Lamarck's Theory

Jean-Baptiste de Lamarck, in his 1809 book 'Philosophie Zoologique', was the first to formally propose a theory of evolution, resting on two principles. The theory of use and disuse holds that organs used frequently grow larger and stronger over an organism's lifetime, while organs not used degenerate — the long neck of the giraffe (stretched repeatedly to reach high foliage) illustrates 'use', while the absent limbs of snakes illustrate 'disuse'. The theory of inheritance of acquired characters then claims that such lifetime-acquired changes are passed on to offspring. This second principle was experimentally disproved by August Weismann, who bred mice for twenty successive generations, amputating each generation's tail before breeding — yet every single mouse born throughout the experiment still had a full tail. Weismann concluded that changes to the somatoplasm (body cells) are not heritable, while only changes to the germplasm (reproductive cells) can be passed on — a distinction Lamarck's theory had not made. Later followers known as the Neo-Lamarckists (Cope, Osborn, Packard, Spencer) tried to put Lamarck's ideas on firmer scientific footing, arguing that environmental conditions stimulate somatic cells to release 'secretio …