk
dove
B/2
0
hawk
B
(B-C)/2
Result:
ESS is to play hawk with probability B/C
or evolutionary stable state with fraction B/C hawks
Maynard Smith & Price Nature 1973
The Logic of Animal Conflict
Strategists can be genes, cells,
organisms or societies
Maynard-Smith, J., Szathmary, E. 1995. The major transitions in
evolution. Cambridge UP.
Independent replicators
Linked replicators in single cell
Multicellular organisms
Societies
Plan of my talk
- Illustrate biological conflicts at various levels
- What causes the conflicts?
…why do evolutionary interests differ
- How are conflicts resolved?
…how can wasteful conflict be prevented
- Can we apply this sort of thinking to humans?
Richard Dawkins
Handy shortcuts
- “An organism should want to do this or that”
means
“A gene that makes it do that should spread”
- “The interests are for it to…”
means
“That’s it’s ESS”
- does not imply any moral judgement
1. Conflicts in the genome
The basis for the conflict (1)
Mendel’s first law:
genetic variants segregate
and randomly reunite
Means that 2 genes at a locus
should have equal chances
of being passed on
But any gene would do better if
it would be transmitted to
more than ½ of the gametes
I.e. there is a conflict between
two genes at a locus
Peacock et al. 1972
Genes that beat Mendel’s laws
Normal
w = wild type
SD in fruit fly
w w
w D
D = distorter
Sperm Production
w
w
w
D
Genes that beat Mendel’s laws
Normal
w = wild type
SD in fruit fly
w w
t in the mouse
w D
w D
D = distorter
Sperm Production
w
w
w
w
w
D
w
D
w
D
Copulation
Inside Female
D
The basis for the conflict (2)
Nuclear genes
inherited from mother + father
transmitted through both sexes equally
Leda Cosmides & John Tooby
Cytoplasmic inheritance and intragenomic conflict
1981 J. Theor. Biol.
Mitochondrial genes
ancient bacteria (ca. 2 BY BP)
maternally inherited
transmitted through females only
male=dead end
Evidence
ca. 4% of all hermaphrodite
plants carry mitochondrial
gene resulting in male sterility
no pollen, but increased seed
production
nuclear genes may restore
male sterility
Saumitou-Laprade et al. 1994
Wolbachia bacteria
1. Kill all males 2. Turn males into females
3. Make males
unnecessary Infects reproductive tissues of
insects and arthropods
Only maternally transmitted
Benefit production of females at
the expense of males
O’Neill et al. 1999 Influential Passengers
Conflict 3: jumping genes
transposons can “jump”
from one place to
another in the genome
(cut and paste)
make up 10% of our
genome
serve no useful purpose
What resolves the conflict?
Organisms usually seem to function
reasonably well. Why?
Egbert Leigh (1977) Proc.Natl.Acad.Sci. USA
Parliament of the genes
Selfish genes frequently cause cost to
whole organism
Hence genes at other loci are selected
to suppress the effect of selfish genes
Causes conflicts to be resolved in favour of collective interests
2. Conflicts in the family
Kin selection
Hamilton’s rule (J. Theor. Biol. 1964)
B.r  C
Cost to actor
Benefit to receiver
Relatedness
JBS Haldane
“I would be willing to lay down my life for 2 brothers or 8 cousins.”
r to offspring = ½ : you should love your children
Basis for the conflict
Robert Trivers (1974)
Mother equally related to all
offspring (r=0.5)
But offspring value themselves (r=1)
more than siblings (r=0.5)
Consequence:
sibling conflict +
parent-offspring conflict
Trivers Am. Zool. 1974
Siblicide
Spadefoot toads
Masked booby
Sand tiger sharks
Kittiwake gulls
Piglets
Indian rosewood
How is the conflict resolved?
