The brain size of a human is about 2.4 percent of our corrected body mass, meaning compared to the body mass of a ‘normal’ weight and size human body. And yes, generally speaking men’s brains are slightly larger that women’s brains and the sexual drive component of a man’s brain is three times the size of that component in a women’s brain (which explains a lot).
Just recently I have come across a number of articles about the brains in other animals and I was sort of surprised to find out that many other animals have much larger brains in relative terms.
Some birds, for example the common old crow, has a brain mass of 6 percent thereby giving crows a brain that is 2.5 times larger than a human brain in relative terms.
Ants have brains that are 15 percent of their body mass which gives them a brain that is, in relative terms, over six times bigger than a human brain.
Then today I came across this article on the Smithsonian site that says that some spiders have a brain mass that is 25 percent of their body mass. This gives these spiders a brain that is 10 times the relative size of a human brain.
Who would have thought spiders were so damn smart?
But hang on. Spiders have tiny little heads. No way you can get a brain mass comprising 25 percent of their body into that. Just can’t happen. I mean, look at red back spiders for example. Their head is almost too small to see.
Well it seems spiders don’t keep all their brains in their head. Their brains are distributed across other parts of their body. How frigging cool is that? If you shot a spider in the head (if you had a small enough gun and really good aim) you wouldn’t shut down its brain. In fact you would only get about 20 percent of the brain. To me this seems like a much better plan than with us; having such a vital organ all massed together and then stuck up there on top making it a mighty fine target for anyone with a club or a gun.
Yep. A spider’s brain and central nervous system control centre is distributed around the body including the legs—which contain about 25 percent of the brain. So if you break off one of a spider’s legs you are are also destroying about three percent of their brain function.