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4.3.1. Lamarck


Jean Baptiste Pierre Antoine de Monet, Knight of Lamarck, was the first naturalist to develop a coherent theory of evolution. For this reason, he had a great confrontation with the followers of fixist theories.
Lamarck studied invertebrates, present-day invertebrates, and fossils. In fact, Lamarck is considered the founder of invertebrate paleontology. When studying the fossils, he observed that some had an intermediate appearance between some older and others more modern, which led him to think that some came from the other.
He also observed that current species are more complex than extinct species, which is why he deduced that species become more complex over time.

The fundamental ideas of Lamarck's transformist theory are:

  • Importance of the environment. Changes that occur in the environment make organisms have to make an effort to adapt to the demands of their habitat. These environmental changes are the engine that drives changes in organisms. That is, living things change to adapt to their environment.
  • The use and disuse of organs. Changes in the environment make organisms have new needs. Organisms develop the organs and structures they need to adapt to new conditions. Some organs use them a lot and others little. Those most used will have greater development than those less used, so the organism will be modified. Even if an organ is not used, it can shrink and even disappear.
  • The function creates the organ. The use of an organ strengthens and improves it, evolves. If environmental changes create new needs in organisms, totally new organs may arise in response to these changes.
  • Inheritance of acquired characters. The new characters that have appeared in organisms, as a consequence of their adaptation to the new conditions of the environment, are transmitted to the offspring. In this way, these new characteristics are inherited by the descendants.

This is how Lamarck explained how, by adaptation to environmental conditions, the different species that have lived on our planet had appeared over the years.

Examples of Lamarckism

For Lamarck, kangaroos and ostriches have highly developed legs because they use them a lot. In contrast, both the wings of ostriches and the upper limbs of kangaroos, since they were not used, were reduced in size.

The horns of male deer are very large to use. As fights with other deer are frequent, they develop and become more resistant.

Origin of giraffes

An animal similar to an antelope lived in an increasingly dry environment, where grass and bushes were increasingly scarce, it had the need to feed on the leaves of the trees. The need to stretch his neck, more and more, led him to have a stretched neck.

Those who did not stretch their necks tended to disappear, with little or no offspring. Those with long necks, in addition to surviving, had offspring to whom they transmitted this characteristic.

Thus, after many generations, giraffes appeared.

The flaws of Lamarck's theory

Surely it will have caught your attention that the body is modified by the fact of using a certain organ a lot. The body does not change shape to better perform a function.

It is true that some organs change with use. For example, you can become more muscular if you exercise with your arms, but that does not mean that this characteristic passes to your offspring, since the DNA does not have any change.

Although this theory cannot be considered as true, it was very important for science, since it paved the way for other evolutionary theories.


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