Looks like you are using an old version of Internet Explorer - Please update your browser
Darwin called natural selection “the preservation of favored races,” and he recognized that selection alone could not explain origin. When it came to the actual origin of new traits, Darwin wrote that it was “from use and disuse, from the direct and indirect actions of the environment” that new traits arose. About 40 years before Darwin, a famous French evolutionist, Jean Lamarck, argued for this kind of evolution based on the inheritance of traits acquired by use and disuse. Most books on the subject hint that we should laugh at Lamarck—but Darwin believed exactly the same thing.
Consider the supposed origin of the giraffe. According to both Darwin and Lamarck, the story begins back on the African prairies a long time ago. Because of prolonged drought, the prairie dried up. But there were green leaves up in the trees, and some of the animals started stretching their necks to reach them. As a result, their necks got a little longer (Fig. 15). Now that could be partly true. If you really work at it hard enough and long enough, you could add a little bit to your height. People used to do that to get into the army or some special service where you have to be a certain height. The problem, however, is that the offspring of “stretched” parents start off just as small as all the others. The long neck could not be passed on to the next generation.
Like others of his time, Darwin didn’t know about the mechanism of heredity. He thought that at reproduction each organ produced “pangenes” that would collect in the blood and flow to the reproductive organs. So, a bigger neck made more neck pangenes. Some people still believe this sort of concept. You’ve probably run into people who say, for instance, that people will eventually have bigger heads because we think a lot, and no toes because we wear shoes all the time. Darwin even used pangenes to “explain” why (in his opinion) wives grew to resemble their husbands as both got older.
Science has since disproved these “flimsy facts” of early evolutionary thought, but back in Darwin’s time, pangenes captured people’s imagination probably even more than natural selection did. To some, Darwin’s original theory of evolution suggested continual progress. How do you make something happen? By use and disuse. If you want to get smarter, use your brain, and both you and your children will be smarter. If you want to be strong, use your muscles, and not only will you get stronger, but so will your children.
Well, almost unfortunately, that’s not the modern theory of evolution. The use-disuse theory didn’t work and had to be discarded. A man named Weismann, for example, cut off the tails of mice for twenty-some generations, only to find that baby mice were still born with tails. Traits acquired by use and disuse just don’t affect heredity.