Jean-Baptiste Lamarck is often credited with a major breakthrough in modern evolutionary theory, because he was the first who was able to propose a mechanism through which the process of change of species proceeded. In addition, he expanded the definition of evolutionary change, saying that life began simply and became more and more complex. In 1809, he published his work Philosophy of Zoology. In it, he described part of the mechanism by which changes were gradually introduced into the species and transmitted from generation to generation. His theory is also sometimes called the theory of transformation or simply Lamarckism. Although today the main provisions of the theory of Lamarck are considered a big step forward in the theory of evolution, during his life he did not receive much recognition.
An example to explain the theory of Lamarck
A classic example used to explain its concept is the elongated neck of a giraffe. According to Lamarck’s theory, if an animal had to strain its neck for a long time in order to reach high branches, it eventually began to stretch. The main disadvantage of his theory was that he could not explain how this could happen, although he discussed the "natural tendency toward perfection."
Another example that Lamarck used was the toes of waterfowl. He suggested that for years straining toes, overcoming the resistance of water, these birds received elongated membranes to better swim. These two examples show how the use of an organ can change a characteristic feature of a species. By the same principle, Lamarck argued that the cessation of such work leads to atrophy of the trait. Penguin wings, for example, are smaller than other birds because they do not use them for flying.
Inheritance in the theory of Lamarck
The second main point of the evolutionary theory of Lamarck was devoted to the inheritance of acquired traits. The scientist believed that altered or acquired traits can be passed on to offspring. Giraffes with long necks will have offspring with long necks and not short ones. This type of inheritance is sometimes called the second law of Lamarckism. But he was refuted after the discovery of hereditary genetics.
The main point of Lamarck's theory of inheritance, which has stood the test of time, is the idea that evolutionary changes occur gradually and constantly. He studied ancient shells and noticed that the older they were, the easier they looked. From this, he came to the conclusion that the species began with simplicity and was subsequently complicated or improved.
Disadvantages of the Lamarck theory
What today is called Lamarck’s theory of evolution was not really his idea. The name of its real creator is lost in history. Lamarck described this theory in one of his books. And it was obvious that the original idea was not his own. The main provisions of the theory of J.-B. Lamarck became very popular, and as a result, ideas began to be associated with his name. Modern epigenetics is also not the result of the work of this scientist.
Lack of inherited traits
The main points of the theory of Jean-Baptiste Lamarck is a theory not of evolution, but of adaptation, which is only part of evolution. It is similar to natural selection, and not the evolutionary theory as a whole. Lamarck’s theory has ceased to be popular, since it was established that its first postulate, the principle of using and not using certain organs, can be applied to only a small number of organs, systems or devices. And for most hereditary traits, such a mechanism simply does not work.
Evidence of bankruptcy theory
The main provisions of the evolutionary theory of Jean-Baptiste Lamarck have not passed practical verification. An adult giraffe does not experience neck lengthening during his life, no matter how difficult it is for him to reach tall branches. Some organ systems actually degrade due to overuse. The constant use of joints does not make them stronger, but rather accelerates arthritic degradation. And some devices are used only once in the life of any animal, for example, spawning behavior of salmon. If the parent uses the adaptation only once and then dies, the question arises as to how any changes from reuse or abandonment can occur to go to all descendants.
Heredity and offspring
Finally, if this principle were common to all animals, one would expect that the offspring born at the end of the parent's life would have more developed acquired characteristics than the offspring that was born at the beginning of his life. Since the parent lived longer and had more time to acquire more characteristics, the transferred traits could be completely different. In addition, convincing evidence was found to be inconsistent with the main points of the evolutionary theory of J.-B. Lamarca, because many acquired traits are not inherited. But still, these traits continued to evolve and change over time. This suggests that the mechanism of inheritance, called Lamarck, cannot be the main cause of adaptive changes in the process of evolution. But on the other hand, this does not exclude the possibility that the mechanisms described by the scientist may be responsible for some evolutionary adaptations as insignificant. But so far there has not been a single observation of any trait developing as a result of the transfer of acquired characteristics.
What is epigenetics
Epigenetics is a mechanism by which a parent sometimes, in response to various environmental stimuli, can change gene expression or cell phenotype without changing DNA. This is basically a particular example of normal phenotypic plasticity, in which the body can change the pattern of gene expression of subsets of its own cells in response to environmental triggers. This can occur in gametes, therefore, it affects potential offspring. But this is by no means “inheritance of acquired characteristics”, as stated in the main provisions of the theory of Lamarck. No new features are purchased. Genes whose expression patterns have changed have already been there and are not changing. In other words, the potential for phenotypic plasticity was there, evolving, presumably, through Darwinian mechanisms several generations before.
The difference between unicellular and multicellular organisms
All that has changed is an expression of the phenotype. With the exception of additional mutations, which is a neo-Darwinian mechanism, there is no constant change in the inherited information transmitted to future generations in the long term. Thus, all that the offspring ultimately expresses is not a new or altered characteristic in general, but rather a trait that parents have always had the opportunity to express. But it is worth noting that all of the above applies primarily to multicellular life forms, which were the main types of organisms with which biologists were associated during Lamarck and Darwin. If we talk about the main provisions of the theory of Lamarck, it is worth mentioning that in the field of unicellular life, the difference between the new mutation and the “acquired characteristic” is rather blurred and more or less reduces to the question of semantics.