Biological Evolution: Theories and Evidence

Biological Evolution: Species Change Over Time

Biological evolution is the process of change in species over time.

Theories of Evolution

• Evolutionism: Species change and generate others (Lamarckism, Darwinism, synthetic theory, punctuated equilibrium).
• Fixism: Belief that species remain invariant over time.
• Creationalism: Explains the origin of species as creations of God, maintained immutable in the Bible.

Carolus Linnaeus established the binomial classification of species.

Catastrophism: Explains the existence and disappearance of species; species become extinct due to natural disasters.

Lamarckism: Species Change Over Time

• Organisms show a tendency toward greater complexity.
• Repeated use of an organ leads to its development (function creates the organ); disuse leads to degeneration.
• Acquired characteristics are inherited (theorem of the inheritance of acquired characteristics).

Darwinism: Natural Selection Causes Species Change

• Among organisms, there is a struggle for survival.
• Within a population, there is variability among individuals.
• The environment selects organisms that are better adapted.

Mutations: Alterations that occur randomly in genes, found in genes affecting gametes.

• Mutations can be harmful, neutral, or favorable.

Sexual Reproduction: Creates variability; genes are recombined, making individuals unique.

Selection Pressure: Factors that negatively affect the survival of individuals.

Tests of Evolution

Comparative Anatomy

Study of the anatomical structures of organisms to establish possible kinship between them.

• Homologues: Have the same internal structure but different functions.
• Analogues: Have the same function in different organisms but different structures.
• Vestigial Structures: Organs whose function is lost over time.

Fossil Record (Paleontological)

Fossils: Remains of beings that lived in the past. The fossil record is incomplete.

Embryological and Cellular Comparison

Study of the development of embryos of different animals.

Biogeographic Evidence

Distribution of Species: Study of where species are located.

Neo-Darwinism

• Rejects Lamarckism.
• Evolution occurs in a gradual way.
• Populations evolve, not individuals.
• Natural Selection (SN) acts on genetic variability (VG).
• Genetic variability is due to mutation and recombination.
• Isolation between species is a factor.

Speciation

Speciation: The process leading to the formation of new species from existing ones.

• Reproductive Isolation: Occurs until reproduction between groups becomes impossible.
• Geographical Isolation: Species become separated and, over time, may no longer be able to reproduce.