Evolutionary Theories: Lamarckism, Darwinism and Genetics
Lamarckism: The First Theory of Evolution
Lamarck published the first theory of evolution. Evolutionary theories are those that explain the diversity of species as a result of successive changes in previous species. Lamarck's theory is based on three main points:
- Existing species come from other earlier species through successive changes.
- These changes are produced by an intentional effort to improve certain qualities. These characters are called acquired characters.
- These acquired characters are passed on to their descendants.
Darwin's Theory of Evolution
Darwin's theory is defined by three fundamental points:
- Variability: Populations of living beings are not uniform; they show variability. In a stable environment, the number of individuals and their variability are maintained.
- Adaptation: When faced with unfavorable changes in the environment, some individuals within the total variability show characteristics more suitable to the new environment, becoming better adapted.
Natural Selection
The better-adapted individuals will reproduce and leave more offspring more easily. These offspring inherit the characters that determine better adaptation. If this selection is repeated in each generation, the entire population will eventually possess the character that allows for easy adaptation.
Neo-Darwinism and the Synthetic Theory
After the death of Charles Darwin, the work of Gregor Mendel was discovered, marking the beginning of the genetics boom. Genetic knowledge was essential to resolve the questions Darwin faced. Scientists developed the Neo-Darwinian or synthetic theory, which was based on Darwinian principles but solved the doubts that remained in his time.
Evolutionary Mechanisms
Mutation
A mutation is a permanent change in DNA. If the change affects a single gene, it gives rise to new alleles and new phenotypes. It is a primary source of variability and occurs randomly. If mutations affect the DNA of the gametes, they can be passed to offspring.
Natural Selection
The number of individuals in a population of a species remains constant until the environment promotes change and increases the number of the fittest. This process is natural selection.
Genetic Drift
Genetic drift refers to the change in the proportion of an allele from one generation to another. This may lead to the selection of a character without it necessarily providing an advantage and without variations in environmental conditions. This typically occurs only in populations with few individuals.
Gradualism vs. Punctualism
Gradualism
Gradualism states that a population of a species accumulates changes gradually as it adapts to the environment. This accumulation leads to the appearance of varieties and subspecies first, followed by speciation. The appearance of new species is a gradual process. The main criticism is the lack of fossils, but proponents argue that fossilization requires specific conditions that were only met by a few species.
Punctualism
Punctualism (or punctuated equilibrium) suggests that a population of a particular species living in an environment does not change for long periods. Speciation occurs in a small portion of that population that becomes isolated in a different environment. These changes happen abruptly over a few years. Punctualism theory explains the failure to find fossils showing gradual changes.