Genetics play little part in altruistic behaviour
Bee study finds colony, not kin, is the arbiter of cooperation. Andrew Masterson reports.
In what might represent the final nail in the coffin of the controversial evolutionary theory known as “kin selection”, researchers in Japan have discovered that genetics is of little importance in the emergence of altruistic social behaviour in at least one species of insect.
Starting in the 1960s, the idea of “kin selection” was advanced by several scientists – notably the entomologist EO Wilson – to explain altruism among eusocial insects such as ants and bees.
From an evolutionary perspective, altruism – in which an animal sacrifices itself to allow others in its colony to survive – is challenging, because it transgresses the classical idea that the primary function of any individual organism is to pass on its own genes.
Wilson and others initially caused controversy – which later grew into almost-consensus – by suggesting that the operative unit of selection wasn’t the individual but a group of closely related individuals – “kin”, in other words.
Using an elegant equation first constructed in 1964 by evolutionary biologist W.D. Hamilton, Wilson and his colleagues demonstrated that self-sacrificing behaviour could be explained by the idea that the survival of a closely related gene-set was, in evolutionary terms, as valuable as the survival of any individual set.
According to Hamilton’s construct, the survival of an organism’s sister was as useful as the survival of the organism itself, as was the survival of two half-siblings, four cousins, and so on.
Gradually, the idea of kin selection grew in popularity among evolutionary theorists – but not, ironically enough, among Wilson and his inner circle. In a fine example of the scientific method at work, Wilson and his colleagues became concerned that real-world results pointed to an increasing number of exceptions to their neat formulations.
Finally, in a landmark paper published in the journal Nature, he, Martin Nowak and Corina Tarnita formally repudiated the theory, admitting it had “limitations”.
“We argue that standard natural selection theory in the context of precise models of population structure represents a simpler and superior approach, allows the evaluation of multiple competing hypotheses, and provides an exact framework for interpreting empirical observations,” they wrote, prompting uproar among the evolutionary biology establishment, for which kin selection had become part of the orthodoxy.
Now, however, Hokkaido University biologist Eisuke Hasegawa and colleagues have found that among eusocial sweat bees (Lasioglossum baleicum) colony structure is a much more important determinant of success than genetic relatedness.
Sweat bees have two types of nests – large ones in which multiple females work together to tend to a single queen, and smaller ones in which a single mother tends to her own offspring.
Hasegawa and his colleagues studied five populations of sweat bees – each of which contained both types nest – and monitored how often adult females left the nest to forage.
They found that in the larger nests – where cooperation was the name of the game – females foraged more often than those in the smaller nests. What’s more, the smaller nests were left without adult female defenders comparatively often, meaning they were more often subject to predation by ants.
Over all, the researchers calculate that individual females in the cooperative nests had higher levels of fitness – and were thus more likely to be successful in passing on genes – than those in the smaller nests.
Most of this increase, they calculated, was due to the beneficial effects of grouping together. Very little of it could be ascribed to degrees of relatedness.
“There has been a decade-long debate among scientists as to whether genetic similarity or the benefit of grouping is the primary drive of sociality,” says Hasegawa.
“Our study could help reveal some of the factors behind the evolution of cooperation, including among humans, by quantifying how much cooperative behaviour contributes to the increased fitness of altruistic individuals in a group.”
The research is published in the journal Science Advances.