The transformation of beings, such as man, is explained by resorting to evolutionary theories , whose authors are Juan Bautista Lamarck and Charles Darwin. These theories try to explain the evolution of man.
Lamarck (1744 – 1829)
He is a French scientist , he proposed three ideas for the evolution of man:
- The environment modifies the structure of plants and animals , just as a tree blown by a constant wind in one direction, leans in that direction and an animal living at the North Pole acquires warm fur
- The frequent use of an organ strengthens it and favors its growth , similarly to the disuse of an organ weakens it and leads to its disappearance. For example the blacksmith has strong arms, the dancer has strong leg muscles.
- Acquired characteristics are passed on to offspring . We have the case of giraffes that had to grow their necks in order to reach the foliage of the highest parts of the trees, therefore their descendants inherit their characteristics.
Charles Darwin (1809 – 1882)
He was an English naturalist who went around the world studying plants and animals and then classifying them. As a result of that great trip he contracted a tropical disease that forced him to lead an invalid life. Nevertheless he managed to publish twenty scientific books. One of them was The Origin of Species published in 1859 where he proposed the Theory of Evolution .
The fundamental characteristics of the theory of evolution are two:natural selection and the variability of the species .
Natural selection
It is that only the strongest, fittest, most adapted individuals survive, the rest die or are eliminated because they are not necessary.
This idea arose from reading the English economist Thomas Malthus, who argued that the number of births is so great that, if all descendants survive, a thick crust of life would soon form on the earth's surface; an oyster produces millions of young and yet the sea does not become a compact mass of molluscs.
The variability of the Species
It is the determined number of similar but not equal individuals that make up a species. The more favorable variations individuals have, the more options they have to survive and produce a greater number of offspring.