It’s been said that in times of intense stress or sudden anger, a primitive part of our brain takes control. This irrational aspect of ourselves doesn’t stem from our highly evolved human faculties, but rather from the remnants of our reptilian ancestors that have persisted in our brains despite the process of evolution. Some call it the “lizard brain.”
The lizard brain theory was formulated by neuroscientists in the 1960s, particularly by Paul McLean. As he studied the brains of humans and other animals to explore the origins of negative emotions, he found common behaviors between reptiles and mammals related to survival instincts like establishing routines and defending territory, as well as unique mammalian behaviors.
Through his research and advancements in neuroscience allowing for the comparison of brain structures, MacLean proposed that the human brain evolved from a reptilian brain with ancient lizard characteristics still preserved. He identified three distinct brains within the human brain, which he called the “brain trinity”: the oldest reptilian brain, the paleomammal complex or limbic system, and the new structures that emerged with higher primate evolution.
Despite the popularity of the triune brain theory, recent studies have challenged the notion of the lizard brain. Neuroanatomists have pointed out that the brain is not structured like an onion with successive layers resembling different species’ brains, as the Trinity theory suggests.
For instance, while the amygdala within the limbic system is more developed in primates than in rats, indicating a more complex evolutionary trajectory, the concept of progress in evolution suggests that older animals are more primitive and newer ones more sophisticated. Evolution is not just about adding new features while leaving the old ones unchanged.
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Source: www.sciencefocus.com
