The profession of psychology dates back nearly 150 years. Throughout that time, many psychologists and other professionals have made significant contributions to the field. And while most casual psychology students know primarily about experimental psychologists, other kinds of psychologists have also made their mark on the profession.

Here we walk through a few of the many hundreds of historical moments in psychology.

Many of the earliest and most famous psychologists were academics, studying the in what we now call experimental psychology. Experimental psychology is focused on the design and implementation of scientific research through carefully-designed experiments to study human behavior and the mind. It is the foundation of all the different psychology specialties that followed.

Psychology might not have ever been the science that it is today were it not German scientist, physician, and philosopher Wilhelm Wundt. Born in 1832, he founded the first psychology laboratory at the University of Leipzig in 1879. Along with a slew of graduate students, Wundt conducted many of the first experiments into human behavior in trying to unravel the mysteries of the mind. This marks the official start of psychology as an independent science of individual human behavior and the mind.

His laboratory was wildly successful in churning out new psychologists to help in the expansion of this new field. According to Wikipedia, some of his more famous American students include: James McKeen Cattell, the first professor of psychology in the United States; G. Stanley Hall, the father of both child and adolescent psychology, and Edward Bradford Titchener, the developer of a theory of the mind called structuralism.

Unfortunately, due to language differences, some of Wundt’s work was misunderstood and led to many misconceptions about his beliefs and theories. Some of these were propagated by his own students, especially Titchener.

William James earned his M.D. degree in 1869 from Harvard, but he never practiced medicine. Instead he taught at Harvard, beginning 1873 first in physiology, then offering the first course in “physiological psychology” — psychology’s initial name in the U.S. The first doctoral degree in psychology was granted to Wundt’s student, G. Stanley Hall, in 1878 at Harvard. Harvard also housed the country’s first psychology laboratory (image below).

James is known for a number of theories in psychology, including the theory of self, the James-Lange theory of emotion, pragmatic theory of truth, and the two-stage model of free will. His theory of self suggested that individuals divide themselves into two categories, Me and I. “Me” is further divided into the material self, the social self, and the spiritual self, while the “I” James considered to be pure ego — what we today might think of as the soul (or consciousness).

The James-Lange theory of emotion suggests that all emotion is simply the mind’s reaction to some stimulus in the environment. That reaction create a physiological sensation, that we in turn label an emotion or feeling. James also contributed significantly to the philosophy of religion.

Edward Thorndike, a native of Massachusetts, studied at Harvard under William James. He received his doctorate from Columbia University in 1898, working under the supervision of James McKeen Cattell, best known for his work in psychometrics. Thorndike’s work focused on the development of the field of educational psychology — the study of how people learn in order to understand and develop better educational materials and methods for teaching.

Despite often being called the father of educational psychology, Thorndike spent a significant amount of time in the lab. He designed experiments with animals to better understand how they learned. The most famous of these experimental methods was through using puzzle boxes. In a basic design of a puzzle box, an animal — Thorndike preferred cats — is placed into it and needs to press a lever in order to open a door that will let them out of the box.

Giving rise to more pop psychology memes than any other person on this list, Sigmund Freud was an Austrian born physician who graduated with his MD in 1881. As a part of his studies, he worked for six years in a physiology lab, studying the brains of humans and other mammals, which likely helped foster his lifelong fascination and study of the mind. After working in Vienna’s hospital for a few years, he changed direction and went into private practice in 1886 specializing in the care and treatment of “nervous disorders.”

By the late 1890s, he was referring to his work as “psychoanalysis” and began publishing papers and books on his work. As more colleagues read his work, he started to develop a following. In the early 1900s, he began to meet with his followers, which culminated in the 1908 meet of the first International Psychoanalytic Congress. Alfred Adler and Carl Jung were famous students of Freud’s original theories, but left his circle as their views started to diverge from Freud’s own.

Freud led an illustrious life in his role as the father of psychoanalytic theory. He and his family fled Austria for London in 1938 with the rise of the Nazi Party and to escape from persecution. He died only a year later of cancer.

