Lamarckism

A discredited theory of evolution developed by French biologist Jean-Baptiste Pierre Antoine de Monet, Chevalier de Lamarck in the 19th century. Lamarckism holds that traits acquired (or diminished) during the lifetime of an organism can be passed to its offspring. Lamarck based his on two observations considered to be true in his day:

1. Use and disuse - Individuals lose characteristics they do not require and develop those which are useful.
2. Inheritance of acquired traits - Individuals inherit the acquired traits of their ancestors.

Examples include: the stretching by giraffes to reach leaves leads to offspring with longer necks; strengthening of muscles in a blacksmith's arm leads to sons with like muscular development.

With this in mind, Lamarck developed two laws:

1. In every animal which has not passed the limit of its development, a more frequent and continuous use of any organ gradually strengthens, develops and enlarges that organ, and gives it a power proportional to the length of time it has been so used; while the permanent disuse of any organ imperceptibly weakens and deteriorates it, and progressively diminishes its functional capacity, until it finally disappears.
2. All the acquisitions or losses wrought by nature on individuals, through the influence of the environment in which their race has long been placed, and hence through the influence of the predominant use or permanent disuse of any organ; all these are preserved by reproduction to the new individuals which arise, provided that the acquired modifications are common to both sexes, or at least to the individuals which produce the young

Thus, a change in environment brings about change in "needs" (besoins), brings change in behavior, brings change in organ usage and development, brings change in form over time — and thus transmutation of the species.