Anders Ericsson

In particular, a good deal of research has shown that nearly everyone with perfect pitch began musical training at a very young age—generally around three to five years old.

The clear implication is that perfect pitch, far from being a gift bestowed upon only a lucky few, is an ability that pretty much anyone can develop with the right exposure and training. The study has completely rewritten our understanding of perfect pitch

In the millions of years of evolution leading up to modern humans, there were almost certainly no selection pressures favoring people who could identify, say, the precise notes that a bird was singing. Yet here we are today, able to develop perfect pitch with a relatively simple training regimen.