Pearl divers adapt their bodies to the ocean by learning to hold their breath for extended periods and developing exceptional underwater vision. Crucial to extended underwater breath control is slowing the pulse and metabolism down to make more effective use of oxygen. The elevated pressure underwater also serves to compress the spleen, so that the blood is richer in hemoglobin and therefore oxygen.
These adaptations are especially pronounced among isolated coastal populations where children learn to free-dive from a young age. Such populations cultivate these skills for various reasons, including sponge collecting and fishing or harvesting seafood, as well as diving for pearls.
The Bajau of Malaysia and Indonesia, for instance, live in homes surrounded by water, often far from any landmass. As a result of spending extended periods in the ocean from a young age, their eye muscles have adapted to pick up more light by constricting and changing the shape of their lenses.
The Bajau have also got significantly lower levels of body fat than the average human. As well making better use of oxygen, this physique allows them to traverse the ocean floor with little buoyancy.
These adaptations are not entirely without cost, however. Among the Bajau, hearing problems are prevalent due to pressure-damage to their eardrums.