Why did human development proceed at such different rates on different continents for the last 13,000 years?

The broadest pattern of history - namely, the differences between human societies on different continents - seems to me to be attributable to differences among continental environments, and not to biological differences among peoples themselves.

Guns, Germs, and Steel: The Fates of Human Societies.

Human societies vary in lots of independent factors affecting their openness to innovation.

Introspection and preserved writings give us far more insight into the ways of past humans than we have into the ways of past dinosaurs. For that reason, I'm optimistic that we can eventually arrive at convincing explanations for these broadest patterns of human history.

All human societies go through fads in which they temporarily either adopt practices of little use or else abandon practices of considerable use.