Evolutionary Biology: Theories, Evidence, and Speciation

Creationist Theories

Creationist theories posit that all species are the result of divine creation. According to Fixism, all species have remained unchanged over time. Fossils are often used to justify catastrophism, suggesting that species existed as a result of subsequent catastrophes.

Evolutionary Theories

Evolutionary theories suggest that species vary in their characteristics over time to adapt to the environment they occupy.

Lamarckism: Basic Principles

• Species adapt to changes in their environment through daily life.
• These efforts result in acquired characters.
• These characters are inherited by the next generation, which continues to strive toward perfection.

Essentials of Darwinism

Natural populations present variability; not all individuals are identical. Environmental pressure ensures that only the best-adapted individuals survive. These survivors reproduce and pass their characteristics to the next generation, which then undergoes further selection.

Neo-Darwinism or Synthetic Theory

The rediscovery of Mendel's work and progress in 20th-century biology completed Darwinism. The source of variability is attributed to:

• Mutations: Introducing new characters.
• Sexual reproduction: Transmitting characters to the next generation in all possible combinations.

Industrial Melanism

Industrial melanism is a change in the dominant color of populations due to environmental changes caused by industrial activity.

Species and Speciation

A species is a set of individuals capable of reproducing and generating fertile offspring. Speciation is the process that determines the appearance of new species, occurring either gradually or abruptly over varying periods.

Evidence for Evolution

Palaeontological Evidence

Fossil series show the gradual variation of features, such as the increased size and reduced foot of the horse. Intermediate forms are also crucial evidence.

Anatomical Evidence

Homologous organs have the same origin and structure but different functions (e.g., dolphin fin, human arm, bird wing). This is a consequence of adaptation. Vestigial organs are those that have lost their original function but are still present.

Embryological and Cellular Evidence

Similar embryonic stages indicate a common origin. For example, all vertebrate embryos possess tails and gill openings during development.

Biochemical Evidence

The closer two species are evolutionarily, the more similar their molecules. Proteins and DNA of chimpanzees are very similar to humans, reflecting a common ancestor from six million years ago.

Biogeographic Evidence

Species on different continents and islands differ due to independent development. For instance, African monkeys differ from American monkeys, and species like the Myotragus were endemic to specific islands.