The Bajau people of Indonesia are known as “Sea Nomads,” because we’ve known that for thousands of years they live in houseboats, sustaining their diets after spending hours each day hunting fish or other sea creatures underwater. Bajau divers can spend up to 13 minutes free diving to 70 m depths underwater all with only weights and traditional wooden goggles. This ability is requires unique adaptations.
Melissa Ann Ilardo studied this group and their adaptations. Last Thursday she published her findings in the journal Cell. Ultrasounds of their spleens show that they are about 50% larger than other nearby populations, similar to seals, which functions in oxygen delivery and hemoglobin concentrations. During the diving response, the spleen contracts, which injects oxygenated blood cells into the circulatory system, acting as the fuel partly responsible for allowing us to hold our breaths.
Curiously, this hypersplenism in the Balau people occurred whether they were regular divers or not. Further analysis of their DNA revealed why. After sequencing the genomes of a few dozen Bajau and Saluans, the researchers found that the Bajau had much higher frequency of a variant of specific gene, called the PDE10A, associated with spleen size. This genetic variant existed before the Bajau, because the Saluan have it, too. But once they diverged it became advantageous for Bajau individuals to have this after the Bajau adapted to this particular lifestyle.