Jean Lamarck 1744-1829)
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School of Thought: "Lamarckianism" - A theory of biological evolution holding that species evolve by the inheritance of traits acquired or modified through the use or disuse of body parts. This philosophy is now held in disfavor.
Greatest Achievement: Lamarck was a botanist and invertebrate zoologist who formulated a theory of how evolution worked based on environmental shaping. While Lamarck's theory of Inheritance of Acquired Characteristics is now seen to be erroneous, his contributions to science in meteorology, botany, chemistry, geology, and paleontology make up for his errors. He published an impressive seven-volume work, Histoire naturelle des animaux sans vertèbres (Natural History of Animals without Backbones, 1815-1822).
Famous Texts: Philosophie Zoologique (1809)

While evolutionary theory had advocates dating all the way back to Anaximander of Greece, Lamarck was among the first to point to the fossil record and notice that fossils of various species showed that earlier forms were different from current forms of life. From this he concluded that environmental changes were responsible for physiological changes - that the environment shaped phylogeny. He argued that if a hunter species were led by scarcity to become better hunters (run faster) that the offspring of such animals would be born with stronger muscles - which would enhance their survivability. His theory was called the Inheritance of Acquired Caracteristics. Larmarck offered a normative/rhetorical argument that unless characteristics could be passed on to the next generation, all life forms were doomed to having to "start over" each generation.

Whenever rhetoric enters a scientific debate, watch out.

Lamarck accepted the view that animals in nature were arranged on one continuous scala naturae (natural scale). According to Lamarck, once nature formed life, the arrangement of all subsequent forms of life was the result of time and environment interacting with the organization of organic beings. From the simplest forms of life, more complex forms emerged naturally. These ideas were initially presented in Philosophie zoologique (Zoological Philosophy, 1809). Lamarck's final stab at evolutionary theory without genetics is presented in his multi-volume work on invertebrates. Here, Lamarck explains his scale of nature as being controlled by three biological laws:

Environmental influence on organ development
Change in body structure based on use and disuse of parts
and
The inheritance of acquired characteristics.