At that point I came across a remarkable paper by an Israeli biologist, Amotz Zahavi, who had conceived a novel general theory about the role of costly or self-destructive signals in animal behaviour. For example, Zahavi attempted to explain how deleterious male traits might attract a female precisely because they constitute handicaps. On reflection, I decided that Zahavi's hypothesis might apply to the birds of paradise I studied. Suddenly I realized, with growing excitement, that his theory perhaps could also be extended to explain the paradox of our use of toxic chemicals, and our touting it in advertisements.
Zahavi's theory as he proposed it concerned the broad problem of animal communication. All animals need to devise quick, easily understood signals for conveying messages to their mates, potential mates, offspring, parents, rivals, and would-be predators. For example, consider a gazelle that notices a lion stalking it. It would be in the gazelle's interests to give a signal that the lion would interpret to mean, 'I am a superior, fast gazelle! You'll never succeed in catching me, so don't waste your time and energy on trying. Even if that gazelle really is able to outrun a lion, giving a signal that dissuades the lion from trying would save time and energy for the gazelle too. But what signal will unequivocally tell the lion that it is hopeless? The gazelle cannot take the time to run a demonstration 100-yard dash in front of every lion that shows up. Perhaps gazelles could agree on some quick arbitrary signal that lions learn to understand, such as that pawing the ground with the left hind foot means 'I claim that I'm fast! However, such a purely arbitrary signal opens the door to cheating; any gazelle can easily give the signal regardless of its speed. Lions will then catch on that many slow gazelles giving the signal are lying, and lions will learn to ignore the signal. It is in the interests both of lions and of fast gazelles that the signal be believable. What type of signal could convince a lion of the gazelle's honesty? The same dilemma arises in the problem of sexual selection and mate choice that I discussed in Chapters Five, Six, and Nine. This is especially a problem of how females pick males, since females invest more in reproduction, have more to lose, and have to be choosier. Ideally, a female should pick a male for his good genes to pass on to her offspring. Since genes themselves are hard to assess, a female should look for quick indicators of good genes in a male, and a superior male should provide such indicators. In practice, male traits such as plumage, songs, and displays usually serve as indicators. Why do males 'choose' to advertise with those particular indicators, why should females trust a male's honesty and find those indicators attractive, and why do they imply good genes?
I have described the problem as if a gazelle or courting male voluntarily picks out some indicator from among many possible ones, and as if a lion or a female decides on reflection whether it is really a valid indicator of speed or good genes. In practice, of course, those 'choices' are the result °f evolution and become specified by genes. Those females who select males on the basis of indicators that really denote good male genes, and those males that use unambiguous indicators of good genes for self-advertisement, tend to leave the most offspring, as do those gazelles and lions that spare themselves unnecessary chases. As it turns out, many of the advertising signals evolved by animals pose a paradox similar to that posed by cigarette advertisements. The indicators often seem to be ones that do not suggest speed or good genes but instead constitute handicaps, expenses, or sources of risk. For example, a gazelle's signal to a lion that it sees approaching consists of a peculiar form of behaviour termed 'slotting'. Instead of running away as fast as possible, the gazelle runs slowly while repeatedly jumping high into the air with stiff-legged leaps. Why on earth should the gazelle indulge in this seemingly self-destructive display, which wastes time and energy and gives the lion a chance to catch up? Or think of the males of many animal species which sport large structures, such as a peacock's tail or a bird of paradise's plumes, that make movement difficult. Males of many more species have bright colours, loud songs, or conspicuous displays that attract predators. Why should a male advertise such an impediment, and why should a female like it? These paradoxes remain an important unsolved problem in animal behaviour today.
Zahavi's theory, which remains controversial among biologists, goes to the heart of this paradox. According to his theory, those deleterious structures and forms of behaviour constitute valid indicators that the signalling animal is being honest in its claim of superiority, precisely because those traits themselves impose handicaps. A signal that entails no cost lends itself to cheating, since even a slow or inferior animal can afford to give the signal. Only costly or deleterious signals are guarantees of honesty. For example, a slow gazelle that slotted at an approaching lion would seal its fate, whereas a fast gazelle could still outrun the lion after slotting. By slotting, the gazelle boasts lo the lion, 'I'm so fasl that I can escape you even after giving you this head slarl. The lion ihereby has grounds for believing in ihe gazelle's honesty, and both ihe lion and ihe gazelle profit by nol wasling lime and energy on a chase whose outcome is cerlain. Similarly, as applied lo males displaying towards females, Zahavi's iheory reasons lhal any male lhal has managed lo survive despite ihe handicap of a big lail or conspicuous song musl have terrific genes in other respects. He has proved thai he musl be especially good al escaping predalors, finding food, and resisling disease. The bigger ihe handicap, ihe more rigorous ihe lest lhal he has passed. The female who selects such a male is like the medieval damsel testing her knighl suilors by walching ihem slay dragons. When she sees a one-armed knighl who can slill slay a dragon, she knows lhal she has finally found a knighl wilh greal genes. Thai knighl, by flaunting his handicap, is aclually flaunting his superiority.
Il seems lo me lhal Zahavi's iheory applies to much cosily or dangerous human behaviour aimed at achieving stalus in general or al sexual benefils in particular. For inslance, men who woo women wilh cosily gifts and olher displays of weallh are in effecl saying, 'I have plenty of money lo support you and children, and you can believe my boast because you see how much money I'm spending now withoul blanching. People who show off expensive jewels, sports cars, or works of art gain slalus because ihe signal cannol be faked; everyone else knows whal those oslentatious objecls cosl. American Indians of ihe Pacific Norlh-wesl used lo seek slalus by competing lo give away as much weallh as possible in ceremonies known as pollalch riluals. In ihe days before modern medicine, lallooing was not only painful bul dangerous because of ihe risk of infection; hence lallooed people in effecl were advertising two facels of iheir slrenglh, resistance lo disease plus tolerance of pain. Men on ihe Pacific island of Malekula show off by the insanely dangerous practice of building a high tower and jumping off it head first, after lying one end of some sloul vines lo iheir ankles and ihe olher end lo ihe lop of the tower. The length of ihe vines is calculaled to slop ihe braggart's plunge while his head is still a few feel above ihe ground. Survival guaranlees lhal ihe jumper is courageous, carefully calculating, and a good builder. Zahavi's iheory can also be exlended lo human abuse of chemicals. Especially in adolescence and early adullhood, ihe age when drug abuse is mosl likely lo begin, we are devoting much energy to asserting our stalus. I suggesl lhal we share ihe same unconscious inslincl lhal leads birds lo indulge in dangerous displays. Ten ihousand years ago, we 'displayed' by challenging a lion or a Iribal enemy. Today, we do it in olher ways, such as by fast driving or by consuming dangerous drugs.