According to Nature, about 37,000 PhDs are awarded annually.
If there were that many degree recipients during the last 100 years (and there weren’t), and if all of them are still alive (they aren’t), then there’d be 3.7 million people with a PhD.
As an upper bound, that’s a quite small number. Or, inversely, we constitute less than about 0.05% of the world population.
