A human with the metabolism of a hummingbird would need to eat about 80,000 calories a day to survive. Why? Because staying warm by making your own heat takes up a lot of energy.

Given that earth’s largest animals have to spend most of their day eating to keep their heat engines running, why aren’t humans cold-blooded… like crocodiles? Here is what science offers as an answer, so far.

View the original video here.

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