When Martin Nowak was in high school, his parents thought he would be a nice boy and become a doctor. But when he left for the University of Vienna, he abandoned medicine for something called biochemistry. As far as his parents could tell, it had something to do with yeast and fermenting. They became a little worried. When their son entered graduate school, they became even more worried. He announced that he was now studying games.
In the end, Nowak turned out all right. He is now the director of the Program for Evolutionary Dynamics at Harvard. The games were actually versatile mathematical models that Nowak could use to make important discoveries in fields as varied as economics and cancer biology.
"Martin has a passion for taking informal ideas that people like me find theoretically important and framing them as mathematical models," said Steven Pinker, a Harvard linguist who is collaborating with Nowak to study the evolution of language. "He allows our intuitions about what leads to what to be put to a test."
On the surface, Nowak's many projects may seem randomly scattered across the sciences. But there is an underlying theme to his work. He wants to understand one of the most puzzling yet fundamental features of life: cooperation.
When biologists speak of cooperation, they speak more broadly than the rest of us. Cooperation is what happens when someone or something gets a benefit because someone or something else pays a cost. The benefit can take many forms, like money or reproductive success. A friend takes off work to pick you up from the hospital. A sterile worker bee tends to eggs in a hive. Even the cells in the human body cooperate. Rather than reproducing as fast as it can, each cell respects the needs of the body, helping to form the heart, the lungs or other vital organs. Even the genes in a genome cooperate, to bring an organism to life.
In recent papers, Nowak has argued that cooperation is one of the three basic principles of evolution. The other two are mutation and selection. On their own, mutation and selection can transform a species, giving rise to new traits like limbs and eyes. But cooperation is essential for life to evolve to a new level of organization. Single-celled protozoa had to cooperate to give rise to the first multicellular animals. Humans had to cooperate for complex societies to emerge.
"We see this principle everywhere in evolution where interesting things are happening," Nowak said.
While cooperation may be central to evolution, however, it poses questions that are not easy to answer. How can competing individuals start to cooperate for the greater good? And how do they continue to cooperate in the face of exploitation? To answer these questions, Nowak plays games.
His games are the intellectual descendants of a puzzle known as the Prisoner's Dilemma. Imagine two prisoners are separately offered the same deal: if one of them testifies and the other doesn't talk, the talker will go free and the holdout will go to jail for 10 years. If both refuse to talk, the prosecutor will only be able to put them in jail for six months. If each prisoner rats out the other, they will both get five-year sentences. Not knowing what the other prisoner will do, how should each one act?
The way the Prisoner's Dilemma pits cooperation against defection distills an important feature of evolution. In any encounter between two members of the same species, each one may cooperate or defect. Certain species of bacteria, for example, spray out enzymes that break down food, which all the bacteria can then suck up. It costs energy to make these enzymes. If one of the microbes stops cooperating and does not make the enzymes, it can still enjoy the meal. It can gain a potential reproductive edge over bacteria that cooperate.