In what could be referred to as natural selection, it has been discovered that the Bajau people of South-East Asia are born with bigger spleens. This is undoubtedly caused by how they live their life on the ocean and survive by diving for fish and oysters. This lifestyle of continued underwater living caused the Bajau people to develop bigger spleens.
The reason behind this is because bigger spleens allow them to have more oxygen available in their blood for diving. Located very close to the stomach the spleen allows our body to remove old cells from the blood, you could say it is a sort of biological scuba tank for long dives.
The Bajau people are of no fixed country living on the oceans, they number around one million people scattered across the southern Philippines, Indonesia, and Malaysia. For thousands of years, they have lived on houseboats and just traveled from place to place on the waters. Barely ever going onto land, they make sure they get everything they need from the sea.
Their traditional diving consists of spending 60% of their day underwater, from 30-second dives to several minutes they dive down to the depths of 70m. With only a wooden mask or goggles and a weight belt to assist them, this meant the spleen was the natural organ to develop to help their aquatic lifestyle.
When you dive your heart rate slows, your vessels on the extremities contract to preserve the oxygenated blood for vital organs. And then the last thing to contract is your spleen, it is like a reservoir of oxygenated red blood, so when it contracts it gives your body a boost. The Bajau people with their bigger spleens are able to dive longer as their boost is even bigger than normal.