Why is Jean Baptiste de Lamarck a key figure in the history of evolution?

Jean Baptiste Lamarck was a French scientist who developed a theory of evolution at the beginning of the 19th century. His theory involved two ideas. The first was the law of use and disuse, which stated that a characteristic which is used more and more by an organism becomes bigger and stronger, and one that is not used, eventually disappears. The second law was the law of inheritance of acquired characteristics. It stated that any feature of an organism that is improved through use, is passed to its offspring. However, Lamarck’s theory cannot account for all the observations made about life on Earth. For instance, his theory would predict that all organisms gradually become complex and simple organisms disappear. But we know that this is not the case, and that simple organisms still exist. So today, Lamarck’s theory is largely ignored.