- High relatedness
Briskie et al. 1994
passerine birds: chicks beg less
when they are more related
9-banded armadillo: clonal offspring
- Parental disciplining
possible because of power asymmetry
may be costly in itself
blue footed booby vs. masked booby
Lougheed & Anderson 1998
3. Conflicts in superfamilies
Insect societies
SOCIAL INSECTS
COOPERATE
But there should also
be conflict
William D. Hamilton
"The Genetical Evolution of Social Behaviour"
(1964, J. Theor. Biol.)
Kin selection theory
Individuals are selected to help kin
but be nasty towards nonkin
Robert Trivers & Hope Hare
“Haplodiploidy and the Evolution of Social Insects"
(1976, Science)
Relatedness asymmetries in social insect
colonies should lead to a variety of
conflicts
Conflict 1
WORK
REPRODUCE
BENEFIT
increased colony efficiency
obtain direct reproduction
COST
no direct reproduction
reduced colony efficiency
(laying workers do not work)
Wenseleers, Helantera & Ratnieks 2004 J. Evol. Biol.; Wenseleers et al. 2004 Am. Nat.
Ratnieks & Visscher Nature 1989
level of selfishness
(% of reproductive workers)
Polistes chinensis
20
15
Dolichovespula saxonica
Vespula rufa
10
D. sylvestris
D. norwegica
D. media
5
Vespa crabro
Vespula vulgaris
0
Spearman rank R = -0.92, p = 0.0005 Apis mellifera
60
70
80
90
100
effectiveness of policing (%)
Log10(% males workers' sons+1)
36
2.0
n=68 species
ANTS
BEES
WASPS
9
8
56
7
52
35
34
1.5
POLICING
Workers most related
to queen’s sons
33,37,43
59
NO POLICING 55
28
41
Workers most related
26
65
10
to other workers’
sons
60
1.0
58
30
25
31
29
4
5
0.5
50
61
1
6
39
51
63
0.0
49
48
-0.15
Wenseleers & Ratnieks 2005
22-23
21
11 66
-0.10
24 13 12 64
-0.05
57 14 27 62
0.00
2
0.05
70
3,15-20,32,38
40,42,44-47
53-54,68
67 69
0.10
relatedness to
workers' vs. queen's sons
0.15
Conflict 2
female larva
BECOME WORKER
BECOME QUEEN
BENEFIT increased colony efficiency
greater direct reproduction
COST
reduced colony efficiency
(queen overproduction)
less direct reproduction
Wenseleers et al. J. Evol. Biol. 2003; Ratnieks & Wenseleers Science 2005
The struggle to become a queen
Q
Melipona stingless bees
ca. 20% become queen
Q
matches predicted ESS
almost perfectly
Q
Q
Q
Ratnieks & Wenseleers Science 2005
Conflict very costly: queens killed
Wenseleers et al. 2003, 2004
Honeybee: worker fate enforced
“Power” to the adult workers
How are conflicts in
insect societies resolved?
- High relatedness
may limit conflict, but only partially effective
- Mechanisms of coercion
good for the colony
…but not so nice for the oppressed individuals
Ratnieks, Foster & Wenseleers 2006 Ann. Rev. Entomol.
4. Sexual conflicts
The battle of the sexes
Male-male competition (1)
Male-male competition (2)
Abele, L.G. and S. Gilchrist. 1977. Homosexual rape and sexual
selection in acanthocephalan worms. Science
Battle between the sexes (1)
When is there a conflict-of-interest between
the sexes?
1. Males ensure paternity by causing
harm to females
Bean beetle males
harm females
Crudgington & Siva-Jothy Nature 2000
Seminal toxins in the fruit fly
Male injects female with toxin
Sedates female and prevents
her from mating with other
males
But costly to female:
shortens her lifespan
Chapman et al. Nature 1995
Battle between the sexes (2)
When is there a conflict-of-interest between
the sexes?
