Guillemots

Guillemots are seabirds whose egg-recognition behavior serves as a key example in The Selfish Gene of how selection can favor discrimination over indiscriminate altruism. Because they nest on flat rocks, their eggs may roll away and become mixed with others; recognizing their own speckled eggs enables them to incubate their own rather than rely on communal care that could be exploited.

Nesting and Egg Recognition

Unlike Herring gulls, which do not recognize their own eggs, Guillemots identify theirs by their speckling pattern and actively favor them during incubation. The distinction is linked to their nesting setting: on flat rocks, eggs are liable to roll and become confused with neighboring eggs. Under those conditions, recognizing an individual egg has a direct practical value.

The Communal-Care Thought Experiment

The book considers what would happen if Guillemots instead formed a group-wide babysitting circle in which each adult incubated whichever egg happened to be nearby. Their average clutch is one egg, so such a system would depend on adults reliably sharing incubation rather than increasing their own reproductive output. A bird that laid additional eggs and left others to incubate them could gain an advantage: the more cooperative adults would continue caring for eggs without distinguishing their owners.

Limiting each adult to one egg would not solve the problem if eggs remained unrecognized. Any neglected egg could belong to a cooperative bird just as readily as to a cheater, while the bird laying more eggs could still leave more surviving offspring. The proposed communal arrangement therefore cannot reliably punish the strategy that exploits it.

Discrimination as a Stable Strategy

The book presents active recognition and exclusive incubation as the alternative that defeats the exploitation problem. An indiscriminate cooperative strategy can be invaded by a selfish strategy of laying more eggs and refusing to incubate them; once that cooperation disappears, the exploiting strategy loses the system it depended on. Recognizing and sitting on one’s own egg is described as the Guillemot’s evolutionarily stable strategy: a rival strategy cannot gain an enduring advantage by exploiting indiscriminate care.

The example supports the book’s broader contrast between group-benefit explanations and selection acting through competing strategies. It is not a claim that Guillemots consciously calculate costs, benefits, or fairness. The book uses strategy as a way of describing behavior shaped by selection, and presents the case as an illustration of why apparent cooperation for a group’s benefit need not remain stable when individual reproductive interests diverge.