DURHAM, N.C. — Mothers now have scientific evidence to back up their status as some of the toughest people on the planet.

A recent study out of Duke University shows how pregnancy is one of the most grueling things a human being can do.

"Out there on the very far end of human endurance, the longest-lasting human event you can do with the highest energy expenditure is pregnancy," said Duke University evolutionary anthropology professor Herman Pontzer, who co-authored the study.

Pontzer studied some of the longest races in the world including the Tour de France and the 2015 Race Across the USA which was a 3,000-mile run across the country. 

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