One niggling problem on evolution that troubled me for some years is: Why couldn't we - most of the terrestrial vertebrates, I mean - drink seawater ?
On the face of it, the ability is obviously advantageous: the supply of freshwater is very much limited as compared to some sodium chloride solution.
But we could not.
The simple answer is, although there is a surplus of sea water on earth, most of the in-land source, i.e. river and lake, is freshwater. To explore the land, terrestrial animals must be able to drink pure water.
But that's beyond the point ! If animals on land originated from marine ones, they should be able to drink seawater to start with. They may gradually learn how to tolerate lakes and rivers when the species explore the land, but what we are seeing is their selective loss of an ability that they used to have - and a very valuable one in terms of competition.
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2 comments:
But is it possible for one organism to tolerate both seawater and fresh-water at the same time? If not and you have to choose one, I think drinking fresh-water was probably more competitive for primitive inland organisms (you know, they didn't get pumps, drain-pipes, tanks etc). Only the perimeter of land is approachable to sea water, but fresh water is available inland whenever there are river, lakes, raining etc.
That's also why properties with seaview are so much more expensive, proofing that proximity to seashore is actually a very scare resource.
My humble view is that life will be miserable if you cannot taste sweet. Freshwater vertebrates are more happy than their salty counterparts so they reproduced more and eventually outnumbered the latter.
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