Week 11/12- altruism and human behaviour

Behaviour evolves like ___

any other phenotype: theres variation, heritability, influences fitness, etc.

• Why do particular behaviours evolve as adaptations?

• ie. genes of domestication; long running study where they selected for the most docile foxes in each generation, then took the genes of the offspring and compared to midparent score to see if theres some genetic correlation.

Plant behaviour: challenge to diecious

• accidental selfing → inbreeding depression

• female structure can accidentally knock pollen off bee’s body, or off the style preventing breeding.

• To avoid this:

  • self-closing stigma, which, once pollen enters, it closes to prevent it from being knocked off. If they don’t recieve pollen, they’ll reopen.

Within-species behaviour (unlike between-species interactions)

• mutual benefit

• selfishness

• altruism (why has it evolved??) = behaviour that is negative for actor, but positive effect with the individual it interacts with

• spite (why??)

Evolutionary stable strategy

social conditions → behavioural strategy. Leads to:

evolutionary stable strategy - behaviour that, when adopted by the majority of the population, can’t topped by another strategy (no other strategy has higher fitness)

• ie. lizards, the ESS is having a balance of all 3 colours. if we chose a different strategy, like overloading on blue lizards, then they would immediately get stopped by the orange that can win over them, then the yellows would win over the orange..

Frequency dependant selection and the lizards strategies

fitness depends on the irelative frequency of other phenotypes in the population (negative freq. dependant selection → minority advantage) (positive freq → majority advantage)

lizard example:

• orange = big and agressive

• blue = only mate with one individual and work together to defend

• yellow = sneaker and pretend to be women to mate.

• The success of each one depends on how many of the other lizards there are (orange beats blue in getting territory, blue beats yellow in excluding sneakers, yellow beats orange by pretending to be theri females)

Altruism

traits that decrease the fitness of individual with the trait (cost to donor), but increase the fitness of the other individual (benefit to recipient)

• ie. belder’s ground squirrel live in groups, and one of them raises the call when they spot a predator. This makes them twice as likely to get captured than noncallers, but they stilll do it.

• Adult females are most likely to raise the call because they live in matriarchal communities, and therefore have high relatedness to their colony here. Males disperse to new communities when they mature, and don’t share relatedness with as many of them, so do not have an incentive to raise the alarm)

direct/indirect/inclusive fitness and kin selection

direct fitness = organisms own reproductive success

indirect fitness = reproductive success of genetic relatives facilitated by your actions

inclusive fitness = direct fitness + indirect fitness

kin selection = selection coming from indirect benefits of helping relatives.

How to calculate relatedness

multiply 0.5 for every step through the pathway between individuals

• then add up the two halves (if they’re on the same level- siblings, grandchild-grandchild, etc.)

• parents = 0.5 to kids

• siblings = 0.5 to eachother

• grandparent to grandchild = 0.25

Hamilton’s rule to altruism

(relatedness to recipient)(Benefit to recipient) > (Cost to donor)

• then it will evolve!

for instance: can help parents raise children to increase indirect fitness (helps children survive) as opposed to making your own kids.

• benefit = with helper - without helper (difference between having helper and not)

• cost = what helper could have had - what helper has if they help

Eusociality in insects

eusocial = social organization where there are:

• sterile workers that labour on behalf of reproductive individuals

• sterile workers that cooperate in the care of young.

Its because the females are all sisters. Sons are r=0.5 to the queen, and sisters are related 0.75 to eachother, and 0.25 to brothers.

• so females are helping eachother (their future queens) by raising the babies, and just so happen to be helping the queen.

Cooperation and cheating

slime moulds, if resources are low, some of the moulds will cooperate n=and become part of a non-reproductive stem, and the rest make spores that can spread when the time is right.

• cheating behaviour evolves: some individuals never pay their turn

• made cheating genotypes

• but then the slimes stopped doing any social behaviour because not enough of them wanted to form the stock in the lab. Once placed back in the wild, without enough cells to form the stalk, the whole community collapsed.