G. S. Wilkinson

G. S. Wilkinson is the researcher whose field observations and captive-bat experiment give empirical weight to the book’s account of reciprocal cooperation. By documenting food-sharing between unrelated vampire bats and testing whether they distinguish familiar roostmates from strangers, Wilkinson helps show how repeated interaction and individual recognition can sustain assistance beyond genetic kinship.

Research on Vampire Bat Sharing

Wilkinson’s work enters the discussion through an ordinary but uneven predicament: vampire bats feed at night, and finding a meal is difficult. A bat that succeeds may take in more blood than it needs immediately, while another may return to the roost without having fed. On a later night, their fortunes may reverse. Wilkinson observed that bats that had found food sometimes donated blood by regurgitation to less fortunate companions, a pattern that made reciprocal assistance a candidate explanation.

The observations did not reduce sharing to a single cause. Of 110 regurgitations Wilkinson witnessed, 77 could readily be understood as mothers feeding their young; many other instances involved genetic relatives. But some donations occurred between unrelated bats, for which kinship alone could not account. These unrelated bats tended to be frequent roostmates, a circumstance that gave them repeated opportunities to encounter one another and potentially exchange help over time.

The Costs and Benefits of Donation

To assess whether the sharing could fit the logic of a Prisoner’s Dilemma, Wilkinson examined how quickly starving bats lost weight. From those rates he estimated how long a well-fed bat, an empty bat, and bats at intermediate levels of starvation would take to die. He then expressed the value of blood in hours of prolonged life, allowing the costs and benefits of a donation to be compared in terms of survival.

The value of a given amount of blood depended on the recipient’s condition: it added more time to the life of a highly starved bat than to that of a less starved one. Consequently, the donor’s increased risk from giving blood could be small compared with the recipient’s increased chance of surviving. The same quantity of blood was less valuable to a donor who had fed successfully than to an unlucky companion that urgently needed it. Yet a well-fed donor could still benefit from refusing to share if it could avoid a later repayment; that possibility makes retaliation and reciprocal response relevant to the proposed model.

Testing Recognition and Familiarity

A further condition for repeated reciprocity is that bats can distinguish one another as individuals. Wilkinson tested this with captive bats drawn from two separate groups taken from caves many miles apart. He removed one bat for a night and starved it while the others were fed, then returned it to the roost and watched to see which bats would provide food. The procedure was repeated many times, with different bats taking turns as the deprived individual.

The origins of the captive bats made the outcome informative: a donor from the same original cave could be treated as an old associate, while a bat from the other cave was a newcomer. Across thirteen observed donations, twelve came from an old associate of the starved bat and only one from a newcomer. The account calculates that such a division would arise by chance with odds of less than one in 500, and takes the result as strong evidence that bats were biased toward helping familiar companions rather than strangers.

Significance and Limits

Together, the observations and experiment support a specific, measured conclusion. Vampire bats’ food-sharing includes both kin-directed care and donations between unrelated roostmates; the latter occur in a social setting where repeated encounters are possible, and the captive test indicates preferential help for familiar individuals. Wilkinson’s work therefore supplies evidence for a route by which assistance can persist without close genetic relationship, provided individuals meet again and can respond to past interactions.

The findings are presented as a case that appears to fit the conditions of reciprocal cooperation, not as a claim that every donation has the same motive or that the model explains every feature of bat social life. The account contrasts the familiar image of vampires as symbols of predation with observations of sharing and lasting ties among bats. Wilkinson’s contribution is central to that contrast: by testing behavior rather than relying on myth, his research makes cooperation among unrelated animals a concrete possibility within an evolutionary account of selfish genes.