Thanks, I was just wishing that this article would have gone into that. Presumably whales and other marine mammals can drink ocean water -- how else would that

Thanks, I was just wishing that this article would have gone into that. Presumably whales and other marine mammals can drink ocean water -- how else would that work? -- so it's not an inevitable design constraint that our internal salinity is less than that of the ocean. Presumably our ancestors evolved to drink low-salinity water (and eat separate sources of salts, and automatically mix the correct salts into the water in the correct proportions, and maintain those proportions at all costs -- lots of overhead!) because fresh water is what's plentiful in our habitat. In other words, it's because lakes, rivers, and springs yield fresh water that we've evolved all these mechanisms for tolerating fresh water. Another nice poetic question is: why are we made of so much water? The answer is that life evolved in the ocean. We're built out of crucial parts that were developed in the ocean and that can't operate outside of a saltwater environment. So life colonized the land by evolving a way to carry its own ocean with it. ;) I'm a giant EVA unit for ocean-dwelling cells!