How Do Sunlight, Happiness, And IQ Relate To One Another?

Researcher Satoshi Kanazawa discusses how exposure to sunlight affects happiness levels of low and high-IQ individuals.

By Mark Travers, Ph.D. | March 26, 2022

A new study published in the Journal of Cognition and Emotion investigates how sunlight relates to a person's happiness, and how this relationship may be influenced by an unlikely source: intelligence, or IQ.

I recently spoke to researcher Satoshi Kanazawa, one of the authors of the paper from the London School of Economics and Political Science, to better understand these effects. Here is a summary of our conversation.

What inspired you to investigate the relationship between sunshine, happiness levels, and intelligence, how did you study it, and what did you find?

When I entered the field of positive psychology and happiness research 10 years ago, I was struck by the complete absence of general theory in the field. Positive psychologists have done a great job of discovering a large number of correlates of happiness — who is happier than whom, when and under what circumstances. But there was no general theory that could explain why some people were happier than others.

I was trained as a theorist and I believe that 'why' is the most important question in science. So I set out to provide the why in positive psychology.

I teamed up with my fellow evolutionary psychologist, Professor Norman P. Li (Singapore Management University), to formulate an evolutionary psychological theory of happiness, which we call the Savanna Theory of Happiness.

The theory proposes that, because the human brain is evolutionarily designed to perceive the current environment as if it were still the ancestral environment — roughly the Pleistocene Epoch about 2.6M to 12K years ago — it follows that our current levels of happiness are influenced not only by the modern consequences of the current situation in which we find ourselves but also by their ancestral consequences — what the current situation would have meant in the ancestral environment.

Further, because what we call general intelligence today originally evolved as a psychological mechanism to solve evolutionarily novel adaptive problems that our ancestors did not routinely encounter, it follows that the effect of such ancestral consequences of the current situation on happiness is stronger among less intelligent individuals than among more intelligent individuals.

Along the way, we welcomed Professor Li’s protégé, Dr. Jose C. Yong (Northumbria University), to the team, and the three of us have been testing the Savanna Theory of Happiness, which is one of the first general theories of happiness, in various domains.

We have so far discovered that being an ethnic minority reduces your happiness, because seeing others of different appearance, language, culture, and practice almost always signified danger in the ancestral environment, because it usually happened under conditions of war, conquest, capture, and slavery; population density reduces happiness — ruralites are happier than urbanites — because our ancestors lived in very sparsely populated areas, and crowdedness meant impending breakdown of social order based on personal ties and impending resource shortage; and socializing with friends increases happiness, because our ancestors were a physically vulnerable species living in harsh environments, and ostracism was tantamount to a death sentence.

In every case, the effect of ancestral consequences on happiness was stronger among less intelligent individuals than among more intelligent individuals. In fact, the effect of intelligence on the association between socializing with friends and happiness was so strong that more intelligent individuals actually experience less happiness if they socialize with friends more.

In the current paper, we focus on another current situation that has ancestral consequences that are different from current consequences: sunlight. Until the domestication of fire, our ancestors did not have any artificial means of illumination; the sun and the moon (when it was out) were the only natural sources of illumination. Thus darkness always represented potential danger of predation and attack, and thus being in the dark should make us, even today, more anxious, fearful, and less happy. Further, the negative effect of darkness on happiness should be stronger among less intelligent individuals than among more intelligent individuals.

That is exactly what we find. Our analysis of data from the National Longitudinal Study of Adolescent to Adult Health (Add Health) shows that even net of all other climate factors and demographic background, the annual number of sunshine hours increases happiness, but the effect of sunshine hours on happiness is significantly stronger among less intelligent individuals. The more sunshine you are exposed to, the happier you are, especially if you are less intelligent.

How does your study define a high versus a low intelligence individual?

It doesn’t. Intelligence is a continuous variable, like height. For convenience, we can talk about “tall people” and “short people,” but there is no clear line of demarcation between two kinds of people. It doesn’t make sense to say “If you are 5’10 or above, you are tall; if you are less than 5’10, you are short.” In fact, two kinds of people don’t exist. Everyone is more or less taller or shorter than everyone else. It’s a continuum without any clear line of demarcation.

Intelligence is exactly like that. For convenience, we talk about “more intelligent people” and “less intelligent people,” but there is no clear line of demarcation, and the two kinds of people do not exist. Everyone is more or less intelligent than everyone else. For graphic purposes, we sometimes use an arbitrary cutoff point so that we can show neat charts in our paper, but there is no significance to any given cutoff point. They are all arbitrary.

Is one response to sunlight inherently ‘better’ than the other?

