Kin Selection, Relatedness and When Helping Pays · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

When helping family pays

Science · Ecology & Conservation · ages 20-22
Name ______________________   Date ____________

  1. What does a relatedness of one quarter mean?

    • A one in four chance of sharing a gene copy from the same ancestor
    • One quarter of all behavior is caused by genes
    • The helper keeps one quarter of every benefit

  2. Two full siblings and two cousins need help. Who is more closely related to you?

    • Both pairs equally, since all are family
    • The full siblings, at about one half versus one eighth
    • The cousins, since distant kin matter more

  3. How does help to kin differ from help between strangers?

    • They are identical, since all helping is kin selection
    • Kin help needs no logic, while stranger help needs shared genes
    • Kin help can pay through shared genes, while stranger help needs another return

  4. The weighted benefit is 3 and your cost is 2. Does helping pay?

    • Yes, since 3 beats 2 in the inequality
    • No, since any cost at all forbids helping
    • Only if the sibling later repays you in full

  5. You pay a cost of 2 to give a full sibling a benefit of 6. What is the weighted benefit, 0.5 times 6?

    Answer: ______________

  6. Why do sterile worker bees raise the queen's young instead of breeding?

    • The queen forces every worker to obey her orders
    • The young carry many of their genes, so raising them spreads those genes
    • Workers cannot tell relatives apart from strangers

  7. Helping an unrelated stranger pays through shared genes alone.

    Circle one:   True   False

  8. A helper pays 3 to give a cousin, relatedness one eighth, a benefit of 16. Does helping pay?

    • Yes, since 16 is far larger than 3
    • Yes, since cousins always deserve help
    • No, since one eighth of 16 is 2, which loses to 3
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Answer key

For grown-ups. Fold this page away before handing over the rest.

When helping family pays W1-mt_scVf8G34WI-s1

  1. A one in four chance of sharing a gene copy from the same ancestor · Relatedness is a shared gene probability, as in half siblings. Nothing about behavior percentages.
  2. The full siblings, at about one half versus one eighth · Closer kin share more gene copies. One half beats one eighth every time.
  3. Kin help can pay through shared genes, while stranger help needs another return · Shared genes pay kin help directly. Strangers need returned favors, reputation, or shared interests.
  4. Yes, since 3 beats 2 in the inequality · The rule compares weighted benefit against cost. Three against two favors helping.
  5. 3 · Multiply relatedness by benefit before comparing with cost. The weighted benefit here is 3.
  6. The young carry many of their genes, so raising them spreads those genes · Raising gene laden relatives is reproduction by proxy. Shared genes make the sacrifice profitable.
  7. False · Strangers share no special genes with the helper. Their help needs favors returned or interests shared.
  8. No, since one eighth of 16 is 2, which loses to 3 · Raw benefit misleads; only the weighted value counts. Two against three fails the inequality.
Worksheet · LightMySky