Turning the so-called kin selection theory on its head, researchers have said that altruistic behaviour, such as sterile worker ants caring for the offspring of their queen, could evolve through standard natural-selection processes.
Kin selection is based on 'inclusive fitness', the idea that, for example, sterile workers can accrue reproductive benefits by helping their relatives.
In doing so, they help shared genes to survive and get passed on to the next generation. This provides a route for eusociality to evolve.
But Martin Nowak, a mathematical biologist at Harvard University in Cambridge, Massachusetts, and the lead author of the analysis, said:, "there is no need for inclusive fitness to explain eusociality," reports Nature.
Researchers have offered the first mathematical analysis of inclusive fitness theory.
They calculated which of two behaviours, for example defection - such as going off to set up a separate colony - or cooperation would become more prevalent in a population if standard natural selection was at work.
They then worked out what assumptions would be needed for inclusive fitness theory to deliver the same result.
The team discovered that inclusive fitness delivers the same result only in a limited set of specific situations that would rarely hold in reality.
And when the inclusive fitness theory worked, the answer that it provided was mathematically equivalent to that derived from standard natural selection.
"We show that inclusive fitness is not a general theory of evolution as its proponents had claimed. In the limited domain where inclusive fitness theory does work, it is identical to standard natural selection. Hence there is no need for inclusive fitness. It has no explanatory power," said Nowak.
In a second mathematical analysis, the team investigated how eusociality could evolve through standard natural selection.
They found that a gene for eusociality could spread readily as long as the advantages it confers - increasing the lifespan and reproductive success of the queen - kick in even for small colonies.
So colonies that have as few as two or three workers must provide significant advantages to their queen for the gene and the behaviour to become widespread.
"Whether or not eusociality evolves depends on how colony size affects the mortality and fecundity of the queen. Our model also shows that eusociality is hard to evolve but is very stable once it is established," said Nowak.
The study has been published in Nature. (ANI)