Evolutionary Theories: From Fixism to Neo-Darwinism

Fixism vs. Evolutionism

To understand our present and future, it is crucial to know our origins. One key concept in this understanding is evolution, the theory that the universe and life are products of development, change, and adaptation, leading to the diversity of species. This stands in contrast to Fixism.

Fixism is a conception of living beings encompassing various theories. In our culture, the most widespread is the one that follows the Genesis narrative of the Bible. Proposed by George Cuvier, this theory posits that all species are independent and remain unchanged over time.

Lamarckism

This theory, proposed by Lamarck, applies primarily to animals and represents the first comprehensive theory of biological evolution. Lamarck's theory is based on the following principles:

• Gradual Progression: The idea of progression extends to all disciplines, often leading to evolutionary theories that view evolution as a process driven by various agencies.
• Adaptation to the Environment: This is the mechanism that produces gradual changes.
• Use and Disuse: The exercise of organs leads to their perfection and development. The adage "function creates the organ" encapsulates this idea.
• Inheritance of Acquired Characteristics: This allows for adaptation to the environment.

However, Lamarckism faces two main challenges:

• Changes in the body are not typically transmitted to descendants, as this would require changes at the genetic level (e.g., tattoos, piercings).
• It does not adequately explain adaptations to the environment in which the subject is passive (e.g., the fur color of animals).

Darwinism

Charles Darwin and Alfred Russell Wallace presented a new theory of evolution. According to Darwin, organisms engage in a struggle for survival because there are more living beings than resources. This leads to a process of natural selection, where those with the best characteristics to adapt to the environment are more likely to survive.

Darwinian theory opposed Lamarckism but initially lacked a mechanism to explain how variations are inherited. This required an explanation of heredity, such as that developed by Gregor Mendel.

Mutationism

Genetic research promoted mutationism, which posited that evolutionary progress was due to mutations. Hugo de Vries distinguished two types of variations:

• Modifications: Caused by environmental changes, these are not inherited.
• Mutations: Alterations in the genes of living organisms, these are transmitted through inheritance.

According to this theory, mutations are produced by random causes.

Neo-Darwinism or Synthetic Theory

The rivalry between proponents of natural selection and mutation led to the development of the Synthetic Theory of Evolution. This theory harmonizes the Darwinian principle of natural selection with genetic mutation.

According to this theory, mutations explain the chance variations in organisms that are inherited, while natural selection directs the course of evolution by eliminating less advantageous variations and perpetuating the best-adapted individuals.