    10

    T he leopard, thrown off track by the commotion, eventually gives up

    and walks away.23

    The Thompson's gazelle is not alone.  Social animals of all

    kinds--mammals and birds alike--shriek, thump or jump to warn their

    companions of an impending attack.  Every one of the shriekers takes

    the chance that his or her warning gesture will make her the first victim

    of the hunter's assault.

    The theory of kin-selection says the jumping or thumping animal

    is protecting her relatives.  In a small number of cases, this hypothesis

    has worked out brilliantly.  But in many others, it's been a failure.

    Large groups of animals do not just consist of brothers, sisters and

    cousins.  In fact, mobs like the flocks of birds that migrate thousands of

    miles each spring and fall seem to contain very few close relatives at

    all.24  Yet members of the flock still shriek a warning when a hungry

    raider approaches.  Why do these creatures choose to make themselves

    conspicuous?

    A stealthy meat eater will have an easy time creeping up on a

    group whose members dare not act as lookouts for their neighbors.

    That social band's days on the savannah are numbered.  But the

    aggregation whose participants court destruction by shrieking-up is

    primed for self defense. An occasional individual may suffer, but the

    group will live to face another day.25

    Individual selectionists have made a heroic effort to deal with the

    problem of altruism via the concept of kin selection.  But there is a

    more subtle challenge to the primacy of personal survival they haven't

    yet dared tackle: intropunitive behavior.  In the 1950's, psychologist

    Harry Harlow at the University of Wisconsin wanted to see how

    necessary the love of a mother and friends were to humans.  He

    couldn't wrench newborn babies from their mamas' arms and raise

    them in isolation cages.  But he could do the next best thing.  He tried

    the experiment on newborn monkeys.  The simians raised without

    social contact frequently sat in a corner of their cage, curled into a ball,

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