How did Lamarck propose that species change over time?

Lamarck proposed that species change over time through a process he called the "inheritance of acquired characteristics." According to his theory, an organism can acquire traits during its lifetime by using or not using certain body parts, and these changes are then passed on to its offspring. Lamarck's two main principles were "use and disuse" and "inheritance of acquired traits."

For example, Lamarck suggested that a giraffe's neck became long because its ancestors stretched their necks to reach leaves high up in trees. The constant stretching supposedly caused their necks to become slightly longer, and this change was then inherited by their descendants. Over many generations, this process resulted in the long-necked giraffes we see today.

While Lamarck's concept of inheritance of acquired traits was a step towards understanding evolution, it differs significantly from the modern theory of evolution by natural selection proposed by Charles Darwin. Lamarck's theory has since been largely discredited primarily because the mechanism he proposed is not supported by genetic evidence.