Synthetic Theory of Evolution
1. What is a Species?
A group of living things that share an evolutionary history, have common anatomical and physiological characteristics, and can reproduce to produce fertile offspring.
2. Main Proponents of Evolutionary Theories
Fijistas Theories
Species are products of a creator and are therefore fixed and immutable; they do not evolve.
Major Proponents:
- Plato and Aristotle: Although disagreeing on certain aspects of the natural world, they agreed that species were created and fixed.
- Carl Von Linné: Developed the binomial system of classification and nomenclature for living beings.
- Georges Cuvier: Known for his knowledge of fossils and considered the father of paleontology. Cuvier recognized that vastly different organisms existed in ancient times. He proposed that Earth’s geological history involved catastrophes that wiped out existing flora and fauna, leading to the emergence of new species.
3. Lamarck’s Theory
Lamarck’s theory is a transformational evolutionary theory. He believed nature created the first organisms, which were constantly modified. His theory is based on two principles:
- The function creates the organ: Adaptations arise from interactions with the environment. For example, the giraffe’s long neck developed from stretching to reach high leaves.
- Acquired characteristics are inherited: Characteristics acquired during an individual’s life are passed to offspring.
4. Uniformitarianism and Gradualism
Uniformitarianism proposes that the geological agents that shaped the Earth’s crust in the past are the same ones acting today (wind, water, volcanic activity). Gradualism suggests that changes in the Earth’s crust occur slowly and continuously.
5. Darwin’s Theory: Main Findings and Conclusions
- First Observation: Populations tend to increase geometrically, with offspring far outnumbering parents.
- Second Observation: Despite overproduction, the number of individuals in a population remains relatively constant.
- First Conclusion: Competition for resources (struggle for existence) determines survival.
- Third Observation: Individuals within a species vary.
- Second Conclusion: Individuals with favorable variations (the fittest) survive and reproduce, leading to natural selection.
6. Mutations and Their Advocates
Mutations introduce new changes into genetic material and are hereditary. Advocates: Hugo de Vries, Morgan, Huxley, and Muller.
7. The Synthetic Theory of Evolution (Neo-Darwinism)
In the 1930s, Theodosius Dobzhansky, Ernst Mayr, and George Simpson formulated the synthetic theory of evolution, or Neo-Darwinism. This theory integrates Darwinian concepts with modern genetics and fossil discoveries.
Neo-Darwinism:
- Microevolution (classic): New species arise from the accumulation of small variations caused by random mutations and recombination, selected by natural selection over long periods.
- Macroevolution: Considers that simple variations and random selection cannot explain all evolutionary leaps, incorporating concepts like genetic drift and speciation jumps.
The population is the genetic unit of evolution, and mutation is the mechanism that generates variation.
Postulates of the Synthetic Theory:
- Mutations and genetic recombination are random and the source of genetic variability.
- Natural selection acts on variations, favoring individuals adapted to their environment.
- In large populations, evolutionary changes result from the accumulation of small changes over long periods (gradualism).
- The biological species concept is dynamic: a group of individuals sharing an evolutionary history, similar characteristics, and the ability to reproduce fertile offspring.
8. Homologous Structures
Structures with the same evolutionary origin but different forms due to adaptation to different functions.
9. Analogous Structures
Structures with different evolutionary origins but adapted to perform the same function.
10. Vestigial Structures
Structures that were functional in ancestors but are now reduced and non-functional.
Population Variation
1. Population
The genetic unit of evolution; evolutionary processes occur within populations, not individuals.
2. Population Genetics
The study of populations, their genetic composition, changes over time, transmission of hereditary characteristics, and causes of genetic changes.
3. Gene Pool
The totality of genotypes in a population; the population’s genetic heritage.
4. Genotype Frequencies
The frequency of each possible genotype in a Mendelian population. For example, the proportion of birds with curved beaks (PP) in a bird population is calculated by dividing the number of birds with curved beaks by the total number of birds.
5. Factors Affecting the Gene Pool
- Genetic recombination: Increases genetic variability during sexual reproduction.
- Mutations: Introduce new genotypes beyond the limits of genetic recombination.
- Gene flow (migration): Incorporation of new genes from other populations.
- Natural selection and adaptation: Individuals with advantageous phenotypes are more likely to reproduce.
- Speciation: Formation of new species from existing ones.
6. Gene Flow
Gene flow (migration) is the transfer of genes from one population to another.