1. Males ensure paternity by causing harm
to females
2. Conflict over sex roles
choosiness, parental invesment
Conflict over sex roles
Typical sex roles come about because of differences
between the sexes in investment in individual offspring
FEMALES
Invest a lot in each offspring (eggs, gestation, lactation, care)
Cannot have large numbers of offspring
Cannot greatly increase fitness by having multiple partners
Usually can increase fitness by being choosy
MALES
Invest little in each offspring
Can have large numbers of offspring
Can greatly increase fitness by having multiple partners
Rarely can increase fitness by being choosy
Angus John Bateman
Robert Trivers
Eager males and choosy females
# fertilisable females < sexually active males
(♂-biased operational sex-ratio)
selects for “eager” males and “choosy” females
males should frequently want to mate with females
when they don’t want to
females should reject low-quality males
Coercive sex
Not enforced
Long courtship
Enforced
No courtship
Struggle
Alcock 2000
Iron cross blister beetle
Female counterdefence
Dunnocks: eject sperm
of low-status males
Davies Nature 1983
Sexual arms race
water striders
n=15 species
Arnqvist & Rowe Nature 2002
Sex role reversal: wattled jacana
Male uniparental care
Causes male to carry most of
the cost of offspring production
Results in choosy males and
ornamental, eager females
Emlen et al. 1998
Penis fencing in hermaphrodites
both want to become the male
(minimum investment)
first one who is stabbed by the
other’s penis becomes the female
and has to produce expensive eggs
Pseudobiceros hancockanus
Michiels, N.K., and L.J. Newman. 1998. Sex and violence in hermaphrodites. Nature 391(Feb. 12):647
Penis chewing in banana slug
the one whose penis is bitten off
first becomes the female
can take 12 hours
A.B. Harper 1988, B.L. Miller 2005
How is the conflict resolved?
- Of all biological conflicts the hardest to resolve
- Optimum for one sex frequently diametrically
opposed to optimum for other sex
- Can result in endless arms-race
- Exception: strict lifetime monogamy
Links fitness interests of both sexes
Swans
Angler fish
male
5. Conflicts in human society
“They are in you and me; they created us,
body and mind; and their preservation is the
ultimate rational for our existence. They
have come a long way, those replicators.
Now they go by the name of genes, and we
are their survival machines.”
Richard Dawkins (1976) The Selfish Gene
Attitutes towards sex
Clark & Hatfield J. Psych. Hum. Sex. 1989
Males
“Would you go to bed with me tonight?”
“Would you go out with me tonight?”
Females
Attitutes towards sex
Clark & Hatfield J. Psych. Hum. Sex. 1989
“Would you go to bed with me tonight?”
“Would you go out with me tonight?”50%
Males
75%
56%
Females
0%
Attitutes towards sex
Clark & Hatfield J. Psych. Hum. Sex. 1989
“Would you go to bed with me tonight?”
“Would you go out with me tonight?”50%
Males
75%
56%
Females
0%
Schmitt et al. J. Pers. Soc. Psych. 2003: human universal
Tesser Psych. Res. 1993: ca. 50% heritable
1960s: contraception
decision to have a child came into
the hands of woman
…and love could be free
Hera Cook (2004) The Long Sexual Revolution
English Women, Sex, and Contraception 1800-1975
Disclaimer !!!!!!!!!!!!
To argue that what is natural is ‘right’ is
to commit the naturalistic fallacy
George Edward Moore (1903)
Principia Ethica
“Let us understand what our own selfish
genes are up to, because we may then at
least have a chance to upset their designs,
something that no other species has ever
aspired to do.”
Richard Dawkins (1976)
The Selfish Gene
Unique features of human society
Most cooperative interactions are between
genetic strangers
High cognitive abilities
Many traits are culturally determined and
acquired through immitation and learning
What consequences does this have for the
evolution of conflict?
1. High cognitive abilities
Increases scope for cooperation :
cooperate with others who have a good reputation
B.q > C
Nowak & Sigmund Nature 1998
q = prob. of knowing status of others
repeated interaction: TIT-FOR-TAT
cooperate with others who cooperated before
B.p > C
Axelrod & Hamilton Science 1981
p = prob. of meeting again
What about nurture?
