Evolutionary and comparative perspectives
Introduced| English |
|---|
| inclusive fitness/ɪnˈkluːsɪv ˈfɪtnəs/ |
| fixed action pattern/fɪkst ˈækʃn ˈpætn/ |
A decision before an answer
- A sterile ant works for the colony because her genes are carried by her sisters.
- Your goal: Apply kin selection and inclusive fitness to helping.
Weight help by relatedness
- Kin selection explains helping by inclusive fitness: a gene spreads by aiding relatives who share it. Hamilton's rule says helping pays when rB>C — benefit to the recipient weighted by relatedness exceeds cost to the helper.
- With benefits and costs held equal, closer relatedness makes the inequality more likely to hold: compare siblings (r=.5) with first cousins (r=.125). The rule predicts direction and rough ordering, not exact human behaviour.
Under Hamilton's rule, helping is favoured when:
The benefit must be weighted by relatedness before comparing with the cost.
Release the fixed pattern
- Ethology studies species-typical behaviour.
- A fixed action pattern is an invariant sequence released by a specific sign stimulus and run to completion, as in classic egg-retrieval or mating displays. Because it is triggered rather than assembled, a fixed action pattern can be hijacked by supernormal stimuli — models with exaggerated features.
A bird courts a painted model with an oversized tail while ignoring real mates. The model works as:
Exaggerated features of a releasing cue form a supernormal stimulus hijacking a fixed action pattern.
Test the functional story
- Evolutionary explanations ask about function: how a behaviour raised reproductive success in ancestral environments.
- They compete or combine with learning accounts; prepared learning (fast acquisition of evolutionarily relevant fears like snakes) shows both at once. An evolutionary story is a hypothesis about history, and needs comparative or experimental evidence, not plausibility alone.
Helping a sibling before a cousin fits rB>C ordering. A goose retrieving a doorknob as if it were an egg shows a fixed action pattern released by an exaggerated sign stimulus. Acquiring a fear of snakes after one bad experience, but not of flowers, illustrates prepared learning.
Helping a sibling rather than a cousin follows the ordering predicted by ____ selection.
Inclusive fitness weights aid by relatedness.
Separate the evidence types
- Comparative caution cuts both ways: do not read human motives into animal behaviour (anthropomorphism), and do not assume a human behaviour is learned when cross-species patterns suggest otherwise.
- The examinable skill is matching each explanation to its evidence type.
Treating Hamilton's rule as a precise human calculator, or explaining any observed behaviour as adaptive after the fact; an evolutionary claim needs evidence, not a plausible story.
Which answer fits this case?
Apply kin selection and inclusive fitness to helping
A plausible evolutionary story about a behaviour counts as evidence for it.
Functional accounts are hypotheses about history and need comparative or experimental evidence.
Keep the distinctions
- inclusive fitness 广义适合度 — Reproductive success counting both direct offspring and the reproduction of relatives weighted by relatedness.
- fixed action pattern 固定行为模式 — An invariant species-typical sequence released by a specific sign stimulus.
- Apply kin selection and inclusive fitness to helping.
- Recognise fixed action patterns and sign stimuli in ethology.
- Evaluate evolutionary explanations against learning accounts.
Match each term with its precise meaning in this lesson.
Keep the distinctions stated in the teaching example.
Put this lesson’s reasoning or event sequence in order.
The order follows the stated process; check each stage before the next.