Major Theories and Scientific Evidence of Evolution

Major Theories of Biological Evolution

Lamarckism: Inheritance of Acquired Characteristics

Lamarckism is a theory of evolution proposing that species are the result of a long process of gradual change, progressing from simple to complex forms. Its key principles include:

• Tendency toward Improvement: All organisms strive for improvement through an inherent vital impulse.
• Law of Use and Disuse of Organs: Environmental changes necessitate an increase or a diminution in the use of certain organs. These organs develop more or less depending on their use.
• Function Creates the Organ: Environmental changes give rise to new needs, which can develop an organ shaped in response to that function.
• Inheritance of Acquired Characteristics: Changes acquired by an individual during its lifetime (due to use or disuse of an organ) become fixed and, if they affect the germline, are transmitted to the offspring.

Darwinism: Evolution by Natural Selection

Darwinism is the theory developed by two Englishmen, Charles Darwin and Alfred Russel Wallace, who independently formulated the concept of natural selection to explain the origin of species. It is based on three main pillars:

• Variability: Individuals of the same species show differences between them; there is great variability within a population.
• Environmental Selection: The environment affects the survival of individuals. Since individuals are not identical, the probability of survival for each is different. Nature selects the organisms best adapted to the environment.
• Inheritance and Differential Reproduction: Characteristics are inherited from parents to offspring. Individuals with a greater probability of reaching adulthood are more likely to reproduce, thereby transmitting their favorable characteristics to the next generation.

Neo-Darwinism: The Synthetic Theory of Evolution

Neo-Darwinism is the unifying theory that attempts to explain evolution and all its mechanisms through the study of populations and genetics. It is also known as the Synthetic Theory of Evolution.

• Focus on Population: This theory studies a population directly, rather than focusing solely on an individual.
• Genetic Variability: It is based on the existence of genetic variability—the presence of a wide range of genotypes obtained randomly from a population's genetic background (e.g., through mutation and recombination).
• Natural Selection Acts on Phenotypes: Natural selection acts on phenotypes, causing more favorable traits to leave more offspring, thus increasing the frequency of the responsible genes within the population.

Scientific Evidence Supporting Evolution

Evidence Based on Morphology and Comparative Anatomy

Anatomical evidence suggests that species originated from a common ancestor but have varied over time, adapting to new conditions.

• Homologous Organs: These organs have a similar internal structure, inherited from a common ancestor, but they may perform different functions. This pattern leads to divergent evolution.
• Analogous Organs: These are organs that perform the same function but have very different internal structures. This pattern is the result of convergent evolution.
• Vestigial Organs: These are residual organs present in the body that no longer develop or perform their original capability.

Other Lines of Evidence

• Embryological and Cellular Evidence: Based on the comparative study of embryonic development in different animals.
• Biochemical Evidence: Based on the comparison of the sequence of macromolecules, such as nucleic acids (DNA/RNA) and proteins, across different species.