Darwin and Lamarck both suggest the development of different species on the basis of evolution, with changes taking place over time. Some of the mechanisms suggested by Lamarck are also involved in the theory offered by Darwin, but there are also differences between the two.
Lamarck suggests that species change because of a "felt need," and such needs make organisms respond creatively. For Lamarck, evolution takes place in an upward fashion and does so because organisms want this to be the case. Gould says that Lamarckianism is a theory of directed variation, meaning that a felt need is actually a perception on the part of the organism so that the need is then fulfilled and the organism changes, at least for subsequent generations. The Lamarckian approach has often been mistaken for the Darwinian approach, and people ask how organisms can progress deliberately, as if they were able to choose what they were and as if evolution had a direction, a purpose, and a conscious control.
Darwin's approach is not so simple and involves a two-part process. Adaptation is the process by which organisms respond to a change in their environment. These organisms evolve a new form, function, or behavior. Both Lamarck and Darwin accept the role of adaptation and base their theories on its mechanisms, and for both theorists, the environment conveys information to the organism bringing about the adaptive response. For Lamarck, the organism perceives the environmental change and adapts. In the Darwinian version, the first step is random and is known as genetic variation. The process is random because it occurs with no preferred orientation in adaptive directions. Selection is the next step, and this works with unoriented variation and changes a population by giving members greater reproductive success for certain advantages.
The process of adaptation is a survival mechanism which helps make the organism better able to survive and repr...