• Behaviour for the good of the group has been shown to not be an effective way to describe evolution of behaviour
• For example, the concept of evolving a natural birth control to stop over exploitation of food - this does not appear in nature
• In practice, groups usually do not go extinct fast enough for group selection to be an important force in evolution
• Individual selection is a much more powerful force, since individuals die and are replaced at a faster rate than groups
• Group selection also requires isolated populations where individuals cannot migrate between them to stop selfish individuals from overexploiting the food and spreading their genotype
• Group selection is overall a weak force compared to individual selection

Example: Great Tit nests

(also described in Fitness Proxy)

• Experimental studies show that the optimal clutch size for maximum survival is around 10
  • This would be best for a selfish-gened bird
• but in nature the most common clutch size is 8. WHy?

Hypotheses

Hypothesis A: Lifetime reproductive output

• Perhaps over an individuals entire lifetime, it's better to have slightly smaller clutches which maximize success over an entire life, rather than per breeding attempt.
• Putting more resources into one clutch might reduce the chance of survival to create more clutches in the future

Hypothesis B: Cost of egg production and incubation

• This study placed extra eggs in the nest, but did not account for the work that females do to produce and incubate the eggs.
• If we could somehow force the females experimentally to increase their clutch size we could test this

Summary

Both the original observation and the two hypotheses are measuring Trade-offs:

• Original experiment measured trade-off between offspring number and and quality
• Hypothesis A would examine the trade-off between adult reproductive effort and adult mortality
• Hypothesis B would examine investment in egg production and incubation vs investment in chick care

Dutch Study 2001

This experimental study looked at great tit optimal clutch size in three experimental groups of females in different nest boxes:
a. Free chicks: The females get two extra nestlings added after their brood hatched
b. Free eggs: Two extra eggs are added on the day the female begins incubation
c. Full costs: The female is induced to la two extra eggs by removing the first four eggs on the day they are laid, these are kept nearby and returned when incubation begins.

Results

No difference in amount of young surviving to breeding age was found between the treatments, so no support for Hypothesis B.

However, greater investment in egg survival did have a cost on female survival, which supports Hypothesis A (at least for two eggs).