The Meme Machine

150 THE MEME MACHINE
times in the hope of help in bad times. Research has revealed that many animals
do just this, but there is a catch. If you are going to pay back favours, and avoid
being cheated, you must be able to recognise other individuals. Most animals
cannot do this, but many primates can – as can elephants, dolphins, and even
such unlikely species as vampire bats. Vampire bats have a special problem in
that they are very small and can easily die if they go without a meal of blood for
more than two nights in a row. Fortunately, blood meals can be much bigger
than one bat really needs. So the answer is to share your blood – and keep a
track on who owes what to whom.
Gratitude, friendship, sympathy, trust, indignation, and feelings of guilt and
revenge have all been attributed to reciprocal altruism, as has moralistic
aggression, or our tendency to get upset over unfairness. If we have evolved to
share resources with other humans, but to make sure our genes benefit, then our
feelings are the way evolution has equipped us to do it. On this theory not only
moral sentiments, but ideas of justice and legal systems can be traced to the
evolution of reciprocal altruism (Matt Ridley 1996; Wagstaff 1998; Wright
1994).
Game theory has made it possible to explore how and why various strategies
might evolve. Trivers used a game called the Prisoner’s Dilemma in which two
people are kept apart and told they are accused of a crime with a penalty of, say,
ten years in prison. If both stay silent they can be convicted only on a lesser
charge and both get a shorter sentence, say three years, but if one gives evidence
against the other the defector gets off free. What should they do? Obviously the
best outcome all round is for both to stay silent – but there is a strong temptation
to defect – and what if the other one is tempted? – you might as well be tempted
too. There are many other versions using points, money, or other resources.
The important point is that a perfectly rational and selfish person will always
gain by defecting. So how does cooperative behaviour ever come about?
The answer is that in a one-off game it never should, but life is not a one-off
game. We meet people again, and form judgements about their trustworthiness.
The answer to the Prisoner’s Dilemma lies in repetition. In iterated Prisoner’s
Dilemmas people assess the other’s likely behaviour and then both can gain by
cooperating. Players who have not met before often copy each other,
cooperating with cooperators and not with defectors. Persistent detectors are
shunned, and so lose their chance of exploiting others.
Games like this are also used by economists, mathematicians and computer
modellers. In 1979, the American political scientist Robert Axelrod set up a