eli5: Why can some animals survive without food & water for significantly longer than humans?
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Bigger brain requires more sustenance is one of the reasons, also the fact humans bodys havent evolved for the sake of survival in a really long time, devolved some might even say
Different (and slower) metabolism.
We (humans and most other mammals) need constant intake of calories because we keep our own internal temperature (Homeostasis), we’re warm blooded. We’re quite literally burning calories (combining carbohydrates, or sugar, with oxygen) to generate energy and heat. This means we can very quickly run out of fuel and starve. Some mammals can hibernate, which is sort of controlled hypothermia, where all their processes slow down and their internal temperature drops. But their bodies are specially accustomed to that. You would need to do some serious work to allow a human (or most other mammals) to hibernate. Amd they could still die.
Most other animals are cold-blooded. They do not need to use energy to generate heat, they live according to the heat from their environment. This means that their energy requirement is minimal, so as long as they sit still and digest, they can have only one meal every once in a while.
Metabolism differences. Spiders for instance have a metabolism speed 50% less than any other creature their size. They also have a low effort lifestyle with minimal movement compared to busy humans, so they don’t burn nearly as much energy, and so don’t need to replace it often. The same applies to water, which they get from their food and do not drink as we humans do. They are so sedentary and their metabolism so slow, that some can go two years without food.
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