The name Lamarck is very well known in the teaching of biology, being associated with an early effort to explain evolution. Nevertheless, when evolution is taught in the classroom, the only Lamarckian ideas that stand out are related to the ‘inheritance of acquired characters’, invariably illustrated by the example of the lengthening of giraffes’ necks, as a way of contrasting Lamarckian ideas with Darwinian natural selection. Our aim here is to argue that there are other important ideas in Lamarck’s work that are directly related to the origin and transformation of species. These concepts, causal explanations of organic nature, can be taught to students who are learning about the sources and development of evolutionary thought and will moreover provide the student with properly justified reasons as to why Lamarck’s explanation is considered to be the first wide-ranging and well-argued explanation of biological evolution. The Lamarckian concepts that we consider important for teaching evolutionary thought are the following: (1) the species as an arbitrary concept, directly related to the Lamarckian concept of the continuous transformation of species, (2) the ancestor–descendant relationship, and organic diversification from a common plan of organisation to a branching series, (3) gradual change, related to changes in environmental conditions, and (4) the controversy concerning the origin of life (that is, having either a natural cause or a divine origin), life’s transformation, and the natural origin of human beings, including our moral capacity, subjects which were related to Lamarck’s other political and philosophical interests.