Ever wondered why every animal doesn't evolve a complex, flexible, problem solving brain like humans? Brains are expensive.

The brain, unlike any other organ, runs only on sugar. Thinking hard requires more glucose than relaxing & zoning out. When you are asked to do a thinking task & say "I'm too tired" -it's is real!

~20% of calories go to the brain. If a rabbit wanted to expand its gray matter it would need more food-- being a little smarter doesn't always translate into better survival.