Which scientist developed a theory suggesting organisms could pass characteristics through an "unknown nervous fluid"?

The concept of characteristics being passed through an "unknown nervous fluid" is attributed to Jean-Baptiste Lamarck, who proposed an early theory of evolution known as Lamarckism. This theory posited that organisms could acquire traits during their lifetime based on their experiences or behaviors and then pass these acquired traits to their offspring. Lamarck believed that this "nervous fluid" was instrumental in the process of adaptation, allowing species to modify themselves in response to their environment over generations. His ideas laid foundational thoughts on evolution, although they were later challenged and refined by Darwin's theory of natural selection. Lamarck's emphasis on the role of the environment and acquired characteristics makes his contributions particularly significant in the study of evolutionary biology.