Why one species branches into two is a question that has haunted evolutionary biologists since Darwin.

Given our planet’s rich biodiversity, “speciation” clearly happens regularly, but scientists cannot quite pinpoint the driving forces behind it.

Now, researchers studying a family of butterflies think they have witnessed a subtle process, which could be forcing a wedge between newly formed species.

The team, from Harvard University, US, discovered that closely related species living in the same geographical space displayed unusually distinct wing markings.

These wing colours apparently evolved as a sort of “team strip”, allowing butterflies to easily identify the species of a potential mate.

Although scientists have speculated about this mechanism for years, it has rarely been witnessed in nature.

“The phenomenon of reinforcement is one of the very few mechanisms that has natural selection playing a role in speciation,” said Harvard co-author Nikolai Kandul. “It might be very widespread but it is hard to find good evidence of it.”

By Julianna Kettlewell

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