The complicated question of how many of us there are

Remember the population explosion? Back in the 1960s, when overpopulation was considered such an imminent threat that President Richard Nixon spoke of the need to address it, the world’s population was moving past 3.5 billion. Today it’s more than 7.5 billion.

Without question, this increase in our numbers has contributed to a host of problems, from resource depletion to frictions over immigration. But the way we think and talk about overpopulation is vastly different than it was when there were half as many of us to worry about it.