how does cooperation evolve?

1
how does cooperation evolve?
cooperation gt group evolution gt natural
selection gt mechanism of evolution of
cooperation is group selection
2
factors determining strength of group selection

• local fitness effects
• genes which give the individual higher fitness
  are selected
• genetic structure
• 
  
  
  groups are defined
  by the sharing genetic structure, i.e.
  cooperation

3
evolution of altruism by group selection (Pepper
Smuts 2000)

• investigate the effects of
• varying ecology
• group selection kin interaction VS group
  selection kin interaction
• alarm calling VS restrained feeding

4
agent-based model

• world
• 2D wrap around lattice
• agents
• plant
• forager

5
model continued
linear

• plant behaviour
• grow
• linear
• logistic
• be consumed

logistic
6
model continued

• forager behaviour
• movement
• same as sugarscape with vision 1 and can move
  into any of 8 cells
• death
• same as sugarscape with forager lifetime
  infinity
• reproduction
• reproduce asexually when energy gt fertility
  threshold
• parent energy - child initial energy
• child born in cell closest to parent

7
model continued

• cooperation
• alarm calling
• feeding restraint

8
model continued
targeted individual
Range around it in which foragers will give alarm
calls
9
model continued
forager has 0.02 probability of being targeted
alarm callers will respond if within 5 cells of
targeted forager probability of kill 1 / ( n
1 ) where n is the number of alarm
callers targeted forager can not make an alarm
call kill population alarm callers targeted
forager a random forager is chosen from the kill
population
10
model continued
Restrained feeders consumption 0.5 plant
energy Unrestrained feeders consumption 0.99
plant energy
50
plant size
99
11
model continued
12
model continued
patch gap width
patch width
13
uniform environment (one plant per cell)
patch width 529 gap width 0
alarm-caller
non-caller
mixed population
pure population
14
uniform environment (one plant per cell)
patch width 529 gap width 0
restraint feeding
non-restraint feeding
mixed population
pure population
15
discussion of results (pure population)
who cares tells us nothing about between-group
selection since there is only one group
16
discussion of results (mixed population)

• local fitness effects
• group selection ignores suboptimisation problem
  within cooperative group (Heylighen 1997)
• fitness(non-cooperators) gt fitness(cooperators)
  
• genetic structure
• cooperative systems eroded from within by
  genetic competition (Campbell 1983)
• mixed population gt non-cooperative genes
  selected
• gt local fitness and genetic structure effects
  not strong enough for group selection to occur

17
variable environment (mixed population)
population 0.5 alarm caller 0.5 non-alarm
caller
18
variable environment (mixed population)
population 0.5 restraint feeder 0.5
non-restraint feeder
19
discussion of results (mixed population)

• local fitness effects
• population size must be small (Futuyma 1986)
• small patch width high gap width gt many small
  population groups
• groups a
• (cooperators) gtgt (non-cooperators)
• groups b
• all other groups fit into groups b

20
discussion of results (mixed population)

• local fitness effects continued
• altruistic group has higher fitness due to
  synergy of cooperation (Heylighen 1997)
• fitness(groups a) gt fitness(group b)

21
discussion of results continued (mixed population)

• genetic structure
• there can not be significant gene flow (Futuyma
  1986, Goldstein Zimmerman 2000)
• migration rates must be implausibly low (Ridley
  1993)
• low patch size high gap width low vision
• gt low probability of migration gt gene flow
• gt reduced probability of non-cooperator
  infiltration of groups a

22
discussion of results continued (mixed population)

• genetic variance continued
• successful groups must be able to export their
  local productivity from the local area (Wilson et
  al 1992)
• patch full gt steady emigration
• fitness(cooperator) gt (non-cooperator) gt
  higher probability of successful colonisation for
  cooperators than non-cooperations
• difficulty of migration gt infiltration of
  non-cooperators low
• gt local fitness and genetic structure effects
  are strong enough in some scenarios for
  group-selection gt cooperation evolves

23
variable environment (mixed population absence
of kin assortment)
alarm calling never evolved in any of the 100
runs BUT restraint feeding did
24
discussion of results (mixed population absence
of kin assortment)

• local fitness
• alarm calling can only spread if foragers are
  heavily recompensated by others increasing their
  fitness relative to themselves (Wilson 1979,
  1980)
• recompensation comes through spatial
  association to cooperators
• cooperators ltgt kin
• spatial association was removed largely by
  randomising birth locations
• fitness(alarm callers) lt fitness(population)

25
discussion of results (mixed population absence
of kin assortment)
local fitness continued however, feeding
restraint conferred benefits as well as costs on
the bearer gt fitness(restraint feeders) gt
fitness(alarm-callers)
26
discussion of results continued (mixed population
absence of kin assortment)

• genetic structure
• kin selection increases genetic selection
  between-groups and decreases it within-groups
  (Smith 1964)
• spatial association ltgt kin discrimination
• randomised birth starting location
• gt kin selection was not operating
• gt selection between-groups was reduced

27
discussion of results continued (mixed population
absence of kin assortment)
genetic structure continued migration rates must
be implausibly low (Ridley 1993) there can not
be significant gene flow (Futuyma 1986, Goldstein
Zimmerman 2000) random birth locations gt
mixed population gt gene flow gt non-cooperators
selected over cooperatots gt local fitness
effects and genetic structure are not enough for
between-group selection to occur for alarm
callers
28
discussion of results continued (mixed population
absence of kin assortment)
genetic structure continued however restraint
feeders were selected when patch width low and
gap-width high small group size gt restraint
feeder becomes an increasing proportion of the
acts recipients gt kin selection was not
needed gt local fitness effects and genetic
structure were strong enough for the evolution of
feeding restraint
29
summary

• evolution of cooperation
• favored by group-selection
• diminshed by within-group selection
• evolution of cooperation is dependent on
• ecological patchiness
• small patches and large gaps stabilise
• degree of migration
• strong vs weak altruism

30
critique

• kin selection
• there was no kin discrimination rule but the
  rule is defined in biology
• reproduction
• reproduction was asexual and the offspring were
  the genetic clones of their parents whereas the
  rules of genetics are well established
• movement
• movement rule had vision of 1 which made
  migration difficult if not impossible

31
critique continued

• model parameters
• the starting population size was 40 which is
  small
• the size of the world was not given, the
  assumption is x y 527 which is small
• death
• foragers lived forever, a more realistic life
  expectancy was given in sugarscape
• simple
• not a very sophisticated model

32
references
d. j. Futuyma, evolution biology, 1986 t. h.
Goldsmith, w. f. Zimmerman, biology, evolution,
and human nature, 2000 f. heylighen,
http//pespmc1.vub.ac.be/COOPGEVO.html, genetic
scenarios for evolving cooperation, 1997 j. w.
Pepper, b. b. Smuts, the evolution of cooperation
in an ecological context an agent-based model,
2000 m. Ridley, evolution, 1993