Key Theories and Concepts in Evolutionary Biology
Foundational Theories of Species Change
Fixism: Species Stability Theory
Fixism is the theory that species were created following a predetermined pattern and, therefore, have always remained the same.
Key proponents include Georges Cuvier and Carl Linnaeus.
Evolutionism: Species Transformation
Evolutionism defends the idea that species have changed and transformed over time.
Key proponents include Jean-Baptiste Lamarck, Charles Darwin, and Alfred Wallace.
Key Figures and Contributions
- Georges Cuvier: Catastrophism.
- Carl Linnaeus: Taxonomy. Developed the modern system of species classification and binomial nomenclature.
- Jean-Baptiste Lamarck: Authored Philosophie zoologique, proposing the first theory of evolution and the transmutation of species.
- Charles Darwin: Authored On the Origin of Species. Proposed that all species of life have descended from a common ancestor.
- Alfred Wallace: Independently conceived the theory of evolution through natural selection.
Lamarckism: The First Evolutionary Theory
Lamarck proposed the first comprehensive theory of evolution, now known as Lamarckism. It was initially received with hostility by the scientific community and was largely ignored until the evolutionary theories of Darwin and Wallace were published half a century later, reviving the evolutionism debate.
Although Lamarck’s evolutionary explanations are now considered erroneous, his work had an enormous impact at the time, not only as the first theory to oppose fixism, but because Lamarck developed his theory following a meticulous scientific method.
Premises of Lamarck’s Theory
Lamarck’s theory was based on three main premises:
- The Law of Progression (tendency towards complexity).
- The Law of Use and Disuse.
- The Inheritance of Acquired Characteristics.
Functionalism vs. Structuralism
- Functionalism: An animal’s way of life (its function) determines its structure. Example: Flies have wings in order to fly.
- Structuralism: The structure determines an animal’s way of life. Example: Flies fly because they have wings.
Evidence and Core Evolutionary Concepts
Evidence Supporting Evolution
Key fields providing evidence for evolution include:
- Palaeontology
- Biogeography
- Embryology
- Comparative Anatomy
- Biochemistry
Core Definitions
- Adaptation
- A hereditary physical, morphological, or behavioral change that provides greater biological fitness in a specific environment.
- Speciation
- The process where the accumulation of adaptive differences leads to the formation of new species.
- Species
- A set of similar individuals that behave as one reproductive unit.
Modern Evolutionary Theories
Synthetic Theory (Neo-Darwinism)
According to this theory, evolution is the result of the slow and gradual accumulation (gradualism) of small genetic changes in populations caused by mutations. These changes are regulated by the action of natural selection, which determines the selective survival of the fittest phenotypes.
Following the evolutionary pattern of gradualism, an ancestor species progressively becomes another through intermediate forms, leading to species divergence.
Punctuated Equilibrium Theory (Saltationism)
This theory was proposed in 1972 by US paleontologists Stephen Jay Gould and Niles Eldredge to explain gaps and discontinuities in fossil records.
It states that evolution does not always occur at the same speed, but intermittently jumps. There are long periods in which species remain stable (stasis), followed by shorter periods where evolutionary changes occur very quickly.
Following the saltationist theory, an ancestor species diversifies into other different species without passing through intermediate forms.
Neutral Theory of Molecular Evolution
This theory posits that the main mechanism of evolution is not natural selection, but rather the random actions of genetic drift and gene flow (migration).
Primate Classification (Human Lineage)
The taxonomic classification for humans (Primates) follows this order:
Haplorhines → Simiiformes → Catarrhini → Hominoidea → Hominidae → Homininae