Jean-Baptiste Lamarck and Charles Darwin are two of the most influential figures in the history of biological thought. Their work, though separated by decades and fundamentally different in its conclusions, formed the bedrock for understanding how life on Earth changes over time. Before the 19th century, the dominant view held that species were fixed and unchanging. Both men contributed to the intellectual revolution that sought a natural explanation for the diversity of life, shifting the focus from static creation to a dynamic process of transformation. Their theories represent the most significant early attempts to explain the mechanism of species transformation, setting the stage for modern evolutionary biology.
Lamarck’s Evolutionary Framework
Lamarck’s theory, primarily set forth in his 1809 work Philosophie zoologique, provided the first comprehensive, secular model for species change. This framework was built upon two distinct laws. The first was the Law of Use and Disuse, which posited that an organ used frequently would develop and strengthen, while an unused organ would weaken and eventually disappear over generations. He suggested that environmental changes created new needs, prompting organisms to modify their habits and body structures.
The second law was the Inheritance of Acquired Characteristics, which stated that any physical changes gained during an organism’s lifetime could be passed on to its offspring. For example, the long neck of a giraffe was explained by generations of stretching to reach higher leaves, with the resulting elongation being inherited by the next generation. This model proposed that the organism’s interaction with its environment directly shaped its hereditary material.
The Shared Foundation: Change and Adaptation
Despite their differing mechanisms, Lamarck and Darwin shared a conceptual agreement that challenged the scientific orthodoxy of their time. Both agreed that the vast diversity of life was not fixed, but had undergone gradual change over immense spans of time.
They also concurred that environmental pressures were the ultimate driver of biological transformation. For both naturalists, organisms became adapted to their surroundings. This concept of environmental influence forcing change was a major departure from the static view of nature. They saw the history of life as a branching process, with species lines transforming in response to the world around them.
Darwin’s Lamarckian Inheritance Model: Pangenesis
A lesser-known aspect of Darwin’s work reveals his direct incorporation of Lamarckian thinking, particularly concerning the mechanism of heredity. Darwin accepted the inheritance of acquired characteristics as a factor in evolution, and he sought a physiological explanation for how it could occur. He presented his “provisional hypothesis” of Pangenesis in his 1868 work, The Variation of Animals and Plants Under Domestication.
Pangenesis proposed that every part of the body continually shed minute particles called “gemmules.” These gemmules circulated throughout the body and aggregated in the reproductive organs. Since gemmules were produced by somatic cells, any change to a body part—such as muscle strengthening or organ shrinking—would result in altered gemmules. These altered particles would then be passed on to the offspring, allowing the acquired trait to be inherited. Darwin used this hypothesis to provide a source of variation directly influenced by an organism’s lifetime experience, a concept distinct from his primary evolutionary driver.
The Critical Separation: Natural Selection
The most profound distinction between the two theories lies in the driving force and timing of change. Lamarck believed that variation arose in response to a felt need, where environmental necessity directly generated the adaptive change. Evolution was therefore a directed process initiated by the individual’s interaction with its surroundings.
Darwin’s theory of Natural Selection, however, proposed a fundamentally different sequence. Variation, he argued, arose randomly and spontaneously before any environmental pressure was applied. The environment did not direct the change but instead acted as an external filter, determining which pre-existing variations were beneficial for survival and reproduction. Individuals with advantageous traits would survive to pass on those traits at a higher rate. Ultimately, Darwin moved beyond Lamarck by shifting the source of evolutionary change from the individual’s directed effort to the non-random survival of randomly varying individuals.