Why did Lamarck believe that small changes could lead to major differences among species over time?

Jean-Baptiste Lamarck believed that major differences among species arose from the cumulative effect of small, adaptive changes occurring over vast periods of time. His theory was built on the premise that environmental changes create new needs (besoins) for an organism, prompting it to adopt new habits.12

These habits led to the increased use or disuse of specific organs, resulting in physical strengthening or weakening of those parts. Lamarck proposed that these material alterations—acquired characteristics—were then transmitted to the organism's offspring. By repeating these behaviors across generations, these minor, incremental modifications gradually transformed the species.132

Lamarck viewed this process as one of two primary forces driving organic development, the other being an inherent "power of life" that pushed organisms toward increasing complexity. While his specific mechanism of inheritance was later discredited by modern genetics, Lamarck remains significant as the first naturalist to systematically argue that the long-term operation of such processes could account for the diversity of life on Earth.13