Charles Darwin’s publication of On the Origin of Species in 1859 marked a turning point for the nascent field of psychology, which was primarily rooted in philosophy and focused on the structure of consciousness. Before Darwin, the examination of the mind largely involved introspection, aiming to break down mental processes into their elemental components, a structuralist approach often associated with German labs. Darwin’s theory of evolution by natural selection provided an entirely new, empirical framework for understanding the human mind by placing it squarely within the biological world. His work introduced the idea that mental traits, like physical ones, were products of adaptation to the environment, shifting the focus of psychological inquiry from “what the mind is made of” to “what the mind is for.” This moved the study of the mind away from philosophical speculation and toward an objective, scientific discipline concerned with function and observable behavior.
The Shift to Function and Adaptation
Darwin’s concept of natural selection suggested that mental processes must also possess survival value, as traits that enhance survival and reproduction are passed down. This idea led early American psychologists, most notably William James, to develop the school of thought known as Functionalism. Functionalists were concerned with the utility and purpose of consciousness, viewing mental activities such as memory, learning, and perception as tools that help an organism adjust to a constantly changing environment.
Functionalists began asking how mental processes operate in a dynamic, real-world context, focusing on the actions and consequences of behavior. For instance, problem-solving was no longer seen as a mere collection of sensations but rather as an adaptive process designed to overcome environmental obstacles. This evolutionary focus on the utility of the mind established a pragmatic tradition in psychology, laying the groundwork for later movements like behaviorism.
Continuity of Mind: Comparative Psychology
The theory of evolution inherently established a principle of phylogenetic continuity, suggesting that humans share a common ancestry with other species, and therefore, mental processes are not unique to people. This idea provided a scientific justification for studying animal behavior as a means to understand human psychology, thus giving rise to comparative psychology.
Early figures like George Romanes began publishing works that cataloged mental abilities across the animal kingdom, though his methods were sometimes anecdotal. Later, C. Lloyd Morgan introduced a more rigorous, objective approach, urging researchers to avoid anthropomorphism and interpret animal actions at the lowest psychological level possible. This methodological shift toward objective observation of behavior, rather than relying on assumed animal introspection, was a fundamental step in making psychology a truly empirical science.
The Scientific Study of Individual Differences
Natural selection requires the existence of variation, meaning individuals within a species must differ for some traits to be favored over others. Darwin’s emphasis on this individual variation directly inspired the development of differential psychology, which focuses on measuring and studying the psychological differences between people. The most influential figure in this area was Darwin’s cousin, Sir Francis Galton, who recognized that if physical traits were inherited, so too might be mental abilities.
Galton pioneered the application of statistical methods to psychological questions, developing techniques like correlation and regression to quantify human traits. His work focused on measuring reaction times, sensory acuity, and intellectual ability, establishing the first systematic approach to mental testing. Galton’s interest in the inheritance of “genius” led to his foundational work in psychometrics, creating the tools and statistical logic necessary to study intelligence and personality.
The Evolutionary Basis of Emotion
Darwin also made a direct contribution to a core psychological topic with the publication of The Expression of the Emotions in Man and Animals in 1872. In this work, he argued that emotional expressions, such as smiling, frowning, or baring teeth in anger, are not arbitrary human conventions but rather inherited, biologically functional traits. He proposed that many human expressions are evolutionary remnants of actions that were once directly useful for survival in our ancestors.
Darwin’s detailed cross-cultural observations demonstrated the universality of certain expressions, suggesting a shared evolutionary heritage across all human races. For example, he posited that the expression of fear, characterized by widened eyes, serves the adaptive function of increasing the visual field and allowing more light to reach the retina. By framing emotions and their outward displays as adaptive signals, Darwin provided the first scientific explanation for their existence, formalizing the study of emotion as a biological and psychological inquiry.