It is safe to say that the pursuit of happiness—a phrase penned by the Founding Fathers in the Declaration of Independence—has served as a primary ambition for many Americans throughout the nation’s history. It was soon after World War I when—as I posit in Happiness in America: A Cultural History—the modern concept of happiness was born, part of the broad attempt to apply scientific principles to mental health. Happiness became an ever-louder part of the national conversation over the past century, riding on the greater interest in psychology and the expansion of that field, especially as related to personality.

In his 1926 Understanding Ourselves: The Fine Art of Happiness, for example, Harold Dearden, a physician, showed how individuals could become happier through an acquaintance with the principles of modern psychology. Since it was the nervous system that regulated both physical and psychical well-being, Dearden maintained in the scientific parlance of the times, one’s level of happiness could be managed through inner fortitude and the power of reason. Fears and worries, as well as harmful habits, instincts, impulses, and obsessions, could be eliminated by learning “the fine art of happiness,” he argued, with logic and rationalism the means by which to keep the more primitive goings-on of the mind at bay.

Louis Berg also believed that people could follow certain principles to increase one’s chances to be happy in life. Pursuing good “mental hygiene” was analogous to pursuing good physical health, he, like many in the medical field at the time, thought, with the former heavily reliant on maintaining a positive attitude and developing what was termed a “balanced” personality.

Proponents of mental hygiene—the movement founded by Clifford W. Beers in the early 20th century—argued that happiness was largely a result of how individuals related to society. “Social consciousness is the core of adjustment and happiness,” Berg stated in his 1933 textbook The Human Personality, with extroverts far more likely to be happy than those who shied away from interaction with others.

Happiness continued to gain traction in the field of psychology after World War II. Americans too often lived in the past and future, R.M. MacIver argued in his 1955 The Pursuit of Happiness: A Philosophy for Modern Living, with only living in the “momentary now” leading to the type of happiness that so many were seeking. Anticipating the kind of thinking in the field that was a few decades away—notably the concept of “flow”—MacIver recognized that time tended to stand still or disappear when one was truly happy, with only the present able to offer that level of transcendence.

Equally impressive, he was keenly aware of the individualization of happiness, i.e., that it was a different experience for everyone, this too making him ahead of his time. “Happiness is the resonance of the whole being as it moves towards that which fulfills it,” MacIver poetically wrote, nicely boiling down the abstract concept into “the harmony within you.”

By the 1980s, however, advances in genetics were making psychologists rethink the dynamics of happiness. Unhappiness had a strong genetic component while happiness did not, according to a study led by Edward Diener of the University of Illinois, implying that the former was mostly a function of nature and the other mostly of nurture.

The research also suggested that happiness and unhappiness were thus not, as logic dictated, opposite or inverse emotions; rather, the two appeared to operate independently. Ridding oneself of some unhappiness in life therefore did not mean that one would become any happier, a counterintuitive notion that threw a monkey wrench into much of the out-with-the-bad, in-with-the-good brand of self-help being cast about at the time. The good news was that, at least according to this research, happiness was not genetically preordained, and could thus be achieved by those who were determined or lucky enough to find it.

In the 1990s, serious scholarly inquiry into the psychology of happiness was leading to new insights. In their article “Who Is Happy?” published in Psychological Science in May 1996, for example, Diener and David Myers argued that happiness was spread out evenly over the course of a lifetime—something not commonly believed. The pair also found four personal traits to be associated with high levels of happiness: extroversion, optimism, high self-esteem, and the feeling that one was in control of one’s life.

Advancements in neuroscience and the completion of the Human Genome Project in 2003 each had a direct effect on the trajectory of happiness in America. Individuals had what could be considered a happiness gene, scientists were concluding, making one’s relative state of happiness or unhappiness more a matter of biology than psychology. MRI scans plainly revealed when a person was happy, with that part of his or her brain lighting up like a Christmas tree. Altering one’s happiness gene could one day be possible, more scientists were beginning to think, with such an approach envisioned as being far more effective than all the how-tos grounded in some kind of attitudinal or behavioral modification put together.

Unless or until our emotions can be genetically programmed, however, many of us will no doubt continue our unalienable right to pursue happiness.