The Theory of Evolution from Humans to Polyps
At least since Aristotle, many authors had proposed refined classifications of animals. Anatomical studies had showed physiological similarities between species and had confirmed the animal status of the human body. Nonetheless, it was the common belief that God had conceived of each species and each creature. The similarities observed in different species demonstrate that God had used the similar organs to create different creatures. The idea eventually emerged that certain creatures, like the monkey, were closer to God (and humans) than others, like the amoeba,8 for instance.
The theory of evolution began to take form in Lamarck’s thoughts while he walked the corridors of the Museum of Natural History and wondered how the countless samples of species should be placed. He also benefited from the many projects undertaken by his colleagues at the museum and from the scientists with whom he was in contact, like Charles Bonnet of Geneva. Yet he is the only member of this community of brilliant biologists to have conceived of the possibility that there might be a history of the species. This required not only a great imagination and intelligence but also the courage of a warrior who jumps across a precipice. The difficulty was not only to imagine that such a history could have generated the human species, but also to accompany this hypothesis with arguments capable of making a theory of it that could be acceptable to his colleagues. He detailed this view in 1802 in Research on the Organism of Living Bodies. This volume presented the theory of evolution to the ordinary citizen. Beautifully written, it is still pleasing and surprising to read.
Lamarck’s pedagogy, developed in the first part of his work, is stimulating and effective. He starts from what is particular to humans and shows that it is possible to classify the species of animals according to what they do not possess. He conjectures that the simpler the organism, the more it is constitutionally distant from humans, the more it is ancient. The creatures lose their limbs, lay eggs instead of giving live birth. The regulation of the body temperature becomes less efficient when the animal is cold-blooded.â Insects do not have vertebrae. In moving backward, Lamarck helps the reader feel how life progressed in its development from matter, by becoming plants and then ever more complex creatures. This complexity gradually builds itself up, differentiating itself from what existed previously, by creating a growing variety of mechanisms. This progressive differentiation allows for the creation of the capacity to have a social life (ants and bees already have such a life), an affective life (manifest in mammals), and intellectual capacities (developed particularly in humans). The differentiation of organs, sensorimotor actions, and the capacity to think all make up the history of organisms. The organism, or the individual system, thus becomes the basic building block of the theory of evolution in the nineteenth century.
Lamarck’s theory follows, in its broad lines, the coherent and systemic vision of the universe proposed by Spinoza. Time does not alter this coherence, because nature did not, in its history, jump from the mollusks to humans to end up with crocodiles. This development is nonetheless not linear. For example, the dog’s keen sense of smell is more developed than that of humans.