Our brains are made out of the same stuff as any other animal's brain-- our brains are just a lot bigger! Brains are made out of neurons: long cells that communicate with each other through electrical and chemical signals. Human brains are made out of billions neurons, and each neuron has channels to communicate with thousands of other neurons-- so it's not just the size of out brains that makes us smart, it's how our neurons are connected.

No matter how big a brain is, however, its neurons still work in the same way. This is why neuroscientists can do studies on mice and other animals and still learn something about how the human brain works! In fact, one of the most important discoveries in neuroscience was made by Eric Kandel when he was studying sea slugs. Sea slugs only have about 20,000 neurons in their whole body, so they're a lot easier to study than humans who have about 100,000,000,000 in their brain alone. Dr. Kandel noticed that when sea slugs are in danger they react by protecting their gill, the organ they use to breathe. If you keep bothering a sea slug but don't actually hurt it, they'll eventually stop protecting their gill because they learn that you're not a threat. This is called habituation. Sea slugs also exhibit sensitization when they are actually harmed, and afterward they react even more strongly to protect their gills. Habituation and sensitization are types of learning. Since sea slug neurons and human neurons work in about the same way, studying how sea slug neurons learn and make connections can teach us something about human neurons. Dr. Kandel had this insight in the late 1970's, and in 2000 he won a Nobel Prize for his important research.

There are many functions of the brain that have remained much the same in animals, despite other evolutionary changes. Learning and memory, as Dr. Kandel described in sea slugs, is just one of those functions. Other mechanisms seem to work in similar ways across species, including eating, drinking, breathing, sleeping, reward, and even love!

Brains all work pretty much the same way.If you study animals with backbones (vertebrates), you find that the cells look the same and the chemistry is the same whether were talking about fish, frogs, or humans. The shapes of our brains are a bit different, and some of the parts of the brain are bigger or smaller. For example, a dog uses a lot more of its brain to process smells than we do.

It would seem like a small brain would mean an animal wasnt very smart, but what really makes a difference is the proportional size of a brain. This just means that you need to look at brain size as a fraction of body size to get a better understanding of intelligence. A bigger animal has bigger muscles to control and more information coming in from sensors in their skin, so it takes more brain to process the information. Theres a nice graph of body size and brain size here:

You can see that humans are above the line, meaning that our brains are bigger than you would expect given our body size. This extra amount of brain is mostly in the area that does complicated things like planning for the future. Hippos are below the line, meaning that their brains are smaller than you would expect. They may not have as much intelligence as a horse, which is smaller, but has the same size brain. Animals dont tend to have larger brains than they need because brains burn a lot of calories, and food is often a limited resource. What kinds of things might an animal have to do that would call for a larger brain? Theres more to the story than brain size, or even proportional size. Geniuses dont tend to have larger brains. We are still learning about the brain, and there is a lot we dont know yet. If you want to discover some of these secrets, you may be interested in a career in neurobiology.