Our study examined a prediction that Darwin made in “On the Origin of Species” but that no-one had tested since Darwin’s time. Further, we find that Darwin’s ideas help us to understand the current conservation crisis.

The diversity of species on Earth increases by a process called speciation – the splitting of one species into two or more (also called “cladogenesis” the genesis of new “clades” or groups of organisms). Darwin proposed that this process happens at different rates in different groups of organisms. He used the analogy of an industrial “manufactory” of goods to explain his idea (“manufactory” was the Victorian word for what we would now call a factory). Some manufactories are very productive and produce lots of goods, whereas others are more sluggish. Darwin thought the same was true of speciation in nature. Further, he thought that the differences in productivity among different groups of species was consistent through time – the vigorous manufactories of today were also vigorous many years ago.

We used a database of more than twenty five thousand subspecies of birds to test Darwin’s idea. We found, as Darwin predicted, that birds that have lots of subspecies came from larger groups that were also very diverse. This is the first direct test of Darwin’s prediction since he published “The Origin”.

Further, we found that Darwin’s idea helps us to predict which parts of the tree of life are most vulnerable in the current global wave of species extinctions. Specifically, we found that species from groups that are vigorous manufactories of diversity are less likely to be endangered than are species from groups that have produced less diversity. Conservationists may therefore want to prioritize conservation efforts on especially vulnerable parts of the tree of life.