Why do some species have thousands of sterile individuals?

We posed this question to Elva Robinson from the University of York...

Elva - In some species of ants, there are workers that are completely sterile although in many species of ants, bees and termites, the workers can actually reproduce a bit, but not as much as the queen. This posed a problem for Darwin when he was thinking about evolution by natural selection because usually, evolution should move individuals towards the best chance of passing on their own genes directly to the next generation. Obviously, sterile worker ants can't do that. But they are, of course, very closely related to the queen who is their mother, and actually, because of ant genetics, they're more closely related genetically to their mother than we are to our own mothers, because ant genetics work slightly differently. So, this means that their genes will be passed on to the next generation through their siblings, through their sisters, the future queens of other colonies, and through the males that that colony produces. Chris - So it's less "selfish gene", it's more that the genes will go on, but you have to be there to help the genes flow from somebody else. But because you're closely related to them doesn't matter? Elva - Yes and we call it kin selection; acting in the interests of the family when it's very closely related. There are also big efficiency benefits for these ant colonies because of the way they organise their division of labour. So they can very efficiently help their siblings to reproduce.