According to David Linden a professor of neuroscience at Johns Hopkins University, the human brain relies heavily on structures found in lower animals. These functions play key roles in our everyday life.

A lizard brain is about survival — it controls heart rate and breathing, and processes information from the eyes and ears and mouth.

When mammals like mice came along, the lizard brain didn’t go away. The evolution slapped more brain on top of the lizard brain which then became the brain stem. These new parts gave mammals more memory and a wider range of emotions. It also allows them to do things a lizard can’t, like using experiences to anticipate danger instead of just responding to it.

And then the evolution added another layer to the brain that allows for example apes to reason and live much more complicated lives than mice.

In these brains you can find all of the very same parts that you would see in a human brain; except that the brain of an adult human is about three times the size of a gorilla brain. Much of the size difference appears after birth. The human brain continues to grow rapidly for the first five years after birth. It takes 20 years before all the circuits are laid out and connected up, Linden says.

As a result of having a bif size brain, there are enough neurons in our cortical circuit, massively interconnected, that the amazing human traits emerges from, such as: the ability to know what others are thinking based on social cues that people give them, other forms of observational learning and high-level cognition.

…and the highest payoff of our massive brain is the feeling of love and compassion.

Source: N.P.R; Jon Hamilton, August 9, 2010