Download animal altruism

Animal Altruism
Altruism occurs when the giver suffers a fitness loss while the recipient experiences a fitness
gain. “Loss” could be trivial (you wasted seconds of my time) or significant (sacrificed my life)
Peter Kropotkin
1842-1921, Russia
• Born Prince Kropotkin, became disgusted with
contrast between the extravagances of court life
and the poverty of Russian peasants.
• Studied biology and geography; volunteered for expedition to eastern
Siberia. Expected Darwin’s prediction of competition, instead saw
cooperation in both society and nature.
• Published Mutual Aid: A Factor of Evolution in 1890 as a rebuttal to
T.H. Huxley and other social Darwinists.
• Travels to join international workers movements; survives prison in
Russia, assassination in London, arrest in Paris. deportation from
Switzerland. In 1917 returns to Russia for revolution, but stops when
the Bolsheviks come to power.
Some of Kropotkin’s examples can be
explained away by “kin selection”
Since worker bees are sterile clones,
its easy to see how they can sacrifice
their life and still propagate their
genes.
It is not so much “altruism” on the
part of the bee but rather selfish selfinterest on the part of the genes.
Hence the title of Dawkin’s book,
“The Selfish Gene”
Some of Kropotkin’s examples can be
explained away by “kin selection”
You share ½ your genes with a sibling, 1/8th with cousin.
r = the genetic relatedness of the recipient to the giver
B = reproductive Benefit gained by the recipient
C = the reproductive Cost to giver
Kin selection predicts rB > C must hold for altruism to occur
J.B.S. Haldane: “I would willingly die for two brothers or eight cousins.”
Red squirrels: surrogate mothers adopt related orphaned squirrel pups but not unrelated
orphans. Cost = decrease in survival probability of the litter. Benefit = increased chance of
survival of the orphan. Females always adopted orphans when rB > C, but never adopted when
rB < C.
Some of Kropotkin’s examples
CANNOT be explained away by “kin
selection”
• Dogs often adopt orphaned cats, squirrels, ducks, etc.
• Dolphins support sick or injured animals in water
• Chimpanzees will help humans and conspecifics without any reward
in return.
• Birds such as Mexican Jays will help feed young unrelated to them.
• Birds will given alarm calls in flocks of mixed species.
• Lemurs of all ages and of both sexes will take care of infants
unrelated to them.
The Iterated Prisoner’s Dilemma winner: Rapoport’s
tit for tat
The first time meeting a program, cooperate
The next time, repeat what it did last time.
If T4T meets itself, they cooperate
If T4T meets defect-only, it only gets fooled once
If T4T meets random chooser who defects, (eg JOSS), it will
retaliate on the next move (often when JOSS cooperates, thus
lowering JOSS score)
Many variations on this are possible: “tit for two tats” for
example. All must cooperate first, retaliate eventually, and
forgive eventually to qualify.
Tit-for-Tat Bats
The vampire bat:
individuals which feed
blood are much more likely
to get fed themselves.
Distribution of risk: best place to store extra food is
in the belly of your neighbor
Reciprocal altruism in interspecies
cooperation: cleaner wrasse
• Cooperating: Cleaners eat
ectoparasites, clients benefit from
being cleaned
• Defecting: cleaners eat client
mucus/tissue instead of parasites;
clients eat cleaners
• Threat of retaliation increases
cooperation: Predatory clients are
cheated less often than nonpredatory clients because they cast a
“shadow of the future”. Cleaners who
cheat are chased away.
• A biological market: reputation
effects determine levels of service–
just like ebay!
Indirect reciprocity
Japanese macaques: low-ranking monkeys that groom
high-ranking ones (which have good reputations) may
better their own reputations. Simply being seen with
the top brass improves probability you will be
groomed.
One fish, two fish, cooperate with you fish
Stickleback fish:
“scouting” near potential
predator is a risk, but helps
group determine when it is safe to leave for hunting.
Stickleback are more likely to do scouting if they have
evidence of other scouts: recall Orstom’s “contingent
cooperators”
Spatial selection in the Acorn Woodpecker
Acorn Woodpecker:
Why don’t “free riders”
rise in genetic
frequency?
Recall Orstom’s “clearly
defined boundaries”:
a group of cooperators could out-compete a group of
non-cooperators (Nowak).
Acorn Woodpecker
Acorn Woodpecker:
Why don’t “free riders”
rise in genetic
frequency?
•
•
•
•
•
r = the genetic relatedness of the recipient to the giver
B = reproductive Benefit gained by the recipient
C = the reproductive Cost to giver
Kin selection predicts rB > C must hold for altruism to occur
“Cooperative Selection” violates this rule!
Yeast and spatial selection: survival of the fastest
Yeast comes in two forms: enzyme producers
And those who sponge off the enzyme producers
In a homogeneous mix, the
Enzyme producers die out.
In clumps, little islands of
cooperation form.
Cooperators alone replicate faster, so they out-compete
the free-loaders.
http://www.cell.com/current-biology/abstract/S0960-9822(13)00434X?_returnURL=http%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS096098221300434X%3Fshowall%3Dtrue
Does group selection exist?
Many biologists insist that it cannot. A gene that
causes you to sacrifice yourself “for the greater
good” would surely die out.
Others point out that empirical evidence is to the
contrary. We consistently find a deep instinct for
altruistic behavior, even between different
species.
Inter-species altruism
Osprey feeding Slender
Billed Gull (BBC). Perhaps
a “pathology”?
Is nature as ruthlessly competitive as evolutionary
biologists have theorized? Perhaps altruism can “err on
the side of caution” and still be an Evolutionarily Stable
Strategy. What if we “cooperate on the first move”?
Friends Furever
Summary: 5 ESS* for cooperation
1. Kin selection: not really cooperation, just gene
selection via kin. Red squirrels.
2. Direct reciprocity: tit for tat bats.
3. Indirect reciprocity: high ranking monkeys
4. Spatial selection: Survival of the fastest
5. Group selection: perhaps even between
species?
*Evolutionarily Stable Strategies