“Better” is a word that I never use as a scientist. Science does not make value judgments. Nothing is “better” or “worse” than anything else. Instead, I can talk about a “natural” or evolutionarily designed response, and an “unnatural” or not evolutionarily designed response. The “natural” response designed by evolution is to feel safe, secure, and happy when exposed to sunlight, because you are in less danger of predation and attack in greater sunlight. The “unnatural” response, not designed by evolution, is not to feel safe, secure, and happy when exposed to darkness, because, in darkness, we can simply turn on the (evolutionarily novel) flashlight.

In general, more intelligent individuals have “unnatural” preferences and values in all domains of life, and this is just one example of such. But neither “natural” nor “unnatural” is better or worse. To say what is natural is better is to commit the naturalistic fallacy. If what is natural is good, then murder, rape, and war are all good.

Besides the evolutionary-related reasons outlined in your paper, what are some of the practical reasons that exposure to more sunlight is able to make people happier?

I can’t think of any. Everybody takes it for granted that sunshine makes people happy, because it does. And I believe the reason it does is the evolutionary reason that we explain in our paper. We have felt this way for more than two million years, and that’s why we take it for granted.

To what extent (if any) can a lack of happiness be detrimental to a person’s physical and mental well-being?

“Mental well-being” is happiness. If, by “physical well-being,” you mean general health, then, yes, all the available data show that health and happiness are significantly positively correlated — healthier people are happier. However, it does not necessarily mean that health affects happiness. It’s more likely that the causal arrow goes the other way around — happier people become or stay healthier.

Happiness is a higher-order (second-order) adaptation. Happiness does not directly increase your reproductive success, but happiness increases the chances that you engage in activities that increase your reproductive success, like getting married, staying married, having children, having friends, maintaining alliances, etc.

Taking care of your physical well-being and staying healthy is another consequence of being happy. Happier people are more likely to engage in activities that increase your health, and less likely to engage in activities that decrease your health. That’s why happier people are healthier. Your baseline level of happiness is largely determined genetically, so very little can drastically change your baseline. Instead, happiness changes a lot of other things in your life, including health.

What advice do you have for people that live in climates with little sun or are experiencing Seasonal Affective Disorder (SAD)? In what ways can they pursue a happier life?

Giving advice is something I don’t do as a scientist. In fact, as a scientist, I don’t do anything, except for one: explain. That’s all I ever do as a scientist. I don’t do anything else, including giving advice to people on how to pursue a happier life.

As it turns out, however, there is already a very effective cure for Seasonal Affective Disorder (SAD) that is perfectly consistent with our findings: light therapy. You can reduce symptoms of SAD by deliberately being exposed to artificial light. (It’s probably better if it’s natural light, but one can’t control sunshine as easily as one can control artificial sources of light.) Another finding from previous research that is consistent with our theory is that less intelligent individuals are more likely to experience SAD.

Do you have plans for follow-up research?

We already have another paper forthcoming on the Savanna Theory of Happiness. In our next paper, entitled “When Intelligence Hurts and Ignorance is Bliss: Global Pandemic as an Evolutionarily Novel Threat to Happiness,” forthcoming in the Journal of Personality, we expand our theory and discuss entities and situations that are entirely evolutionarily novel and have no ancestral analogs. Once again, because general intelligence originally evolved to solve evolutionarily novel adaptive problems, more intelligent individuals are better able to comprehend evolutionarily novel entities and situations and their consequences for happiness. In the forthcoming paper, we use the COVID-19 global pandemic as an example of an evolutionarily novel situation that has no ancestral analog. Because pandemics and epidemics require large populations — at least half a million, by one estimate — epidemic diseases did not exist in the ancestral environment. Thus more intelligent individuals are more likely to comprehend epidemics and pandemics, and, since COVID-19 has very few positive consequences that make us happy and countless negative consequences that make us unhappy, the current pandemic should make more intelligent individuals less happy relative to less intelligent individuals.

That is exactly what we find. With two separate large, prospectively longitudinal population samples from the United Kingdom — this is the first time we tested the Savanna Theory of Happiness outside of the United States — we show that, while more intelligent individuals are in general happier than less intelligent individuals throughout their lives, there was a reversal in the association between intelligence and happiness during COVID-19. In 2020, for the first time in their lives, less intelligent individuals were happier than more intelligent individuals were. In fact, less intelligent individuals became happier after the start of the pandemic, while more intelligent individuals become less happy.

Where would you like to see research on happiness, intelligence, and sunshine go in the future?

We plan to continue our research on the Savanna Theory of Happiness, by subjecting it to further empirical tests. So we plan to continue our work on happiness and intelligence. However, we are unlikely to continue our work on sunshine. It was just one factor that has divergent consequences in the current and ancestral environment, so we used it as another example of factors that can explain modern happiness. We are likely to search for other similar factors, instead of going back to sunshine.