Why can I float in water without doing anything?

I'm pretty sure everyone can float in water despite their size, if they relax, it's all because you will weigh less than the water you are displacing, water is suprisngly heavy, 1m^3 of water weighs a tonne. But also I guess if you have a slightly larger surface area then you will find floating on top of the water slightly easier, but the other people you mentioned would be able to do it if they tried hard enough.