FOR four billion years natural selection has rewarded self-interest. Those
creatures that are good at looking after their own reproduction have, almost by
definition, thrived at the expense of others. Curiously, however, over the same
period, life has increasingly become a team game. Genes have gathered into
bigger genomes, cells have clubbed together to become bodies, and in some
species bodies have become social, allying themselves with other bodies within a
colony. Thus, today, some of the most successful animals on Earth鈥攈uman
beings, ants and corals鈥攁re highly social, utterly dependent on the
assistance and cooperation of their fellows. If natural selection chooses
egotism, how can this possibly be?
This conundrum is a modern relative of a question that has baffled
philosophers for three thousand years: why do selfish individuals cooperate for
the greater good of society? Put another way, why isn鈥檛 society always destroyed
by 鈥渃heats鈥� who are happy to step on others so long as they get what they want?
Enter evolutionary biology, which has been in ferment since the 1960s. The
insights gained over this period are today yielding answers to both ancient and
modern questions. But biologists cannot claim exclusive rights over this
victory: to carry out their task they have borrowed heavily from disciplines as
varied as economics, genetics and psychology.
The advantages of cooperation are not mysterious. They are in fact easily
summarised in a single phrase: the division of labour. A large genome can
include more specialised genes. A large cell can include more specialised
organelles. A large body can include more specialised organs. A large colony can
include more specialised individuals. A large economy can include more
specialised firms. And paradoxically, narrowing the task of each unit broadens
the ecological niche of the group. As species, after all, ants and humans are
generalists.
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The division of labour in human society is marked. I rely on other people not
only to grow my food, distribute it and sometimes even cook it (in restaurants,
for example), but to make my clothes, my tools, my entertainment, virtually
everything in my life. If I tried to do all these jobs for myself, there simply
would not be enough hours in the day. Yet everybody gets fed, clothed and
entertained. This is the remarkable thing about the division of labour鈥攊t
makes the whole greater than the sum of the parts.
It pays to betray
So the advantages of cooperation are not in doubt. The problem is how to get
there. The division of labour requires individuals to cooperate while natural
selection favours egotists鈥攚ho would never consider relying on each other.
This is where game theory comes into play. There is no neater way of expressing
this paradox than in a game that has become a favourite of economists,
鈥減risoner鈥檚 dilemma鈥�. In this game the rewards of cooperation are there to be
had, but only if the players can eschew the temptations of egotism. It is a
metaphor for the whole of evolutionary history.
Imagine two prisoners, each faced with the choice of giving evidence against
the other and receiving a short sentence in return. The dilemma arises because
if neither defects on the other, the police can convict them only on a lesser
charge and they would both serve a medium term in prison. As a pair, the best
tactic is to stay silent; but as individuals they are better off defecting.
Why so? Forget prisoners and think of it as a simple mathematical game played
by two people for points. If they both cooperate (鈥渟tay silent鈥�) they each get
three points; if they both defect they each get one. But if one defects and the
other tries to cooperate, the cooperator gets nothing and the defector gets five
points. So, if you are playing and your partner defects, you are better off
defecting, too, so as to gain one point rather than none. But if your partner
cooperates you are still better off defecting: you win five instead of three.
Whatever the other person does, it pays you to defect. Yet the other person
argues the same way, so you both defect when you could have had more points if
you had cooperated.
A tropical rainforest exists only because of similar dilemmas. The trees that
grow in them spend most of their energy growing upwards towards the sky, rather
than reproducing. If they could come to a pact with their competitors to respect
a maximum tree height of 3 metres, the trees would be better off from an
evolutionary standpoint, because they could expend more energy on reproduction.
But they cannot.
So our problem is how to find an evolutionary trajectory that leads egotists
into cooperation, yet avoids or solves the prisoner鈥檚 dilemma. Ants, termites
and corals have found such a trajectory. So have the various organs of your
body, because mutinies by liver cells trying to take over the body are rare
events鈥攖hough they do happen, and we call them cancer. So have the genes
within a genome, which act as team players and only occasionally try to break
the rules and strike out on their own. When they do, we know them as viruses or
the parasite-like B chromosomes which reproduce in cells without having any
apparent use to the organism. More significantly, human society has clearly
found the cooperative trajectory, too.
