Most people are familiar with the idea that the seasons influence our mood. Many feel more energetic in the spring, enjoy the long days in the summer, and find winter to be a quieter or more contemplative time. What is less well known, however, is that our moral beliefs may also change over the course of the year. A large-scale study by the University of British Columbia (UBC), published in the Proceedings of the National Academy of Sciences (PNAS), provides evidence that people place greater emphasis on certain moral values in the spring and fall than in the summer or winter. The findings open up exciting perspectives on the question of how closely our decisions are linked to biological rhythms.

Moral Values Are Not as Immutable as Long Believed

In psychology, moral values are considered the central foundation of our social coexistence. They influence how we judge right and wrong, whom we trust, which political decisions we support, and how we respond to societal challenges. It was long assumed that these values remain largely stable in adulthood. The new study challenges this assumption, at least in part.

The researchers analyzed the responses of more than 230,000 participants from the United States who had completed the so-called Moral Foundations Questionnaire over a period of ten years. Supplementary data sets from Canada and Australia showed comparable seasonal patterns. This allowed the scientists to rule out the possibility that this was merely a coincidence or a regionally limited phenomenon.

Which Moral Values Were Examined?

The study is based on the theory of Moral Foundations, which posits that moral thinking is grounded in several universal value dimensions. Particular focus was placed on the so-called binding moral values. These include loyalty to one’s own group, respect for authority, and purity in the sense of social or cultural norms. These values promote cohesion within a community and are often associated with more conservative political attitudes.

In contrast are the more individually oriented values of care and fairness. They emphasize compassion, the protection of others, and the equal treatment of all people, and are more frequently associated with liberal values.

The analysis revealed a remarkably consistent pattern: In the spring and fall, participants endorsed loyalty, authority, and purity significantly more strongly than during the summer and winter months. This pattern persisted throughout the entire ten-year observation period.

Why Would Moral Attitudes Change at All?

The study does not provide a definitive explanation for these seasonal fluctuations, but it discusses several possible mechanisms. One of the most interesting approaches comes from chronobiology—the field of research that examines how biological rhythms influence our behavior, physiology, and experience.

Chronobiology posits that nearly all organisms possess internal clocks. The best-known of these is the circadian rhythm, which spans approximately 24 hours and regulates sleep, hormone production, body temperature, and metabolism. Less well known, however, are so-called circannual rhythms—biological processes that vary over the course of a year.

These seasonal rhythms evolved as an adaptation to recurring changes in the environment. Daylight, temperature, food availability, and social activities vary considerably throughout the year. Even though modern societies partially compensate for these fluctuations through artificial light, air conditioning, and year-round food availability, many biological systems continue to respond to seasonal changes.

The Brain is Guided by Light

The most important pacemaker of the human organism is daylight. Light signals travel via the retina to the so-called suprachiasmatic nucleus in the hypothalamus, which is considered the body’s central internal clock. Numerous hormonal processes are controlled from there.

As the seasons change, both the length of the day and the intensity of natural light vary. Among other things, these changes influence the release of melatonin, which regulates the sleep-wake cycle, as well as, indirectly, various neurotransmitters such as serotonin and dopamine. Both of these neurotransmitters play an important role in mood, motivation, decision-making, and social interactions.

Chronobiological research has shown for years that immune function, metabolism, inflammatory processes, and even the activity of certain genes also change seasonally. Against this backdrop, it seems plausible that psychological processes, too, could be subject to seasonal fluctuations.

Hormones and Neurotransmitters: How Light Might Indirectly Influence Our Thinking

A central area of research in chronobiology focuses on how seasonal changes in daylight influence the release of hormones and neurotransmitters. Sunlight serves as our body’s most important timekeeper. Through specialized sensory cells in the retina, light stimuli reach the suprachiasmatic nucleus in the hypothalamus—the body’s “internal clock.” From there, numerous biological processes are coordinated that extend far beyond the sleep-wake cycle.

One of the best-known neurotransmitters is melatonin, which is produced primarily by the pineal gland in the dark. It signals to the body that it is time for rest and regeneration. In the summer, when the days are longer and more natural light reaches the retina, melatonin production begins later in the evening and is lower overall than during the darker winter months. This shifts not only sleep times but also numerous metabolic and hormonal processes.

The serotonin system is also closely linked to daylight. Serotonin is a neurotransmitter involved, among other things, in regulating mood, motivation, impulse control, and social behavior. Several studies show that the activity of the serotonergic system increases with sunlight exposure. This is considered one of the reasons why many people feel more energetic and emotionally balanced in the spring and summer. At the same time, serotonin is needed in the body as a precursor for the production of melatonin—the two systems are therefore closely linked biologically.

