Altruism Flashcards
(22 cards)
What is altruism?
Any behavior that increases the fitness of another individual at a cost to the actor
- Surprisingly common
How does altruism evolve?
Only evolves if helping leaves more copies of the “helping” allele than if the individual did not help.
- Your relatives are the individuals who are most likely to share your alleles!
Between parents and offspring, relatedness is always ___%.
50 (0.5)
What is r between grandparents and grand offspring?
0.25
Just a friendly reminder, what are the probability rules?
1) If both things have to happen (AND) - multiply!
2) If either thing could happen (OR) - add!
How do we determine how likely individuals can have the helping allele?
Hamilton’s rule!!
What is Hamilton’s Rule?
For altruism to evolve, the benefit (B) obtained by the recipient must be greater than the cost to the altruist (C), adjusted for the degree of relatedness (r) between the individuals.
- r*B - C has to be greater than 0 for altruism to evolve.
What is cooperative breeding?
A social system in which individuals contribute to the reproduction of others at the expense of their own reproduction.
Under what conditions might rB > C?
1) High benefit to helping can be directed towards close relatives (rB large)
2) Likelihood of reproducing on your own is small (C small)
How do individuals direct their altruism towards relatives?
1) Your relatives are around you (based on population structure).
2) Individuals might learn who their relatives are based on their early experience (learning).
3) There are others, such as cues of early shared environment and recognizing similarity to self.
What’s another way of directing their altruism towards relatives?
The greenbeard gene
What is the greenbeard gene?
Encodes both a helping behavior and a recognition of that same phenotype.
- It also allows individuals to direct help towards others who definitely share the helping allele (because they have that same sharing phenotype).
- “If you are only helping individuals with green beards, you know those green-bearded individuals have the helping allele. So, you can be sure that, for that locus (gene), you are helping individuals who definitely share your alleles.
What is eusociality?
An extreme form of altruism in which some individuals forgo all reproduction.
What is the haplodiploid genetic system?
In this species, the females are diploid (2 copies of chromosomes) but the males are haploid (1 copy of chromosomes). Females develop from a combination of egg and sperm into a diploid zygote and become queens or workers. The queen can also lay unfertilized eggs; in them, they just develop directly as haploid males. Since males are haploid, there is no recombination or independent assortment, therefore, every sperm is identical.
- This means the value of relatedness changes because of the males being haploid!
How can eusociality evolve?
Eusociality can evolve because females are more related to their sisters than they would be to their own offspring.
How do we get the evolution of altruism among unrelated individuals?
Altruism between unrelated individuals can evolve via direct reciprocal altruism.
- We think this is why because, over time, the behavior doesn’t come with a cost because the help is reciprocated! As long as the benefit of helping is greater than the cost of helping.
What does reciprocal altruism require in order to evolve?
1) Net fitness benefit received > net cost of helping
2) Individual recognition
3) Repeated interactions with the same partner
Cheating makes the evolution of reciprocal altruism unlikely. How can we explain it?
Back to the prisoner’s dilemma! Do you rat out your partner in exchange for a pardon?
What is the tit-for-tat strategy? What would happen if everyone in the population used this strategy?
- Cooperate at first; then repeat what your partner did in the previous round.
- If everybody in the population is using this strategy, then everybody is just going to keep cooperating. So, we get this evolution of reciprocal altruism.
Altruism between unrelated individuals can also evolve via ____________ __________________.
Indirect reciprocity
Describe indirect reciprocity.
- Individual A helps individual B. Individual C sees this interaction.
- After C observes this helping behavior, C is more likely to help A than an individual they did not observe being altruistic. This is indirect reciprocity.
- This requires keeping track of others’ reputations for helping (image score). Because of this, indirect reciprocity is rare.
What is an image score?
Each individual’s reputation/past history of engaging in this helping behavior.
