Mates, Kin and Animal Strategies
Explain sexual selection through differences in mating success and examine a hypothetical runaway-selection model. Explore kin selection and inclusive fitness using relatedness and reproductive benefits and costs. Compare hawk and dove strategies using stated toy scores. Study how evidence supports explanations of animal emotion, play and socially learned behaviour.
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Natural selection concerns differences in survival and reproduction. Sexual selection is selection through differences in mating success. Traits can help attract a mate or help an animal compete for access to mates. Peacock displays, bird-of-paradise dances and frog calls can affect mate choice. Such traits may have survival costs, but a cost is not required for sexual selection.
Imagine that longer tails and a preference for longer tails are inherited. Longer-tailed males gain more mates. Across generations, the trait and preference can reinforce each other. This is a runaway-selection model, not proof of how peacock tails evolved. Survival costs and other limits can stop the trend. Tails do not have to grow longer forever.
Genes are inherited instructions. Relatives can share copies through common ancestry. An inherited helping behaviour can spread when helping relatives reproduce benefits shared gene copies enough to outweigh the helper's cost. This is kin selection. Inclusive fitness considers reproductive effects through an animal's own offspring and through relatives, weighted by relatedness. A risky act alone does not establish this explanation.
Worker honeybees usually do not reproduce. A worker stinging a mammal can lose her barbed sting and die. Protecting related hive members can help shared gene copies pass on through their offspring. This does not mean every worker is unable to reproduce or every sting causes death. Meerkat guarding can help relatives, but it can also benefit the guard. Scientists must check the benefits and costs.
In a simplified model, Hamilton's rule is r x B > C. Here r measures relatedness, B is added reproductive success for relatives, and C is lost reproductive success for the helper. Benefit and cost use the same units. With r = 0.5, B = 8 and C = 3, half of 8 is 4. Since 4 > 3, the model predicts that help can be favoured. Real cases need evidence for the values and assumptions.
Game theory models how a behaviour's value depends on others' behaviour. 'Hawk' fights; 'dove' avoids an escalated fight. These name strategies, not species or conscious plans. In a toy model, a resource is worth 4 points and injury costs 8. Two hawks each average (4 - 8) / 2 = -2. A hawk facing a dove gets 4; that dove gets 0. Two doves each average 2. Fighting another hawk lowers the score because injury is costly.
You have studied animal problem-solving. Cognitive ethology studies animal minds, including emotion and play. Scientists compare repeated behaviour, body signals and other explanations. Evidence can support an explanation without proving exactly what an animal feels. Culture involves behaviour learned from others and passed within a group. Scientists distinguish social learning from inherited traits.
Mating success, effects on relatives and interactions with competitors can affect selection. Models need stated assumptions, and explanations of animal minds need evidence.
Lesson, questions and flashcards written for this dataset. Runaway selection, Hamilton's rule calculations and contest scores are presented as stated teaching models.
Readings and flashcard written for this dataset. Linked video: Khan Academy, Animal behavior and offspring success.
More to read
Traits and mating success
Animals differ in their chances of gaining mates. A display can affect a partner's choice, while another trait can help an animal compete for access to mates. Selection through these differences is sexual selection.
The relevant link is mating success. A trait need not harm survival to be sexually selected.
Scientists can use a runaway-selection model to investigate an inherited trait and an inherited preference for it. Under the model's conditions, they can reinforce each other across generations. Costs and other limits can interrupt the trend.
A model describes what could happen under stated assumptions. Observations are needed before using it to explain a real population. It does not establish how a particular display evolved just because that display is large or bright.
When helping relatives affects selection
Relatives can share gene copies through common ancestry. Helping relatives reproduce can therefore affect the success of shared copies. Kin selection explains how such effects can favour an inherited helping behaviour when the benefits, relatedness and costs fit the conditions.
Inclusive fitness considers reproductive effects through an animal's own offspring and through relatives, weighted by relatedness. Strength, speed or a long life alone does not measure it.
Worker honeybees usually do not reproduce. Protecting related hive members can help shared gene copies pass on through those relatives. This does not make every worker unable to reproduce or every sting fatal.
A risky act alone does not identify its evolutionary explanation. Scientists need evidence about who receives help, how closely they are related, and effects on reproduction. They also investigate benefits to the helper itself.
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