Final answer:
Humans and cats have evolved to live in a state of homeostasis, but can switch to a fight-or-flight response when faced with stress. This response is associated with the autonomic nervous system and although vital for ancestral survival, it can have negative health impacts in today's psychological stress scenarios.
Step-by-step explanation:
Cats, and probably humans, too, were evolved to spend most of their time in a mode of homeostasis, with the capacity to confront a stress-inducing threat when we experience the reflex known as the fight-or-flight response. This response set of reactions is induced by sympathetic activity that leads to either fleeing a threat or standing up to it. In the modern world, the stimuli that trigger this response are often psychological rather than physical, such as giving a presentation or taking a big test. While this response was necessary for survival in the face of predators and dangers in the ancestral environment, constant exposure to psychological threats can lead to negative health consequences today, such as an increase in susceptibility to heart disease and impaired function of the immune system due to stress reactivity.
The autonomic nervous system is responsible for these reactions, and such adaptations probably predate the human species. It is suggested that this system and the fight-or-flight response it generates are common to all mammals and may be shared by many animals. Understanding that our stress response system was shaped by prehistoric conditions can help us recognize how it might not always be adaptive in today's modern environment. Our ability to adapt to such stressful situations is partially homeostatic, aiming to bring the body back to an optimal state of equilibrium, and partially allostatic, preparing for and anticipating future situations.