We human beings live in an intensely sophisticated spider鈥檚 web of exchange
that make us intimately dependent on other people. As the 18th-century economist
Adam Smith put it in The Wealth of Nations: 鈥淚n almost every other race
of animals each individual, when it is grown up to maturity, is entirely
independent and in its natural state has occasion for the assistance of no other
living creature. But man has almost constant occasion for the help of his
产谤别迟丑谤别苍.鈥�
Egotism drives society
Smith realised, however, that this mutual helping does not derive from some
wellspring of unstinting benevolence. It is driven by self-interest. The butcher
sells pork and lamb to make his own living, not to help us. We buy his food to
live, not to help him. Yet the end result is that we both benefit from the
exchange, because of the efficiencies introduced by the division of labour.
Egotism, said Smith, drives society. Yet somehow it does so without falling foul
of the prisoner鈥檚 dilemma.
So how does it work? By far the easiest way round the prisoner鈥檚 dilemma is
to ensure that both players are from the same family. Animals are almost
universally nicer to their closest relatives than to distant ones or strangers,
and they are especially nice to their progeny. This evades the dilemma by
turning it into a non-dilemma. Parents do not mind giving unconditionally to
ungrateful children. In fact, parents go out of their way to be taken advantage
of. This is because they share the same genes as the offspring, and when there
is a contest between individual egotism and gene-egotism, gene-egotism wins
every time.
This is, incidentally, why people misrepresent the theory of 鈥渢he selfish
gene鈥� when they argue that it justifies selfishness. The theory holds that
individuals do things not for themselves or for their families, but for the good
of their genes. But this does not condemn us to a selfish world. Rather, it
rescues altruism. In pursuit of genetic selfishness, animals can evolve to
pursue individual selflessness. That is what a woman does as she devotes all her
efforts to her children. She is being genetically selfish but individually
selfless.
William Hamilton of the University of Oxford put forward the idea that
gene-egotism explains cooperation within the family back in the 1960s. His
theory of kin selection argues that animals help their closest relatives in
order to perpetuate the genes they share. Gene-egotism also explains cooperation
within the body. The liver is happy to work itself to death on behalf of the
ovaries because it shares the same genes. And it explains ant colonies, which
are just big families.
Of course families are still open to abuse by outside cheats. The large blue
butterfly and the cuckoo both parasitise family altruism. Large blues fool ants
into caring for their ant-eating larvae, while cuckoos fool warblers into caring
for their chick-killing offspring. But these highly specialised parasites are
rare. In most cases, families are protected from cheats because natural
selection has equipped parents with ways to distinguish their own offspring from
interlopers and to discriminate in their favour. Most bird species will not
tolerate cuckoo chicks in their nests, for example, while worker ants will not
tolerate the presence of workers from other colonies.
Happy families
If kin selection can account for solidarity within families, it cannot
explain human society or the society of genes鈥攖he cooperation between
genes in a genome. Like ant colonies and bodies, these societies have captured
the benefits of divided labour. But they are not just big, happy families. They
include many unrelated individuals.
So why do they still cooperate? The answer favoured by almost all
evolutionary biologists is reciprocity. Reciprocity came to prominence in the
1980s after game theorists led by Robert Axelrod of the University of Michigan
discovered that tournaments of prisoner鈥檚 dilemma games could be easily won by a
simple computer programme called tit-for-tat. By cooperating with cooperators
and retaliating against defectors, tit-for-tat steadily outscores both. Since
then, despite much research into tit-for-tat鈥檚 vulnerabilities, the basic lesson
remains: strategies which repay favours and selfish acts in kind are good at
getting ahead in prisoner鈥檚 dilemma tournaments. At the same time, zoologists
led by Robert Trivers of Rutgers University, New Jersey, noticed the prevalence
in species as diverse as baboons and vampire bats of strategies that seem to
resemble tit-for-tat.