The stress hormone cortisol also follows a distinct circadian rhythm and, in addition, exhibits seasonal fluctuations. Normally, cortisol levels peak shortly after waking up and decline steadily throughout the day. Evidence from chronobiology suggests that this pattern also changes slightly over the course of the year. Since cortisol plays an important role in stress management, attention, and decision-making, there is ongoing discussion as to whether seasonal changes in the hormone might also contribute to changes in experience and behavior.

Added to this is the importance of vitamin D, which is produced in the skin under the influence of UV-B radiation. Although vitamin D is, strictly speaking, not a vitamin but a hormone-like substance, it influences numerous processes in the nervous system. Vitamin D receptors are found, among other places, in brain regions involved in emotion regulation. Low vitamin D levels are associated with various health problems as well as depressive symptoms. However, it has not yet been proven whether vitamin D directly influences seasonal changes in moral attitudes.

From a chronobiological perspective, therefore, it cannot be assumed that a single hormone or a specific neurotransmitter controls our moral thinking. More likely is a complex interplay of light, the body’s internal clock, hormonal changes, immune activity, metabolism, and emotional experience. The seasonal fluctuations in moral values observed in the UBC study could thus be an expression of a biological adaptation that occurs simultaneously on multiple levels. Which mechanisms have the greatest influence is the subject of current research.

Fear Could Play a Key Role

The researchers see the role of fear and uncertainty as a possible explanation for the seasonal changes in moral values. The University of British Columbia study showed a correlation between periods of higher anxiety levels and greater agreement with so-called binding moral values such as loyalty, authority, and purity.

From a psychological perspective, this connection makes sense: When people perceive uncertainty or threat, the need for guidance, stability, and social cohesion often increases. Clear rules, familiar structures, and belonging to a group can then be experienced as providing security.

This pattern could also make sense from an evolutionary biology perspective. In difficult environmental conditions, strong group cohesion was crucial for the survival of communities. The willingness to adhere to shared rules and support one’s own group could foster cooperation and protection.

However, the researchers emphasize that fear does not automatically determine moral attitudes. Moral thinking arises from a complex interplay of personality, culture, experiences, social influences, and biological factors. The seasonal changes could therefore be an expression of the interplay between the environment, the body’s internal clock, and emotional experience.

Evolutionary Roots of Seasonal Behaviors

This pattern also makes sense from the perspective of evolutionary psychology. Throughout most of human history, the seasons have meant significant differences in food availability, climate, and chances of survival. Communities had to repeatedly adapt to changing environmental conditions.

In times of greater uncertainty, stronger social cohesion may have improved survival. Loyalty to one’s own group, respect for shared rules, and adherence to social norms would have facilitated cooperation and reduced conflicts. Such mechanisms may still influence our behavior today—albeit to a lesser extent.

What is the Significance of these Findings?

If the results of further studies are confirmed, they could have far-reaching practical consequences. Moral convictions influence political attitudes, legal judgments, and social behavior. Previous research has already shown that moral values can, for example, influence a person’s willingness to get vaccinated during a pandemic or to comply with protective measures.

Seasonal changes could theoretically play a role in the legal system as well. People who place greater weight on binding values often judge rule violations more severely. However, whether this actually affects judicial decisions has not yet been sufficiently investigated.

An influence on voting decisions or social debates is also conceivable. If moral priorities shift slightly over the course of the year, political messages could be perceived differently depending on the season. Such considerations, however, remain hypotheses and require further scientific examination.

What the Study Does Not Show

Despite the intriguing results, caution is advised when interpreting them. The study reveals correlations but cannot prove causation. It does not prove that the seasons directly alter our moral thinking, nor that biological rhythms alone are responsible for the observed differences. Nor does the study imply that people generally act in a more “moral” or “immoral” manner in summer or winter. Rather, individual value priorities shift within an overall stable moral system. The observed differences are statistically significant but fall within a moderate range.

The study from the University of British Columbia provides fascinating evidence that our moral convictions may be more dynamic than previously assumed. In particular, loyalty, authority, and purity seem to be emphasized somewhat more in spring and fall than in summer or winter.

Chronobiology offers a plausible explanation for this. Seasonal changes in daylight, hormones, neurotransmitters, and emotional states could contribute to slight shifts in social evaluations as well. For now, these are primarily scientific hypotheses. Nevertheless, the findings impressively underscore that human behavior is not shaped solely by culture or personal beliefs, but may also be influenced by biological rhythms—rhythms that have accompanied us throughout our evolution and continue to shape our thoughts and actions to this day.