Over hundreds if not thousands of years, however, a group of Southeast Asian “sea nomads” known for their deep-diving prowess has evolved larger spleens. The spleen holds oxygenated red blood cells, so presumably an enlarged spleen – those of the sea nomads, or Bajau people, are about 50 percent larger than the spleens of unrelated, non-diving neighboring groups – injects more blood cells into the circulation and makes more oxygen available for basic body functions during prolonged dives.