even Darwin yearned for a more “top down” approach, so he could conjure up more precise laws to explain a great mass of data. He needed a mathematical model.
The modern understanding of the process of inheritance is now called “Mendelian,” in honor of Gregor Mendel, who had settled for being a monk after failing his botany exams at the University of Vienna. By sorting out the results of crossing round and wrinkly peas, Mendel revealed that inheritance is “particulate” rather than “blending.” Offspring inherit individual instructions (genes) from their parents such that round and wrinkly parents produce either round or wrinkly offspring and not something in between. What is often overlooked in his story is that Mendel was a good student of mathematics. The great geneticist and statistician Sir Ronald Fisher went so far as to call him “a mathematician with an interest in biology.” Mendel uncovered these rules of inheritance because he was motivated by a clear mathematical hypothesis, even to the extent of ignoring ambiguous results that did not fit. Had Mendel conducted an open-minded statistical analysis of his results, he might not have been successful.
A simple equation to show the effect of passing genes down the generations was found in 1908 by G. H. Hardy, a cricket-loving Cambridge mathematician who celebrated the artistry of his subject in his timeless book A Mathematician’s Apology. In an unusual reversal of the usual roles, the work of this pure mathematician was generalized by the German doctor Wilhelm Weinberg to show the incidence of genes in a population. Robert May (now Lord May of Oxford) once went so far as to call the Hardy-Weinberg law biology’s equivalent of Newton’s first law. Thanks to Hardy and Weinberg we now had a mathematical law that applied across a spectrum of living things.
This attempt to model how inheritance works in nature was extended in seminal investigations conducted in the 1920s and 1930s by a remarkable trio. First, Sir Ronald Fisher, whose extraordinary ability to visualize problems came from having to be tutored in mathematics as a child without the aid of paper and pen, due to his poor eyesight. There was also the mighty figure of J. B. S. Haldane, an aristocrat and Marxist who once edited the Daily Worker. I will return to Haldane in chapter 5. The last of this remarkable trio was Sewall Wright, an American geneticist who was fond of philosophy, that relative of mathematics (forgive me for cracking the old joke about the difference: while mathematicians need paper, pencil, and a wastepaper basket, philosophers need only paper and pencil).
Together, this threesome put the fundamental concepts of evolution, selection, and mutation in a mathematical framework for the first time: they blended Darwin’s emphasis on individual animals competing to sire the next generation with Mendel’s studies of how distinct genetic traits are passed down from parent to offspring, a combination now generally referred to as the synthetic view of evolution, the modern synthesis, or neo-Darwinian. With many others, I have also extended these ideas by looking at the Prisoner’s Dilemma in evolving populations to come up with the basic mechanisms that explain how cooperation can thrive in a Darwinian dog-eat-dog world.
Over the years I have explored the Dilemma, using computer models, mathematics, and experiments to reveal how cooperation can evolve and how it is woven into the very fabric of the cosmos. In all there are five mechanisms that lead to cooperation. I will discuss each one of them in the next five chapters and then, in the remainder of the book, show how they offer novel insights into a diverse range of issues, stretching from straightforward feats of molecular cooperation to the many and intricate forms of human cooperation.
I will examine the processes that paved the way to the emergence of the first living things and the extraordinary feats of cooperation that led to multicellular organisms, along with how cellular cooperation can go awry and lead to cancer. I will outline a new theory to account for the tremendous amount of cooperation seen in the advanced social behavior of insects. I will move on to discuss language and how it evolved to be the glue that binds much of human cooperation; the “public goods” game, the biggest challenge to cooperation today; the role of punishment; and then networks, whether of friends or acquaintances, and the extraordinary insights into cooperation that come from studying them. Humans are SuperCooperators. We can draw on all the mechanisms of cooperation that I will discuss in the following pages, thanks in large part to our dazzling powers of language and communication. I also hope to explain why I have come to the conclusion that although human beings are the dominant cooperators on Earth, man has no alternative but to evolve further, with the help of the extraordinary degree of control that we now exert over the modern environment. This next step in our evolution is necessary because we face serious global issues, many of which boil down to a fundamental question of survival. We are now so powerful that we could destroy ourselves. We need to harness the creative power of cooperation in novel ways.
Direct Reciprocity— Tit for Tat
It will have blood; they say, blood will have blood.
—Shakespeare, Macbeth
In the pitch darkness, the creatures take flight. They shun the moonlight, making the most of their sense of smell to track their victims, then land nearby to stalk them. After a quick loping run on all fours they latch on to their prey. Using a heat sensor on the nose, each one can tell where the blood courses closest to the surface of the victim’s skin. Often a meal begins with a quick bite to the neck. There they can hang for up to half an hour, using their long grooved tongues like straws to lap fresh warm blood. Over several nights they return to sup on the same wounds, and it is thought that they are able to recognize the breathing sounds of their victims in the same way as we use the sound of a voice to recognize each other.
What I find most extraordinary of all about vampire bats is what happens when they return to their roost, where hundreds, even thousands of them congregate, suspended upside down. If one member in the roost is unable to find prey during the night’s hunt, its peers will regurgitate some of their bloody fare and share it. The exchange of blood among the bats was first revealed in studies conducted in the early 1980s by Gerald Wilkinson of the University of Maryland. During fieldwork in Costa Rica, Wilkinson found that, on any given night, a few percent of adult bats and one-third of juveniles fail to dine. They rarely starve, however, since well-fed vampire bats disgorge a little precious blood to nourish their hungry peers. What was neat was that his experiments suggested that bats are more likely to share blood with a bat that has previously fed them (the bats spend time grooming each other, paying particular attention to fur around the stomach, enabling them to keep tally).
This is an example of what I call direct reciprocity. By this, I mean simply the principle of give-and-take. When I scratch your back, I expect you to scratch mine in return. The same goes for blood meals among bats. This form of reciprocity is recognized in popular sayings, such as “tit for tat” and the idiom “one good turn deserves another.” The Romans used the phrase quid pro quo—“something for something.” As the vampires suggest, this kind of cooperation dates back long before Romulus and Remus, long before the rise of modern humans.
For direct reciprocity to work, both sides have to be repeatedly in contact so that there is an opportunity to repay one act of kindness with another. They might live in the same road, or village. Perhaps they work together. Or they may encounter each other every Sunday in church. In the case of the bats, they hang about the same cave or hollow. In that way, they can form a “contract” based on helping each other.
The bats are one often cited example of direct reciprocity in nature. Another can be found on coral reefs, where fish of all kinds visit “cleaning stations” where they are scrubbed of parasites by smaller varieties
