This paper is a nothing burger. Diamond’s analysis was not single factor. But if we stick with geography, how many isthmuses create bottlenecks for migration

This paper is a nothing burger. Diamond’s analysis was not single factor. But if we stick with geography, how many isthmuses create bottlenecks for migration annd exchange across Eurasia? Look at the Middle East, which touches the Nile, the Mediterranean, the Black, Caspian and Red Seas, and the Tigris and Euphrates. How much of it is within 100 miles of temperate and navigable water?Now look at North America. It was easier to convert energy to motion over long distances in a denser network of trade at the nexus of Eurasia.