Horses almost went extinct

Imagine human development without horses.

Modern members of the Equidae family, including horses, all originate from North America (which was isolated from the other continents at that time, at around 18 million years ago).

Towards the end of the time period that the Equidae family was already declining (starting roughly 6 million years ago), the Bering land bridge reopened. Mind you, this was after 18 million years of history, just to give you a scope of the timelines we're working with.

This seemed to allow the remnants of the Equidae to graze in greener pastures in the old world. Unfortunately for those left in the Americas, the combination of an ice age and the influx of humans flowing the other way across the land bridge led to their extinction^[1].

After proliferating throughout the Old World, it seems that humans around the steppes north of the Black Sea (modern day Ukraine and Kazakhstan) domesticated them around 6,000 BCE.

Curiously, the history of horses goes full circle, making their way back to the Americas via Christopher Columbus on his second voyage to the Americas.