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The elements any particular animal needs are relatively predictable. They are predictable based on the past: what an animal’s ancestors needed is likely to be what that animal also needs. Taste preference, therefore, can be hardwired. Consider sodium (Na). The bodies of terrestrial vertebrates, including those of mammals, tend to have a concentration of sodium nearly fifty times that of the primary producers on land, plants.

This is, in part, because vertebrates evolved in the sea and so evolved cells dependent upon the ingredients that were common in the sea, including sodium. To remedy the difference between their needs for sodium and that available in plants, herbivores can eat fifty times more plant material than they otherwise need (and eliminate the excess). Or they can seek out other sources of sodium. The salt taste receptor rewards animals for doing the latter, seeking out salt in order to satisfy their great need.

What does "otherwise" in the passage above refer to?

a) "If there is no necessity to remedy the difference between their needs for sodium and that available in plants", would be right?

Or

b) "If they did not evolve in the sea"?

Are there any better alternatives?

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  • the "unreal, hypothetical" scenario referenced by otherwise here would be if vertebrates hadn't evolved in the sea and thus would not have evolved cells that were dependent upon the ingredients that were common in the sea. If that were the case, they wouldn't need 50 times more salt than is present in their primary plant-based food sources. But animals did evolve in the sea, so they do need to do something to overcome that imbalance. And finding a salt lick would probably be a lot easier than eating 50 times as much grass as they do already! :) Commented Dec 8, 2021 at 13:56

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"Otherwise" in this context means "for other things". So, "eat fifty times more plant material than they otherwise need" means "eat fifty times more plant material than they would need for other nutritional requirements".

A similar example:

"I help with repairs when I am not otherwise occupied" -- when I'm not busy doing something else

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