On the face of it

What is remarkable about the way we appear is that each individual face has a recognisable, near-unique pattern. Of course, there are exceptions. Identical twins can have near-identical faces. That, along with the fact that people can look a lot like their close relatives, gives us a hint that the process that shapes our faces must have a strong inherited component. To us, at least, other animals do not appear to have readily distinguishable facial features among individuals. Those who pay attention can tell one rhesus macaque from another by looking at their faces, but to most of us, one monkey looks the same as another. Yet whether it is a monkey, a donkey, a cat, a bird or a human, the toolkit and the machinery used to shape the face are very similar. What this mechanism is, and why there is so much individual variation in some species, such as humans, and much less so in others, have been studied for long, and many aspects understood.