Image copyright Melissa Ilardo
Image caption The Bajau subsist by gathering shellfish on the sea floorIn a striking example of natural selection, the Bajau people of South-East Asia have developed bigger spleens for diving, a study shows.
The Bajau are traditionally nomadic and seafaring, and survive by collecting shellfish from the sea floor.
Scientists studying the effect of this lifestyle on their biology found their spleens were larger than those of related people from the region.
The bigger spleen makes more oxygen available in their blood for diving.
The researchers have published their results in the academic journal Cell.
Located close to the stomach, the fist-sized spleen removes old cells from the blood and acts as a biological "scuba tank" during long dives.
The Bajau people live across the southern Philippines, Indonesia and Malaysia and, according to rough estimates, number about one million people.
"For possibly thousands of years, [they] have been living on house ..