38. For an individual A to help his relative B or C, the fitness benefits and costs are 50 and 20 units, respectively. However, following Hamilton’s Rule, A should help B only but not C. How are B and C genetically related to A?
(1) B-Son, C-Nephew (2) B- Son, C-Brother
(3) B- Sister, C- Nephew (4) B- Father, C-Mother
Step 1: Calculate the Relatedness Threshold
Hamilton’s rule states that A should help if:
r×50>20 ⟹ r>2050=0.4
A should help a relative only if their genetic relatedness is greater than 0.4.
Step 2: Genetic Relatedness of Family Members
Standard coefficients of relatedness:
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Son (parent-offspring): r = 0.5
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Brother or Sister (full sibling): r = 0.5
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Nephew or Niece: r = 0.25
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Cousin: r = 0.125
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Uncle/Aunt: r = 0.25
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Father/Mother: r = 0.5
These values are widely accepted in genetics and kin selection theory.
Step 3: Apply the Threshold
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B as Son: r = 0.5 (> 0.4) — A should help B.
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C as Nephew: r = 0.25 (< 0.4) — A should NOT help C.
Similarly, if C were a brother (r = 0.5), A would help; if C were a cousin (r = 0.125), A would not help.
Step 4: Match to the Options
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Option 1: B-Son, C-Nephew — matches the calculation.
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Option 2: B-Son, C-Brother — both would be helped, but the question says only B should be helped.
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Option 3: B-Sister, C-Nephew — sister would be helped, but the question says only B should be helped.
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Option 4: B-Father, C-Mother — both would be helped, as both have r = 0.5.
Conclusion
According to Hamilton’s rule, A should help B (his son, r = 0.5) but not C (his nephew, r = 0.25), because only the son meets the relatedness threshold required for the altruistic act to be favored by natural selection.
Correct answer: (1) B-Son, C-Nephew
1 Comment
Kajal
October 15, 2025Option 1 is correct