Early Explanations for Evolution: Jean-Baptiste de Lamarck

Although Jean-Baptiste de Lamarck (1744-1829) contributed greatly to our understanding of the world he will most likely be best remembered for his 1809 theory of Inheritance of Acquired Characteristics. According to Jean-Baptiste, new traits arise in organisms because of the organism's inner want; newly developed traits can then be passed on to their descendants. Jean-Baptiste arrived at this conclusion based on observations of an ancestral population of short-necked giraffes and the observation that trees also appeared to get taller over time.

Depiction showing how giraffe neck evolved through aquired characteristics

Jean-Baptiste reasoned that as trees became taller short-necked giraffes had to stretch their necks to browse in trees. Once the necks of the short-necked giraffes became lengthened this newly acquired characteristic would be passed on to their decedents. Over time, as trees grew taller and taller, this process continued until giraffes no longer had to stretch their necks to browse in the trees. Based on the evidence available at the time Lamark's theory seemed logical and was accepted as a driving force of evolution. 

Considering the information available at the time, Lamarck's theory seemed logical and was accepted by some as a viable mechanism for evolution. Lamark's theory would remain the best explanation for evolution for many decades and would only be discredited after it was shown that genes, the agent responsible for all organism's characteristics, could not be voluntarily changed by an organism during its lifetime.