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>The thing is that we need a fairly careful balance between salt and fluid in our bodies True, but we ingest all sorts of substances in amounts that we don't n
by fauigerzigerk 9y ago
>The thing is that we need a fairly careful balance between salt and fluid in our bodies
True, but we ingest all sorts of substances in amounts that we don't need. The rest is usually excreted unless having a store of it is useful (like with fat).
- jacquesm 9y agoWe excrete a lot of salt already, kidneys do hard work. Ingesting salt water would quickly overwhelm their capability to shed the salt. Incidentally, this kind of over-concentration+some kernel to start crystallization around can cause kidneystones.
- fauigerzigerk 9y agoThat's all true, but you're merely describing the status quo. I'm asking why our kidneys (and those of most other mammals) have not evolved to process sea water. Apparently there was not enough evolutionary pressure and that is what I find very surprising.
- jacquesm 9y agoThe subjects to study would be Cetacea, there should be at least a partial answer there: https://en.wikipedia.org/wiki/Cetacea https://en.wikipedia.org/wiki/Cetacea There is this bit: "The kidneys are long and flattened. The salt concentration in cetacean blood is lower than that in seawater, requiring kidneys to excrete salt. This allows the animals to drink seawater." So for those animals that returned to the sea from the land that pressure was there and they seem to have adapted in that sense. Humans - and most other mammals - being land dwellers we always had access to rivers and rainfall both of which are fresh.