Another way that the human brain has changed across evolution is the growth of the cortex. The neocortex, the six-layer tissue that forms the outer layer of the human brain, is found only in mammals. Primitive cortices are evident in smaller mammals, such as hares, opossums, and armadillos, and more developed cortices are evident in higher-order mammals, such as elephants, dogs, and dolphins. In humans, the cortex wraps around the entire brain. The cortex allows for much more sophisticated processing of sensory information (e.g. sight, sound, touch). It also allows for more varied and flexible behavioral responses to internal and external stimulation.