How evolutionary developmental psychology can explain mental disorders

Why are mental disorders like depression so common? Psychologists Maren Hoogland and Anemi Ploeger analyzed the three main theories of evolutionary developmental psychology to find the best explanation for mental disorders. All three of these theories link mental problems to a mismatch in our development. The researchers believe that combining the three theories will help us understand mental disorders and improve treatment. Their findings are now published in a journal Perspectives of psychological science.

Hoogland and Ploeger specialize in the evolutionary causes of mental health problems: what role do humans play childhood experience, how important is their genetic makeup, and what is the impact of adaptations from our evolutionary past? In their new study, they combined three major theories of evolutionary developmental psychology to find a common explanation mental disorders.

Evolutionary inconsistencies

“The first theory involves the concept of evolutionary mismatch,” Hoogland and Ploeger explain. “Evolutionary mismatch means that the difference between our current environment and the one in which we evolved is so great that our bodies and minds can no longer keep up with all the innovations.”

They cite modern sedentary lifestyles, the processed foods we eat, and the ever-present smartphone as examples. “These are circumstances that humans are ill-adapted to, and that’s why we call them evolutionary mismatches. They can lead not only to diseases like diabetes and Cardiovascular diseasebut also to mental disorders such as depression.’

Individual developmental discrepancies

The second theory deals with developmental inconsistency. “To what extent does your current environment resemble the one you grew up in? If these worlds are too far apart, your adult mind is overloaded with so many new experiences that you are barely able to adapt to the current environment,” the researchers explain.

“Let’s say, for example, that you grew up in a very peaceful environment and now live in a noisy city, or that you are poorly educated and about to go to university. Such individual developmental inconsistencies can also lead to illness and mental health problems.”

Individual differences

The third and final theory about individual differences. “Some people remain stable despite stressful events or unhealthy eating habits, while others may develop disease under the same circumstances or as a result of a minor setback. How can such significant individual differences be explained?”

The theory of differential susceptibility states that some people are more sensitive to environmental conditions than others for genetic reasons. This may be due to how they were raised, as well as lifestyle factors such as diet and exercise.

However, earlier studies based on this theories shows that people from unhealthy lifestyle who develop illness in response to negative experiences actually thrive in a more positive environment.

“This means that the same genes are associated with both extremely high coping ability (in a positive environment) and low coping ability (in a negative environment).” In other words, these genes determine a person’s sensitivity to the environment. “In contrast, people with a different genetic makeup can remain perfectly stable no matter what life throws at them.”

All three theories are necessary to provide an explanation

According to Hoogland and Ploger, you need to combine elements of all three theories to find a satisfactory explanation of what causes mental disorders like depression. “Many therapists know that traumatic experiences in childhood can contribute to the development of mental health problems, but not that the vast differences between a person’s childhood environment and the environment in which he lives as an adult also contribute to it.”

Hoogland and Ploeger also believe that therapists are often unaware of evolutionary mismatches and the extent to which they can cause disorders. “Finally, they often do not know that people who are relatively susceptible to mental health problems can actually thrive in the positive environment.” Hoogland en Ploeger conclude that these ideas may lead to better treatments.