Brain Rules: 12 Principles for Surviving and Thriving at Work, Home, and School

Throughout Brain Rules, Medina explores how evolution has shaped the human brain to be a remarkable processor capable of growth, memory, and symbolic reasoning. He suggests that the reason human brains are so unique is that they evolved this way; they found an advantage through complex processing capabilities. For each brain rule, Medina attempts to understand the evolutionary advantage. He recognizes that sleep—while leaving humans in a vulnerable state—helps to encode and process information that ensures later survival. He reveals how the cognitive preference for sight sensation is reflective of a need to survive in the wild, where humans took in billions of visual data points. In some cases, Medina is not able to determine the evolutionary value of the rule; for example, he cannot directly pinpoint the impact music has on cognitive function and emotion. However, the connection is undeniable, and the evolution of the brain is a story of intention.

Contemporary culture often functions in a way that conflicts with the evolutionary workings of the brain. Cultural norms often do not capitalize on the way brains are designed to function. One example of this is multitasking. Medina suggests that the brain is not wired for multitasking. In fact, it is most capable when it devotes attention to singular concepts and tasks. Yet, modern culture emphasizes the importance of multitasking and rewards multitasking behaviors. Many people listen to music or talk on the phone while driving, despite significant evidence that they can only do one of those things with their complete attention. Another example is movement. Humans were designed for movement. Medina suggests that human ancestors walked approximately 12 miles a day. Walking was a necessity. It led humans to food and safer campsites. Humans who sat still for long periods of time were vulnerable to attack by predators. Yet, in our current society, incoming emails from powerful figures cause stress while we sit for long periods at computers. Those powerful figures would find increased productivity if they encouraged workers to take breaks and walk.

While evolution has brought many benefits to the human brain, it has also complicated things. For example, Medina explains that the invention of civilization has decreased humans’ overall physical activity. This contributes to cognitive decline and illnesses such as stroke. The same system that contributed to the advancement and success of the human species also provided its Achilles heel. The brain has also developed a finely tuned system for coping with stress, but this system does not always adapt well to modern stressors. Medina explains that humans are not hardwired for long-term stress; their bodies have adapted to deal with short bursts of intense stress—such as an attack from a predator or a change in the weather. Prolonged and intense stress is a modern invention, and it can have a deteriorating effect on memory and cognitive performance and produce a host of physiological ailments.

The evolution of the brain does not live only in history. Medina reveals how brains shift and grow based upon experience and learning. The final chapter looks at infants and children and shows how the same strategies used for learning in these stages translate to adult learning. Humans are hardwired to be explorers and to acquire knowledge. Doing so gives them an evolutionary advantage. While the same learning has conjured myriad problems in contemporary society and contributed to devastating climate change, this learning also provides a foundation for the extreme adaptability and cognitive power of the species.