French naturalist Lamarck was the first to propose a synthetic theory of evolution.
His theory was published in 1809 in the book Zoological Philosophy. He said that simpler life forms arise from inanimate matter by spontaneous generation and progress to a stage of greater complexity and perfection.
In his theory, Lamarck argued that the progression of organisms was driven by the environment: if the environment changes, organisms try to adapt to it.
In this adaptation process, one or more organs are used more than others. The use or disuse of the different organs would alter body characteristics, and these characteristics would be passed on to future generations. Thus, over time the organisms would change, giving rise to new species.
According to Lamarck, therefore, the evolutionary principle would be based on two fundamental laws:
Law of use or disuseIn the process of adaptation to the environment, the use of certain parts of the body of the organism causes them to develop, and disuse causes them to atrophy;
A classic example of the law of use and disuse is the growth of the giraffe's neck. According to Lamarck: Due to the giraffe's effort to eat the leaves of the taller trees, the neck of the giraffe eventually grew.
Law of transmission of acquired characters: Changes in the body of the organism caused by the use or disuse are transmitted to the offspring.
There are several examples of the lamarist approach to evolution. One refers to waterfowl, which would have become waders due to the effort they made to stretch their legs and thus avoid getting their legs wet while moving around in the water. With each generation this effort would produce birds with higher legs, which transmitted this trait to the next generation. After several generations, the current waders would have originated.
At the time, Lamarck's ideas were rejected, not because they spoke of inheritance of acquired characteristics, but because they spoke of evolution. Nothing was known about genetic inheritance and species were believed to be unchanging. Only much later could scientists challenge the inheritance of acquired characters. A person who practices physical activity will have more developed muscles, but this condition is not transmitted to their descendants.
Although he was mistaken about his interpretations, Lamarck deserves to be respected, as he was the first scientist to question fixism and defend ideas about evolution. He also introduced the concept of the adaptation of organisms to the environment, very important for understanding evolution.