To make a living and feed their families, ancient fishermen, pearl hunters, sponge gatherers, and shipwreck salvagers trained themselves to overcome the all-powerful urge to breathe so they could stay underwater for minutes at a time.
Today you can still find pockets of people who continue to practice the art of unassisted deep-sea diving. For example, the Bajau — sometimes known as the sea gypsies of Malaysia and Indonesia — are renowned natural freedivers. They'll descend to depths of more than 65 feet and stay underwater for up to five minutes, fishing and collecting coins thrown into the water by tourists.
Besides these divers who brave the watery depths in order to make a living, there's a small group of renegade athletes around the world who will freedive to 50x the fathoms of an average swimming pool…for fun.