The Bajau people of Southeast Asia have been living at sea for the past thousand years, perfecting the art of free-diving better than anyone on earth. They are submerged for about five hours every day as they gather food in depths of more than 70 metres. As a result, the Bajau are the only humans that have genetically evolved to store more haemoglobin-rich blood for longer breathes, they are able to resist low oxygenated conditions and their evolutioned gens also govern that more blood is sent to vital organs instead of to limbs. They don't have gills yet, but that's a matter of time.