The great variety of species is an issue that has attracted the interest of biologists and the scientific community in general. To provide an explanation of this complex phenomenon, two reference theories have been developed: fixism and evolutionism. A third conception, creationism, is inspired by religious beliefs according to which species have been created by God.
From fixism to evolutionism
In the IV century BC, the philosopher Aristotle argued that species maintained their physiological and anatomical characteristics in an unalterable way. In other words, living things do not change over time and their features are permanent or fixed. This view was maintained until the eighteenth century with scientists such as Cuvier or Linnaeus.
Later the French naturalist Jean-Baptiste Lamarck proposed an alternative theory, transformism. According to it, species incorporate progressive changes over time and species are somehow subject to an evolutionary mechanism.
The scientific approach of fixism connected with the creationist vision, since God is the one who has created the living species and these unalterably conserve their essence and characteristics. The logic of fixism was based on the idea of the immutability and perfection of God (God's creations must necessarily be perfect because the opposite would be to admit that a perfect being creates something imperfect and this question would be an obvious contradiction).
According to the vision of the fixists and creationists, fossils were interpreted as the remains of animals or plants that disappeared after the universal flood mentioned in the Bible.
Lamarckism gradually introduced the idea of evolution. Thus, according to Lamarck, the different species had changed to adapt to their corresponding natural habitats. In this sense, current life forms descended from other life forms of the past. These principles questioned the thesis of fixism, but served as the theoretical basis for a new paradigm, Charles Darwin's theory of evolution.
The theory of evolution marked the end of fixism as a scientific theory
For Darwin, species are subject to a process or law of natural selection. In this sense, animals transform or evolve because different mutations appear in the offspring that favor a better adaptation to the environment and these mutations are inherited by subsequent generations (for example, a rabbit that is born with a larger coat can better protect itself from the cold and this new trait is transmitted to its future descendants until it finally ends up being selected by the species itself as a whole).
Photo: Fotolia - acrogame
