The shape of the animal kingdom, as we see it today, has been sculpted both by origins and by extinctions. Having examined extinctions, we now return to the more positive side of the evolutionary process: origins. But what, in an evolutionary context, is an origin? Every species of animal that has ever lived began by evolutionary modification of its parent species. And all animal groups (or clades, as we now think of them) have their origins within other clades – such as the birds within the dinosaur clade, as we noted in the previous chapter. There is no such thing as the magical de novo origin of any new animal species, or any new animal group, devoid of a history of ancestors.

Having said that, some origins are inherently more interesting than others, and for at least two reasons. At the level of the individual animal species, there is more interest in the origin of Homo sapiens than of any other species for the obvious reason that we are particularly fascinated by our own roots. And this kind of self-interest can extend from individual species to higher-level groups – for example, going back through time, to the origin of the primates, the mammals and the vertebrates.