On August 1, 1744, Lamarck was born in an impoverished aristocratic family in southern France. His father sent him to a seminary in the hope of joining the priesthood. However, Lamarck left school to join French army. Five years later, he was discharged from army following injury. Although earning a living in a bank was his daily job, botany and natural sciences occupied his spare time. Because of accomplishments in botany, several top French naturalists highly appreciated him. The famous Buffon was one of them.
Lamarck published a three-volume monumental work on botany and became a member of the French Academy of Sciences under Buffon's help. However, the renowned work of Lamarck began after his fifties. Since scientific research institution was reorganized during the French revolution, Lamarck was assigned to study the invertebrates, a field that is almost neglected by everyone. His views were scorned by government and the church, poor relationships with coworkers were another reason.
Differences among organisms was dominated by combination of vital force and adaptive force.
Invertebrate fossils look very similar to extant species. If they were arranged chronologically from oldest to most recent, a continuous linear lineage was formed. Every organism possesses a latent vital force that allows them to spontaneously evolve from simple to sophisticated. The earliest life was undeveloped and primitive. Then they are more and more complex until the ultimate creatures, human.
The adaptive force reconstructs organisms in order to create new balance with changed environment. Thus, there are notable variations even among the same species on different surroundings. To reduce their water resistance, the submerged leaves in water buttercup are thin and branching. Floating leaves are typically larger and more rounded with a waxy coating, but the edges have small cracks.
Same phenomenon occurs in animals. When nervous system detects changes in the environment, it prompts animals to make corresponding behaviors to adapt. Certain organs and new parts derived from vital force will be used more frequently to result in enhancement. Non frequently used organs will gradually degenerate or even disappear. The development and degradation should be inherited by descendants. They accumulated over several generations to cause stable new trait. Changing is so slow that it is not visible to humans during their limited lifetime. This is sometimes referred to as the inheritance of acquired traits.
Almost all textbooks utilize the example of giraffe to illustrate use and disuse. Ancestors of giraffes strove to extend their short necks to eat tender leaves at the tops of trees. The neck lengthened and passed down to their progeny, who underwent a similar procedure to evolve into modern giraffes. Anteater was another tool Lamarck used to depict atrophied organs. All vertebrates originally possessed teeth in both jaws. Since these teeth were useless for eating ants, they disappeared in anteater. Lamarck also speculated that domesticated species transformed from wild species. Their differences were caused by differences between artificial and wild environment.