“My father was a relentlessly self-improving boulangerie
owner from Belgium … When I was insolent I was
placed in a burlap bag and beaten with reeds - pretty
standard really.”
2. Culture
Should culture make us nicer than what you would predict from our genes?
Gene-culture coevolution / meme theory
Spread of ideas or beliefs can be analyzed in same way as spread of genes
Cultural transmission can be vertical (parents), horizontal (peers) + oblique
Relatively high mutation rate compared with genetic evolution ~ 1%
Luca Cavalli-Sforza
Marcus Feldman
Robert Boyd
Pete Richerson
Culture can be maladaptive
Beliefs (“memes”) that are biologically maladaptive can spread
Boyd & Richerson (1985, 2005) :
2 memes E = marry early, short education, many children
L = marre late, long education, few children
Long education meme L spreads if
A.t > (1-A).p
where
A and 1-A = relative influence of teachers and parents
t = how much holding the late marrying meme increases chance of becoming a teacher
p = how much holding early marrying meme increases probability of being a parent
If A = 0 then late marrying meme would not be able to spread
But if A > 0 (teachers have some influence) it might well do
cf. demographic transition
Example: religion
Religious beliefs tend to spread as a result of
active church proselytizing, but the values that
are thought (e.g. fairness, altruism, generosity,
etc.) invariably are ones which serve society,
not individual self-interest.
“God memes survive not because they are true in
any metaphysical sense. No, they have survived
because they are selfish memes and are good at
surviving – they need no other reason.”
Susan Blackmore (1999)
The Meme Machine
Vertical transmission of beliefs
religion is primarily
maternally transmitted
Cavalli-Sforza et al. Science 1982
celibacy of male priests actually
does not harm the transmission
of religion
Religion and “pro life” values
The battle for souls (Roof & McKinney 1987)
US: Conservative Protestants win out despite net losses due to
conversion to other religions
Due to “pro life” values !
# births / woman
(under 45)
Conservative Protestants
2.01
Catholics
1.82
Liberal Protestants
1.60
Jews
1.37
Secular
1.18
“Darwinians can take perverse comfort in the idea that the main reason that
conservative Protestants are succeeding in the US is natural selection!”
Richerson & Boyd 2000
Conclusion
Many factors can make us more cooperative
than our animal cousins:
- high cognitive abilities allow reputationbased cooperation and reciprocation
- social norms may spread that are
biologically maladaptive
- (the law)
And remember…
Behavioural genetics
Variance in traits can be partitioned Vtot=Vg+Vse+Vne
heritability=Vg/Vtot=correlation in behaviour between MZ twins reared apart
Genetic
heritability
(own genes)
Shared
environment
(parental)
Nonshared
environment
(peers, culture)
Adult body height
78%
11%
11%
Neuroticism
50%
0%
50%
Social responsibility
42%
23%
35%
Religiosity
21%
46%
33%
12%
51%
37%
(church attendance)
Religious affiliation
Silventoinen et al. Twin Res. 2003; Bouchard & McGue J. Neurobiol. 2003;
D’Onofrio et al. J. Pers. 1999; Kendler et al. Am. J. Psych. 1997; Rushton Proc. Roy. Soc. 2004
Male strategies in a marine isopod
Paracerceis sculptamale
3 morphs
have equal fitness
1 genetic locus involved
“Alpha”
(fighter)
“Beta”
(female
mimic)
“Gamma”
(hider)
Shuster & Wade Nature 1991
Male morphs in side-blotched lizard
orange
blue
yellow
Sinervo & Lively Nature 1996
Evolutionary game
Orange throated males: hold large territory with several females
Yellow striped males: mimic females, can sneak into large territories
Blue throated males: defend small territory with one female, not fooled by yellows
Evolutionary game:
blue beats yellow, yellow beats orange, orange beats
results in 5 year cycles
Large Territory Holders
Defenders
Sneakers
Rapid evolution of male genitalia
Arnqvist Nature 1998