B.F. Skinner (the B.F. stands for Burrhus Frederic) is an American psychologist who is best known for his work on operant conditioning, a form of behavior modification that helps explain and alter behaviors. He called his form of behaviorism “radical behaviorism.” He received his doctorate from Harvard in 1931, where he went on to spend the majority of his professional career.

Skinner is known for his focus on reliable, replicable experimental designs in the study of behavior. In order to create such designs, he created a number of experimental inventions, including the operant conditioning chamber — known more commonly as a “Skinner box.” By manipulating either a lever or a disk in a way, an animal in the box (most often a rat or pigeon) could receive a reward. This led to the creation of theories about ideal reward reinforcement schedules. His theories of behavior reinforcement led to the creation of token economies — forms of behavior modification still in use today (often used with children for chores, but also in psychiatric inpatient settings).

Studying under William James and Hugo Münsterberg at Harvard, Mary Whiton Calkins is best known for her studies and writings in self-psychology, a new theory building upon other schools of thought related to the study of the self. Having a strong interest in experimentation as well, she thought it was important any such study of self-psychology also be born out in scientific research. Harvard did not confer degrees to women. So despite completing all of the necessary coursework and requirements for a doctoral degree in psychology, she never received one. (She refused an equivalent doctoral degree offered by Harvard’s associated women’s college, Radcliffe, in 1902.)

Her theories were not always well-accepted by her peers at the time. She ended up publishing four books and over a hundred papers in psychology and philosophy over the course of her career. In 1905 she was elected president of the American Psychological Association and she woman to establish her own psychology lab in the U.S.

While this list is dominated by Americans, French psychologist Alfred Binet deserves a mention. He is the man partially responsible for the IQ test — a test designed to measure overall intelligence, captured in the form of an Intelligence Quotient (IQ) score.

Binet studied law but also physiology, and after getting his law degree in 1878, he went to work at a neurological clinic in Paris in the 1880s. He then had a long career as a researcher and director of the Sorbonne. Throughout his career, he published over 200 books and articles on a wide variety of topics.

Working with a medical student, Theodore Simon, in 1905 Binet developed the first attempt to objectively measure intelligence in children, from ages 3 to 13. The purpose of this effort, called the Binet-Simon Scale, was to help in understanding the best way to educate all children, regardless of their abilities. When it was brought to the U.S. in 1916, it took on a different name reflecting the institution — Stanford University — of the test’s supporting psychologist, Lewis Terman. Although no longer actively used, it was the basis for modern IQ tests, known as the Wechsler intelligence scales.

Like many people associated with the history of psychology, Ivan Pavlov wasn’t a psychologist, but rather a Russian physiologist who quit the priesthood to study science. He developed the theory of classical conditioning to help explain behavior, demonstrating the external stimuli can have a direct influence in a behavioral response. This conditioned reflex, or Pavlovian response, is a core tenet of behavioral psychology. He came to his theory through experimentation with dogs and examining their anticipatory salivation when presented with the possibility of food in conjunction with the ringing of a bell. Eventually you could you produce the salivation by ringing the bell alone, regardless of whether food was present.

He eventually won a Nobel prize for his work.

Harry Harlow is an American psychologist who studied under Lewis Terman at Stanford University and received his Ph.D. in 1930. He’s best known for his “monkey studies,” because he studied the behavior of monkeys in a laboratory environment while at the University of Wisconsin-Madison. His research demonstrated that baby monkeys needed more than mere sustenance than to thrive. In order to thrive psychological and emotionally, the monkeys needed “contact comfort.”

This finding supported his belief that human babies needed similar contact from their mothers in order to grow and thrive. These findings contradicted traditional child rearing advice of the day, which suggested that parents should avoid bodily contact with their children. It was an important breakthrough that continues to influence parenting styles to this day.

Image credits: Wikimedia Commons, U.S. Library of Congress, and others