The common understanding of evolution is the survival of the fittest, but can this explain those individuals within a species that display unselfish, altruistic behaviour? Dr Jonathan Birch of the Department of Philosophy offers a framework for organising our explanations of social behaviour in the natural world.
At the end of each day the workers of the Brazilian ant Forelius pusillus seal their nest entrance, leaving them exposed to the cold night-time temperatures. This selfless act is likely to kill them, but the worker-seal increases the survival chances of their sisters who will breed the next generation of ants.
This example of “altruistic” behaviour by insects poses a puzzle for Charles Darwin’s theory of evolution by natural selection. The Victorian biologist proposed that the individuals with characteristics most suited to the environment are more likely to survive and breed successfully, with these characteristics then passed on to the next generation.
Darwin discussed how behaviours sometimes reduce an individual’s chances of survival, offering the example of sterile male bees, in his book On the Origin of Species. A century later, W. D. Hamilton, while doing a PhD at the LSE, developed the theory of “kin selection” to explain this behaviour. In kin selection, close relatives are more likely to share genes. The genes for altruism then spread through the population because the behaviours they produce cause genetic relatives to have more offspring.
Kin selection has been challenged in recent decades by an alternative theory called “group selection”. In this explanation, the altruist and the recipient of their altruism are part of the same stable group. Natural selection operates at the level of whole groups rather than at the level of individuals.
The two theories were once considered rivals by evolutionary biologists, where only one theory could be correct. Nowadays, the picture is more complicated. Dr Jonathan Birch, Associate Professor in LSE's Department of Philosophy, has written an article in Current Biology that argues for a reframing of the debate to build a better understanding of evolutionary processes that take place within populations.
Dr Birch says: “The basic underlying process is that of a gene for altruism spreading because bearers of the gene are clustered together, so that the benefits of the altruism fall on all other bearers of the gene. But that basic process can vary in its degree of ‘kin selection character’ or ‘group selection character’.”
In his article, Dr Birch introduces the idea of the “K-G space”, a tool for thinking about the degree of “kin selection character” and “group selection character” of the evolutionary process.
Dr Birch explains how the “K-G space” could apply to our understanding of human evolution. He gives the example of the biologist E. O. Wilson, who, earlier in his career, wrote that human cooperation evolved through kin selection, but later asserted that civilisation evolved through group selection.
Dr Birch says: “If you think these ideas are simply two ways of looking at the same process, Wilson’s conversion makes no sense. But my framework allows for a more charitable reconstruction of Wilson’s U-turn.
“Wilson used to think close genetic kinship was important: people were mainly altruistic towards their close kin. He’s changed his mind on this, and now thinks early human groups were not composed of close kin at all. Instead, he thinks human cooperation evolved due to fierce intergroup competition between well-defined groups of non-relatives.”
Dr Birch adds we can think of Wilson’s changing perspective as “moving through K-G space, from a hypothetical process with a lot of ‘kin selection character’, and not much ‘group selection character’, to a new hypothetical process with a lot of ‘group selection character’ and not much ‘kin selection character’”.
In this reading, kin and group selection are more like continuous variables rather than sharply distinguished alternatives.
“My framework is intended to help biologists frame the debate in a clearer way, while remaining neutral. When biologists locate their hypotheses in ‘K-G space’, empirical evidence can be used to decide between them.”