I know that the heart is made of cardiac muscle, why supposedly never fatigues or weakens. So why can’t our skeletal muscles also be made of cardiac muscle? It would give us a ton of endurance in life or death situations and make us even better runners to escape from predators.
In: Biology
Everything is a trade off. Cardiac muscle is hard to fatigue, but requires a ton of energy to maintain. Our bodies don’t like to waste energy hard to maintain things – energy was scarce, so conservation and efficiency were essential to survival.
Skeletal muscle gave us the right balance of enough strength and endurance to get the job done without the higher energy demands.
Also, because our brains evolved over other mammals homo sapiens started to dominate other ‘primates’ with the bodies they had.
It uses a TON more energy. You’d need to eat like 10,000 calories a day to not starve to death. It’s just not worth it for the boost during rare life or death situations, because now *every day* becomes a life or death situation needing to find and eat food the whole day so you don’t die.
Also remember that food becoming plentiful happened very very recently in evolution terms. Food was scarce and *unpredictable* for a million years before that. Something that helps you in some situations but ups your food requirements by like 5x *every day* is overall not an advantage in a world with food scarcity. So only our mission-critical heart muscle proved to be worth upgrading.
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