Lamarckism: The theory of acquired characteristics put forth by Jean-Baptiste P.A. Lamarck (1744-1829), a French botanist, zoologist and biological philosopher.
According to Lamarck, evolution occurs because organisms can inherit traits acquired by their ancestors. Giraffes can only survive by eating leaves high up on trees so they stretch their necks to reach the leaves and this stretching of the neck is passed on to later generations.
The basic tenet of Lamarckism has been rejected. Darwinism (the theory of the origin of species and the development of higher organisms from lower forms through natural selection, the survival of the fittest, and the evolution of humans from an ancestor common to himself and the apes) has prevailed, together with the principles of transmission genetics.