Beyond Our Lizard Brain

Lizards and humans share similar brain parts, which they inherited from fish. These parts handle basic body functions like breathing, balance, and coordination, and simple survival urges like feeding, mating, and defense. Together, these parts--the brain stem, cerebellum, and basal ganglia--are casually referred to as your "lizard brain." So how are mammals different from lizards?

How it Works

One big difference between mammals and lizards is that mammals have more complex emotions. Our emotions are processed in several regions that together are loosely called the "limbic system." They form a ring around our "lizard brain" regions, which evolved earlier. Mammal brains also have an outer layer called a cortex, which helps us control our emotions and make complex decisions.

Mammals tend to have strong emotional bonds between family members, and they generally care for their young after birth. Instead of responding just by reflex and instinct--as a lizard does when it snaps at you if you get too close--they are guided by their emotions, making their behavior more flexible. Mammals tend to have good memories, especially for events that created strong emotions.

Primates--the group of mammals that includes monkeys, apes, and humans--can recognize facial expressions, communicate, maintain social relationships, and sometimes even lie, thanks to the front of their cortex, or outer layer of the brain. A monkey's cortex is more than twice the size of a comparable mammal's, and in humans, it is bigger still. All mammals have some version of basic emotions like fear and anger, since our limbic systems are very similar. But humans are also especially sensitive to social emotions like shame, guilt and pride, which require understanding what other people think and feel about us--a specialty of our advanced prefrontal cortex.

The human brain includes many regions that evolved long ago. Our older "lizard brain" parts keep our bodies working and provide basic survival motivations, while our newer "mammal brain" regions improve our emotions and memory. Our "primate brain," with its large, wrinkly cortex, helps us plan, predict, and use language. All these regions work together. So while ancient urges still drive our behavior, we constantly think up new strategies for achieving these goals.