Why is the brain stem sometimes refered to the reptilian brain?

The brain stem is sometimes referred to as the "reptilian brain" because it is responsible for basic survival functions such as breathing, heart rate, and reflexes, which are essential for immediate survival. This terminology stems from the evolutionary perspective that these functions are similar to those of reptiles, which possess a simpler nervous system focused on survival and instinctual behaviors. The concept highlights the brain stem's role in regulating fundamental life processes, contrasting with more complex cognitive functions associated with the neocortex.