Why did some 19th-century scientists support neo-Lamarckism?

In the late 19th century, some scientists and thinkers supported neo-Lamarckism as an alternative to Darwin’s theory of natural selection, largely because they found it difficult to explain complex biological phenomena through selection alone.1

The primary reasons for this support included:

• Explaining Adaptation: Neo-Lamarckians believed that the environment acted directly on organic structures, providing a more intuitive explanation for how organisms adapted to their specific ways of life than the perceived randomness of natural selection.1
• Use and Disuse: Adherents maintained that the use or disuse of organs directly influenced their development or obliteration, a mechanism they felt was essential for understanding evolutionary change.1
• Instincts and Behavior: Some researchers, including psychologists, turned to Lamarck’s doctrine because they struggled to explain the inheritance of coordinated reactions and complex instincts without assuming that nervous reactions acquired during an individual's life could be passed down.2
• Conceptual Appeal: The theory resonated with those who saw a resemblance between heredity and memory, leading some writers and thinkers to favor it over the purely mechanical processes proposed by Darwinists.2