our planet’s rich biodiversity, called ‘speciation’ clearly happens regularly, but scientists couldn’t quite pinpoint the driving forces behind it. for speciation to occur, two branches of the same species must stop breeding with one another for long enough to grow apart genetically. the most obvious way this can happen is through geographical isolation. but geographical isolation is not enough to explain all speciation. clearly, organisms do sometimes speciate even if there is no clear river or mountain separating them. the other mechanism that can theoretically divide a species is ‘reproductive isolation’. this occurs when organisms are not separated physically, but ‘choose’ not to breed with each other thereby causing genetic isolation, which amounts to the same thing. a research team from harvard university, usa, discovered that closely related species of the butterfly genus ‘agrodiaetus’, living in the same geographical space, displayed unusually distinct wing markings. the females are brown while the males exhibit a variety of wing colours ranging from silver and blue to brown. these wing colours apparently evolved as a sort of ‘team strip’, allowing butterflies to easily identify the species of a potential mate. if closely related species are geographically separate, they tend to look quite similar. that is to say, they do not display a distinctive ‘team strip’. if closely related species are living side-by-side, they frequently look strikingly different – their ‘teams’ are clearly advertised. this has the effect of discouraging inter-species mating, thus encouraging genetic isolation and species divergence. ‘for me, this is a big discovery just because the system is very beautiful’ says dr nikolai kandul . this process, called ‘reinforcement’, and prevents closely related species from interbreeding thus driving them further apart genetically and promoting speciation.