- In the years after his service during the French military campaign in Germany in the 1760s, Jean-Baptiste Lamarck studied medicine and botany. This led to a job at the Jardin des Plantes royal botanical gardens, which was soon reorganized into the Musée National d'Histoire Naturelle. At the museum, Lamarck became the professor of invertebrates, where he coined the term "invertebrate" and succeeded in advancing classification of invertebrate animals. During this time, Lamarck published a variety of work on invertebrates, paleontology, physics and even meteorology, with his first writings on evolution finally coming to publication in the early 19th century.
- In his book "Philosophie zoologique," Lamarck detailed his theory of evolution, which stated that organisms constantly evolved with each generation. He supplemented this claim by declaring two laws for evolution. The first law is that environmental change causes an organism to behave differently, thus resulting in use or lack of use of a given organ. Increased use causes said organ to grow while lack of uses causes the organ to shrink--a change that would occur over several generations. Lamarck's second law dictated that these changes were traits that were inherited from a parent organism.
- Both Darwin and Lamarck believed that organisms evolve due to environmental change, and both even used the same evidence for their theories, like the variety of organisms that occur through controlled breeding and the presence of vestigial organs in animals. Darwin even accepted Lamarck's belief that such changes could be inherited.
However, Darwin hypothesized that natural selection was responsible for the proliferation of certain characteristics, while Lamark did not find natural selection to be very important, as he did not believe in the possibility of extinction. Rather, he believed in constant evolution into more complex forms, and that species only vanished because they had evolved into something else. As for a reason why simpler organisms like protists continue to exist, Lamarck attributed their presence to spontaneous generation. - Lamarck's theory prove controversial, and there were various attempts to discredit the naturalist and his work, including from his own museum colleague, Georges Cuvier. This controversy not only stemmed from scientific disagreement, but also the implication that this evolution is occurring naturally and not through divine power.
In the years following Lamarck's death, scientists did not know how genetic inheritance worked. Thus, Lamarck's theory of inheritance seemed a sound theory for evolution until the work of Gregor Mendel surfaced and proved Lamark's theory to be in conflict. - While his theories were discredited, Jean-Baptiste Lamarck is significant for being the first naturalist to declare a fully thought-out theory of evolution while his contemporaries simply suggested the possibility of natural change. While Charles Darwin ultimately receives credit for his contributions to the theory of evolution, he cited Lamarck as an important figure for drawing attention to the subject
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