How did J. B. Lamarck explain the course of evolution in plants and animals?

According to Lamarck, changes in animals and plants under the influence of external conditions occur in different ways. So, plants perceive changes in conditions directly through metabolism with the environment. If the seed of a meadow plant growing in the lowlands is accidentally brought on a dry rocky hill, then, adapting to new conditions, the offspring of this seed will turn into a new variety. In a buttercup growing in water, underwater leaves are dissected into thin hairy lobes, and the leaves located on the surface of the water are wide and round, divided into simple lobes. In a related species of buttercup growing on moist soil, the leaves are not divided into thin lobes. Lamarck believed that when the seeds of the first type of buttercup are not in the water, but on moist soil, plants of the second type will grow from them. However, in reality this does not happen.
For animals, Lamarck has developed a more complex transformation mechanism, implemented in the following sequence:
• any significant change in external conditions causes changes in the needs of animals;
• this entails new animal actions and the emergence of new “habits”;
• as a result, animals begin to use organs more often, which they used little before; these organs develop and grow significantly, and if new organs are required, then they arise under the influence of needs “by the efforts of the inner feeling”.
Thus, Lamarck considered the direct influence of the environment to be the main factor in evolution. He attached great importance to “exercise” and “non-exercise” of organs, believing that exercise leads to their strengthening and the results of such training are passed on to offspring. Lamarck admitted that the desire, desire of the animal leads to an increased flow of blood and “other fluids” to the part of the body to which this desire is directed, causing its increased growth, which is then transmitted to the offspring.
As the first consistent and integral attempt to create an evolutionary doctrine, the Lamarck theory was progressive for its time. However, the evidence provided by Lamarck on the causes of species variability was not convincing. The main provisions of his theory were not deduced and proved on the basis of scientific facts, but were only a speculative construction. He did not explain where the “desire of organisms to progress” arises, which, according to Lamarck, is inherent in all living things and is the driving force of evolution, and why it should be considered a hereditary property of organisms to respond to external influences.

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