Michael_Booth posted...
Okay, a question:
How long is "very recently"?
Because the The Bajau people, often referred to as Sea Nomads, have lived an entirely marine-dependent existence, traveling the Southeast Asian seas on houseboats for over 1,000 years.
Also, the Bajau have genetic differences leading to diving-related phenotypes, specifically an enlarged spleen caused by a mutation on the PDE10A gene.
So a very small group that has specifically divergent evolutionary traits giving them an upper hand at swimming?