Because we see the brain through the lens of evolutionary theory, it is important to consider how the human brain has changed across evolution. We make inferences about how our brain has evolved based on comparisons between human and animal brains. For one, our brain has become much larger relative to our body size. Evolutionarily older and more primitive animals have much smaller brains relative to their body size. Think of the dinosaurs with their tiny brains and huge bodies. In fact, our brains are about three times the size of the brains of our closest relative, the chimpanzee, although our bodies are not much bigger than theirs. Secondly, the brain has become much more complex. It is less the size of an animal’s brain that determines its intelligence than the complexity of its neuronal networks. Billions of neurons create trillions of connections. Brain size and brain complexity, however, do tend to go together.