More work has been done on to date on possible levels of selection higher than the individual.
Units of selection above the individual
family
social groups
populations (includes maintenance of sexual reproduction theories)
species (punctuated equilibrium)
Most incidences of selection above the individual involve family selection, formally defined as kin selection.
The concept of inclusive fitness and kin selection were developed together.
Haldane remarks in a pub that he would sacrifice himself for relatives. Asked how many relatives were enough he answered "I am willing to die for two brothers, four uncles or eight cousins".
He is referring to Hamilton's theory of inclusive fitness and the coefficient of relatedness.
INCLUSIVE FITNESS (Hamilton): consists of two components.
(1) Direct fitness: personal reproduction
(2) Indirect fitness: additional reproduction through relatives because of shared genes.
The coefficient of relatedness dictates on average how many genes relatives should share in common. For example a half sib or recipient(r) inherits 1/2 of their genes from the same parent. So does the actor(a). So the probability they will share the same genes from that parent on average is 1/4 or 1/2 multiplied by 1/2. View the diagram below and see if you can see how the coefficient of relatedness is determined in every case.
p=parent, a=actor, R=recipient of behavior, r=coefficient of relatedness.
(Note: The coefficient is an average, based on your probability of inheriting the same "grandparent chromosomes" from your parents. You can be very very similar to sibs in this regard or very different, as in this diagram.)
HAMILTON'S RULE
If Benefit (coefficient of relatedness) - cost > 0, gene for helping will spread. Now can you explain Haldane's remarks?
Does Hamiltons rule explain the evolution of larger groups?
Developed by Hamilton to explain the evolution of social insects. Most altruistic of all societies known, are those of social insects. Colonies consist of sisters and sex determination is haploid-diploid system. Males are haploid; females develop from fertilized eggs and are diploid. So daughters (2n) from a founding queen share 50% of their genes from their mother and 100 % of all genes from their father. Their r is 3/4 if mom mates with a single male, with 1/2 of c being assured and 1/4 an average probability that they inherited similar genes from Mom. So sisters who sacrifice their own reproduction and feed developing queens, share an extraordinary amount of genes with those of developing queens, if they were sired by the same father.
Homework papers to examine. These should give you a better idea if you understand inclusive fitness and kin selection.
bee eater paper.
naked mole rats
An interesting aside
How do individual assess relatedness?
In vertebrates it has been suggested the major histocompatibility gene complex plays a role. This is a matching system used by the immune system to tell self from non-self. In mice different genotypes correlate with urine odor and individuals could recognize full sibs from 1/2 sibs. Mice will nest communally and mothers, whose nests were removed, placed their young in other nests containing offspring with similar MHC genotypes.
In Humans?
Hamilton's theory is now considered the default for explaining altruistic behavior in groups where individuals are related.
This theory has become the null hypothesis whenever see altruistic behavior. Example: ducks
Even when groups are related, be on the lookout for selfish behavior.
But are all groups formed of related individuals?
a. Selfish herds (ravens, frogs, zebra, antelope)
What is the benefit to being with a group of unrelated individuals.
The argument.
Consider two frog ponds. One has two frogs, the other 10. When a predator arrives what are the chances an individual in each pond will be taken?
Additional benefits to a large group: The greater number of eyes watching for predators.
Additional costs?
b. In groups often find behavior that could be considered altruism. Sentinel behavior is common.
Example: Tail raising in deer
was once thought to be altruistic because as soon as one deer raises its tail, all flee. However, researchers have pointed out it is always a deer far away from a predator that raises its tail, and a predator never chases a deer that has raised its tail.
So is the deer talking to other deer?
Watch out, there is a predator about.
Or is the deer talking to the potential predator?
Don't chase me, I see you and I know what direction to run in. Chase someone who you are near and hasn't noticed you yet.
What evidence would you have to collect to show that this was altruistic behavior?
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What about unrelated group selection (no kin selection involved) versus individual selection?
First postulated by Wynne-Edwards to explain lack of reproduction potential in certain species.
Group selection is shown to be experimentally possible.
For example, Wade allowed beetle colonies to breed for 37 days. He then set up new colonies from individuals in high and low fecundity colonies each consisting of 16 individuals. He could over time produce colonies of low fecundity, showing that group selection outweigh individual selection in low fecundity colonies.
Group selection then is possible, but rate of group extinction has to be high and migration of selfish genes into altruistic colonies low.
Group selection was modeled by Maynard Smith. He models patches of altruists and selfish individuals, also empty patches. Emigration of selfish individuals destroys altruists unless extinction of selfish colonies is very high.
This translates into a short generation time for selfish groups to be able to "win," such as those created by Wade. An adult beetle can survive for months and so the generation time for groups in Wade's experiments were very short compared to an adult beetle's normal life span.
The problem is where one would find this conditions for groups, i.e. short generations (less than or equal to an individual life span) or high extinction rate. and low migration.
In most cases, individual selection is thought to swap out group selection since these conditions are not met in most natural situations.
However, there is a theory that these conditions are met if virulence is high and chances of catching a pathogen/parasite is high. But more on that when your tackle theories on the maintenance of sexual reproduction.
Reciprocal altruism is rare but the only other explanation to date for altruistic behavior above the individual level, other than kin selection.
Whether it is a good explanation rests on the
cost to the altruist
and whether
" cheaters can be recognized" (Why? Think about problems with group selection.)
and there is opportunity for repeated interaction.
- Vampire bats and humans. This is a long paper, those of you responsible for answering the questions may want to skim it first and then hunt for relative information.