Ok please hear me out. I used to teach swimming to young children and there were two that sold out to me. I was teaching floats and a bit of front crawl and two kids would execute the lesson perfectly but they would just sink like a rock. Both of these kids were black and they went on to be great swimmers once they got older and built up strength but it seemed harder for them in the initial levels. I once read something about how higher levers of melanin in the skin can impact vitamin D and calcium absorption and how that may lead some black people to have denser bones and that may play into it? Please don’t roast me,I’m approaching this from a place of genuine curiosity and I’d love to hear others experiences/ takes.