10.2 Lamarck’s Theory

10.2 Lamarck’s Theory

Lamarck incorporated two ideas into his theory of evolution, in his day considered to be generally true:

1. Use and disuse –Individuals lose characteristics they do not require (or use) and develop characteristics that are useful.
2. Inheritance of acquired traits –Individuals inherit the traits of their ancestors.

In essence, a change in the environment brings about change in “needs” (besoins), resulting in change in behaviour, bringing change in organ usage and development, bringing change in form over time -and thus the gradual transmutation of the species.

However, as historians of science such as Michael Ghiselin and Stephen Jay Gould have pointed out, none of these views were original to Lamarck. On the contrary, Lamarck’s contribution was a systematic theoretical framework for understanding evolution. He saw evolution as comprising two processes;

1. Le pouvoir de la vie (a complexifying force, in which the natural, alchemical movements of fluids would etch out organs from tissues, leading to ever more complex construction regardless of the organ’s use or disuse. This would drive organisms from simple to complex forms.
2. L’influence des circonstances (an adaptive force), in which the use and disuse of characters led organisms to become more adapted to their environment. This would take organisms sideways off the path from simple to complex, specialising them for their environment.