On this foundation was built the theory of reciprocal society鈥攖hat our
societies work because we exchange favours. This enables us to pursue selfish
goals through the means of cooperation, just as Adam Smith argued. However, the
prisoner鈥檚 dilemma is a two-person game. In a world where you only meet your
immediate neighbour, it pays to be nice. But the world is not like that. It is
hard enough to get two players to cooperate: they must be able to police their
contract by being sure of encountering and recognising each other again. How
much harder is it among three individuals or more?
In 1992, Rob Boyd of the University of California, Los Angeles, argued that
not only tit-for-tat but any reciprocal strategy is incapable of explaining
cooperation in large groups. This is because a successful strategy in a large
group must be highly intolerant of even rare defection, or else freeloaders will
spread rapidly. But the very feature that makes a strategy intolerant of
defection鈥攕uspiciousness鈥攊s the one that makes it difficult for
reciprocators to get together in the first place.
A possible answer to this puzzle lies in a new twist to the prisoner鈥檚
dilemma鈥攕ocial ostracism. If people recognise defectors, they can simply
refuse to play with them. Three years ago, at the University of California, San
Diego, the philosopher Philip Kitcher designed an 鈥渙ptional prisoner鈥檚 dilemma鈥�
game. He populated a computer with four kinds of strategist: discriminating
altruists, who play only with those who have never defected on them
before鈥攁nd then cooperate with them; willing defectors, who always defect;
solitaires, who always opt out of any encounter; and selective defectors who are
prepared to play with those who have never defected before鈥攂ut then,
treacherously, defect on them.
Discriminating altruists easily invade a population of solitaires, because
they find and play with each other. But surprisingly, selective defectors cannot
then invade a population of discriminating altruists, whereas discriminating
altruists can invade one of selective defectors. In other words, discriminating
altruism, which is just as 鈥渘ice鈥� as tit-for-tat, can reinvade antisocial
populations. Its success hints at the power of ostracism as a way of solving
prisoner鈥檚 dilemmas.
Spot the defector
Kitcher鈥檚 programs rely entirely on the past behaviour of partners to judge
whether they could be trusted. But discriminating between potential altruists
need not be so retrospective. It might be possible to recognise and avoid
potential defectors in advance. The economist Robert Frank of Cornell
University, New York, set up an experiment to find out. He put a dozen or so
strangers in a room together for half an hour, and asked them all to predict
privately who would cooperate and who would defect in a single game of
prisoner鈥檚 dilemma. They proved substantially better than chance at doing so. In
just 30 minutes, they could tell enough about others to predict how cooperative
they would be.
We spend much of our lives assessing the trustworthiness of others, and we
make instant judgments with some confidence. Human beings, with their
astonishing ability to recall details of even the most casual acquaintance and
their long lives, are equipped to discriminate against suspected defectors with
far greater aplomb than any other species. Indeed, it might be what is special
about us: we are uniquely good at reciprocal altruism.
Obligation, debt, favour, bargain, contract, exchange, deal鈥攐ur
language and our lives are permeated with ideas of reciprocity. We clearly have
an instinct for social and economic exchange just as we have instincts for
grammatical language and walking upright. The study of that instinct is in its
infancy, but already there are encouraging hints.
Deep in the forest of Ecuador, the Achuar people鈥檚 lives are almost entirely
uncorrupted by modern ideas of exchange, trade and money. Yet when Larry
Sugiyama of the University of California, Santa Barbara, confronted them with
the sorts of tests that reveal our ingrained tendencies to see relationships in
terms of social reciprocity, the Achuar people prove to be just as obsessed with
exchange as traders on the floor of the London futures exchange.
We human beings are the supreme wheeler-dealers of the animal kingdom.
Surprisingly, that may be the reason why we have been able to harness the
division of labour and succeed as a species.