Along the way he will be writing articles, shooting video and tweeting.

Salopek will take some 30 million footsteps during this journey, which he calls "the long walk into our becoming". So there is a lot of potential for blisters.

But he insists he is not doing this as some kind of extreme sport - he will be thinking hard, en route, about human evolution.

The starting point for the trek is Herto Bouri, a site in north-eastern Ethiopia populated by early humans in the Middle Stone Age.

"Paleoanthropologists have found an extremely old Homo sapiens fossil there, which might be as much as 160,000 years old," says Salopek.

This was how we were designed to absorb information, at 5km an hour (3mph)”

"Since the group of people whose footsteps I am following are early homo sapiens, the fit is pretty good."