AN EXPECTANT silence has descended on the small room in the Royal Netherlands Academy of Arts and Sciences in Amsterdam. , a theoretical biologist from the University of Oxford, is taking his time to set up his presentation. When he鈥檚 ready, he denounces three of his colleagues as 鈥渦nscholarly鈥� and 鈥渢ransparently wrong鈥�, and wonders what could have led such 鈥渢alented, honest biologists鈥� to be so 鈥渕isguided鈥�.
It鈥檚 day one of a , and exchanges are fierce. At stake is one of the pillars of modern evolutionary biology: the theory of inclusive fitness, which explains how altruistic behaviour can spread through a population. Altruism, in this context, refers to any behaviour which helps the chances of survival of others at the expense of the altruistic individual. Honeybees, which sting intruders to protect their hive and sign their own death warrant in the process, are a classic example.
The conference is the latest stage of a over the work of three Harvard University scientists: mathematical biologists and , and social insect guru and father of sociobiology . Last month, they published a paper in Nature attacking inclusive fitness ().
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The details of their attack are technical and mathematical, but the consequences could be far-reaching. They say inclusive fitness is irrelevant to the real world and want to replace it with a series of equations that could describe the evolution of cooperation in far more detail than ever before.
Their statements have infuriated many of their colleagues, including Grafen, who say their approach has just as many problems as inclusive fitness.
The story dates back to 1955, when British geneticist J. B. S. Haldane was asked if he would risk his life to save another. He supposedly replied that he would only do so to save at least two brothers or eight cousins, reasoning that this would preserve enough copies of his genes to justify his own death. This idea 鈥� that animals are more likely to show altruistic behaviour towards individuals they are related to 鈥� is called kin selection.
Haldane鈥檚 colleague William Hamilton later drafted a mathematical description of the phenomenon, known as inclusive fitness, which assigns numerical values to the costs and benefits of an animal鈥檚 actions. In theory, inclusive fitness makes it possible to calculate the extent of the spread of a given altruistic behaviour 鈥� such as staying with your parents to raise your siblings 鈥� through a population. Hamilton鈥檚 maths has been used for decades by biologists studying cooperation in animals and was a major inspiration for 鈥荣 The Selfish Gene.
The problem, say Nowak and Tarnita, is that the calculations just don鈥檛 work in the real world because they rely on a limiting set of conditions that nature does not stick to. For example, they are only valid for interactions between pairs of animals, which is fine for solitary species whose individuals rarely meet, but no use in studying thousands of ants sharing a colony. What鈥檚 more, they do not work for populations that are under strong pressure to evolve.
These and other limitations, Tarnita says, mean that the maths of inclusive fitness is not relevant to the real world. Instead, she says biologists should use the models of population genetics, which focus on interactions between different gene variants. These models avoid the messiness of predicting the consequences of behaviour and don鈥檛 require any dubious assumptions.
Tarnita has shown that by using standard population genetics equations, it is possible to produce an all-encompassing model. In Amsterdam, she excitedly explained that when she plugged Hamilton鈥檚 conditions into her model, its equations simplified to those of inclusive fitness. Hamilton鈥檚 maths, she concludes, describes a special case of a broader model of how all behaviours evolve: it is not wrong, but limited.
鈥淭he new model is all-encompassing, and represents a broader theory about behaviour鈥�
Nowak points out that, in thousands of insect species, daughters leave the nest despite being as closely related to each other as the workers in an ant colony. This suggests there is some factor other than kin selection keeping workers in the nest and driving altruistic behaviour.
Some biologists have embraced the new ideas: of the University of British Columbia in Vancouver, Canada calls them 鈥渁 great step in the right direction鈥�. But according to Grafen and many others, they are nothing new. They say theoretical biologists have always known that inclusive fitness was an approximation, though this seems not to have filtered through to experimental biologists, who have tended to take it as gospel.
鈥淪ome call Tarnita and Nowak鈥檚 model a step in the right direction. To others, it is lunacy鈥�
What鈥檚 more, in order to use Nowak and Tarnita鈥檚 model to study the evolution of a behaviour, you would need to know an enormous amount about the genes involved 鈥� their identity, location and interactions.
鈥淟unacy!鈥� cries Grafen. Even if you knew all of this, he says, it would only illuminate the process for one species. So it would be better to stick with inclusive fitness, rough and ready though it is, because it will enable biologists to make predictions about how various species should behave 鈥� and indeed already has. Many of his peers agree, arguing that inclusive fitness should still be used as a 鈥渞ule of thumb鈥�.
The argument seems set to run and run. As 麻豆传媒 went to press, more than 140 leading biologists, including several who were present in Amsterdam, had signed a letter to Nature criticising Nowak鈥檚 paper 鈥� though the journal would 鈥渘either confirm nor deny鈥� that it had received the letter. Nowak seems to have been taken aback by the fuss, saying: 鈥淚 didn鈥檛 expect our work to be so controversial.鈥�
