Proposed that an organism could acquire an adaptation or trait that would make it more fit within its life time and it could then pass the trait to its offspring

Jean Baptiste Lamarck

Explanation:

Lamarck was naturalist who believed that physical changes (acquired characteristic) in organism could be transmitted to their offspring. So, for example, when environment changes, organism has to change its behavior to survive. If an organism begins to use an organ more than it did in the past, it would increase in its lifetime.

He often gave the example of a giraffe that stretched its neck for leaves and make it longer that way. He believed that giraffe's offspring would inherit the longer neck.