Lamarck (1744-1829) originally believed that all living things on earth were here just as they were created. The evidence that changed his thinking came fossils from mollusks such as clams and snails. The 1700s were a time of great exploration of the earth. New species and fossils were being found at a tremendous rate. Often a new species was found in fossil form and was sometimes found later as a living specimen. Lamarck originally thought that those species known only as fossils had a living specimen somewhere on earth, but it had yet to be found. He accepted the view that the fossil forms changed to the species we have living today since he did not think that God would allow extinction to happen.
He thought that God had created the world perfectly and extinctions would make the world less than perfect.
Lamarck’s model for how species changed over time included two explanations that were both natural, not supernatural. Life had begun in a simple form and then changed as the result of both
1. “power of life” (He wasn’t really sure what this “power of life” was.)
and the environment.
Lamarck’s views on how the environment interacted with living things are spelled out in two ideas. Neither includes the importance of variation in a species since Lamarck thought that a species is made up of an ideal type. This means that all the individuals of a species share the same characteristics so that you can tell them from another species. For example, all giraffes share the same characteristics, which is why they are called giraffes.
The first law says that by using a body part more, an animal will strengthen this body part little by little. The organ will develop, get bigger, and become more powerful if it is used more. It will become less powerful if it is used less. If an organ is not used, it will weaken deteriorate, and finally disappear. This became known as the theory of use and disuse.
Lamarck often used the webbed feet of ducks and geese as an example for how using an organ strengthens it. He said that some birds need to go to the water to get food and spread their toes when they strike the water. The skin between the toes was stretched as a result of this and, with time, large membranes are formed.
Another example is that of shorebirds. They do not swim, but need to be near the water to find food. They start to sink in the mud and stretch their legs. Over time this makes them longer so they do not get their bodies wet.
There were many examples given by Lamarck for the idea of use and disuse. These included the lack of teeth in whales, the small eyes in moles, the absence of legs on snakes, and insects without wings.
The second law about the environment said that whatever organ or body part is changed by use is passed on to kids, but only if both the mother and father have the new feature. This was called the law of acquired traits. He proposed an experiment to illustrate this point. If the left eye of a male and a female baby were masked for life and then they had kids, and their kids had kids, at the end of many generations their left eyes would naturally disappear. After a great amount of time, the right eye would come little by little to shift its position to the middle of the head.
He gave the example of snails’ tentacles to show how new organs developed. He said that snails need to touch the things lying in front of them and they try to touch them with some part of their head. This sends “nervous fluid” and other liquids to the head. By doing this again and again, the nerves in the head will be come longer little by little. These are the tentacles on snails. If the snails with tentacles mate (or if they fertilize themselves), their kids will have tentacles.
There was little evidence to support Lamarck’s models. In supporting his claim that life changed from simple to complex, he could only point to how he had arranged the animal classes. He never explained how traits acquired in one generation could be passed on to the next. He never did design experiments to test his views, but only offered the many facts of observation and his models of use and disuse and acquired traits. He is important in the history of evolution since he had an idea of how things change over time (evolution) when most people thought that species did not change. He also helped to draw attention to extinction.