The final episode shows how the megafauna become extinct, and about how modern animals living on the continent have adapted to the increasing human population and development in North America. The meeting between human and megafauna in North America was a deadly one - most of the large land animals, including all the mammoths and mastodons, horses, camels, giant ground sloths, short-faced bear, and all the big cats (except the cougar) disappeared and the landscape changed dramatically. But some animals learned to flourish in human's environment. Today chimney swifts roost in the towering smokestacks of Portland, kit foxes den in Los Angeles suburbs, moose trample the gardens of Anchorage and red tailed hawks nest in Manhattan.

• Jack Fortune