Virtually the entire history of modern humans - from their first appearance some 300,000 years ago to the Industrial Revolution - is attuned to the seasons. Our brains perceive summer as a time of peak fertility and harvest and reward us accordingly with feelings of happiness.
The winter blues and the summer happiness we experience in the Western world are not merely a biological reaction attributable to vitamin D production; rather, they are deeply rooted in our brains.
Studies show that people in colder regions suffer from seasonal mood swings and winter depression significantly more often. The farther one lives from the equator, the more frequently these effects occur. In warmer regions of the world, such as Asia or Africa, there is no such intense surge in feelings of happiness and dopamine release. Instead, many residents of hot regions often even find summer to be a burden. Epidemiological data from tropical climate zones (such as a pioneering study in the Journal of Affective Disorders) support this.
Since our brain still «lives» in the Stone Age, it shapes our subjective and biological reality according to that era. What we consciously think and perceive is irrelevant within the scope of our narrative self. Animal-driven bodily functions dominate humans and therefore define summer as the happiest time of the year. Now leaves are growing on all trees and plants, vegetables are maturing, and, most notably, precious fruits are available to us. It is also a time of abundance for hunting and reproduction. We no longer have to struggle through the freezing cold, shivering and forced to search for animal prey. While hunters and gatherers can primarily only hunt in winter, they can now finally gather again as well.
According to this theory, seasonal mood swings are thus also an expression of an evolutionary mismatch that, in modern times, falsely leads us to believe we still have the resource capacities of the past. Today, we have sufficient food available in both winter and summer, and the care and nourishment of our offspring are also guaranteed - the seasons hardly have any effect on our selective pressures anymore. The feeling of happiness in summer - that is, the subjective perception that summer is more beautiful and makes us happier than winter - is also a remnant of an ancient evaluation mechanism.
In the distant future - perhaps in a few thousand years - our brains will have adapted. We will likely find winter more pleasant then and experience greater feelings of happiness in the snow than under the hot sun. Since we will have sufficient resources essential for survival regardless of the season, evolution will ensure that we no longer perceive summer as particularly significant. In addition, the dopamine axis will shift, as sunlight will then be perceived as an optional but rather harmful influence. Through vitamin D supplementation, exposure to the sun will increasingly be selected as «not essential for survival.» Cold weather will increasingly become the «reward» of the seasons, as it offers the skin and body protection from the sun’s rays, whose UV radiation attacks cells and even genetic material, leading to skin cancer.
With that in mind, perhaps one alternative for modern times would be to find joy in the cold seasons, even if the brain (still) resists it.