Cheetahs have two problems: their numbers are low because their habitats have disappeared over time, and they have very low genetic diversity. Neither factor bodes well for their future, but which presents them with the greatest risk of extinction? This isn’t just an academic question. It’s one with real consequences for conservation, and affects whether breeding programmes should just focus on raising more cheetahs, or should carefully mix and match parents to produce genetically diverse young.

Really, what you want is an experiment that tinkers with population size and genetic diversity independently to see which matters most. And obviously, you cannot do that with cheetahs since they are rare and hard to work with.  And, you know, endangered.

Tim Wootton from the