What comes next for evolution? This seems like a simple question. Every day we are learning more about the history of life on earth, and we would expect that, over 150 years since Charles Darwin published On the Origin of Species, the life of the past could be used to extrapolate the trajectory of evolution’s arrow. Regarding our own species, especially, there is a pervasive desire to know what our distant descendants might be like.

But this question is flawed. Even though there are evolutionary constraints – not everything we can imagine is possible – life is not following a tightly-restricted road of progress towards a pre-determined goal. Natural selection,