Which theory was put forth by Jean-Baptiste Lamarck?

Jean-Baptiste Lamarck is most well-known for his theory that emphasized the idea of the "use and disuse" of traits. This concept suggests that organisms can develop or lose characteristics based on their usage during their lifetime. For example, a giraffe's long neck evolved because its ancestors stretched to reach higher foliage; the constant use of this trait resulted in its enhancement over generations. This idea laid the groundwork for early evolutionary thought, proposing that organisms could adapt to their environments through their activities and that these adaptations could be passed on to their offspring.

Lamarck's theory, though later eclipsed by Darwin's theory of evolution via natural selection, was significant in illustrating a process whereby species could change over time and towards adaptation, making it a notable historical concept in biology and understanding evolution.