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How does kin selection explain altruistic behavior in social insects?

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Marble bust of Aristotle with a beard and draped robe, showing detailed facial features and wavy hair, set against a dark background. — Philosophy of biology Detail of a Roman copy (2nd century bce) of a Greek alabaster portrait bust of Aristotle, c. 325 bce; in the collection of the Roman National Museum.

Kin selection explains altruistic behavior in social insects—such as ants, bees, and wasps—by demonstrating that individuals can increase their inclusive fitness by helping relatives survive and reproduce, rather than by reproducing themselves.123

This behavior is often analyzed through Hamilton’s rule, expressed as:
$r \times B > C$
where r is the genetic relatedness, B is the benefit to the recipient, and C is the cost to the altruist.4

In many Hymenoptera, a genetic system called haplodiploidy results in sisters sharing 75 percent of their genes, which is higher than the 50 percent they would share with their own offspring. Consequently, a worker insect transmits her genes more effectively by helping the queen produce more sisters than by producing her own progeny. While haplodiploidy may be a predisposing factor, modern research suggests that extreme sociality is also driven by ecological constraints, such as high predation or limited nesting sites, which make staying in the colony and assisting kin a more viable strategy for genetic success than independent reproduction.13