If you’ve been reading the news this week, you know that we’ve just been starkly reminded that the Earth is in the midst of a mass extinction – a biodiversity crisis like nothing it has experienced in 65 million years. Yet while species disappear at an unprecedented rate, new species are also being born all around us, and this fascinating process – speciation – is continuing just as it has been for eons. But exactly how does one species become two? This is one of the biggest questions in biology.