So much higher than what? Than other populations? That depends on the populations being compared. Asia's total population is large, of course, but it's a vast area provided with zones of historically highly productive agriculture.

Or higher than in the past? That goes for nearly all populations, but Asia's share of world population's fallen significantly over the last two centuries, with its average annual growth rate dropping by more than half since 1970.

So some clarification of the question would be helpful.