The Human Advantage: A New Understanding of How Our Brain Became Remarkable

"This is a really intriguing book by a scientist who’s a neurologist. She didn’t start off being interested in longevity or aging at all. What she was really interested in was trying to understand why humans are cleverer than elephants. Elephants’ brains are three times bigger than ours, so why aren’t they three times as smart? What we have is a particularly big brain for our body size. If you took another animal that’s of comparable size, like a small zebra, it has a brain that’s a fifth the size of ours. So we’re really an outlier. The way that people have always approached this before is by measuring the volume of different parts of the brain. What Herculano-Houzel does in this book is invent a way to actually count the number of brain cells in certain areas. You might think an elephant with a brain three times as big would have three times the number of brain cells, but it turns out that’s not true. She figured out that by basically turning the brain into soup—so you can’t do this on anything that’s alive—you can count the number of nuclei. What she discovered is that in the cortex, the thinking part of the brain, humans have three times as many neurons or brain cells as elephants do, which is remarkable. For a long time, people have thought that brain size relative to body size also affects longevity. So one of the reasons that people are long-lived for a mammal of their size is because they have a bigger brain. I’ve always thought that’s speciesism or pride. What she found out is that if she plotted how long animals live against the number of cells in their brain, humans fell right on the line, rather than being this big outlier that they were previously. The other interesting thing that she discovered is that domesticated dogs have an incredibly large number of cells in the thinking part of their brain, the cortex. A dog has more cells, for instance, than a grizzly bear, which has a brain three times bigger. The fascinating thing is the way that she came up with this technique and applied it to dozens and dozens and dozens of species and then explained the world. She thinks it’s also important in explaining development, how long it takes you to reach puberty. The more cells you have in the thinking part of your brain, the longer it will take you to reach puberty. So I just found her whole story of how she discovered this, and how she up-ended a lot of what people thought about what was going on in our brains by simply being able to count the cells, intriguing. I don’t think there are implications in terms of changing longevity. The implication is only in explaining why we’re so exceptionally long-lived, because we are the longest-lived terrestrial mammal. Actually, traditional societies and, say, hunter-gatherer societies were just a smidgen longer-lived than elephants. Elephants are pretty close. Bigger animals should live longer, and that’s probably one of the most robust patterns in nature. A horse is going to live longer than a mouse. A pattern emerges in hundreds and hundreds of species’ longevity that we really didn’t appreciate before. So I thought it was fascinating from that perspective, the way she develops this idea behind longevity, that our brain really dictates everything that goes on internally and externally."