Did you know:
Your hypothalamus (think big brain control center) tells your body what temperature to maintain. If you’re sick, your immune system will release chemicals that cause your hypothalamus to increase your thermostat. A fever. You’ve probably had one. Your blood vessels constrict. You shiver to increase muscle heat. Your muscle is broken down to make heat.
But if your hypothalamus can induce behavioral changes to make you warmer: put on more clothes, get in certain body positions. And if you introduce the equivalent chemicals into fish, they swim toward warmer water to warm themselves. And with lizards, they’ll seek sunlight.