Theories of the Origin of Life and Evolution
Early Theories About the Origin of Life
Creation
Religious texts, from the Bible or the Koran to the Hindu Vedas, each in its own way describes the origin of the world and living beings. Most of them describe creations made by a creator, God, or spirit, who acts on the matter or creates humans from the earth or rock.
Spontaneous Generation
Aristotle was the great synthesizer of ideas about spontaneous generation. He believed that certain beings could not only be engendered from their parents but also by decomposing organic and inanimate matter.
Louis Pasteur demonstrated that spontaneous generation did not exist; living beings only come from other predecessor living beings.
Panspermia
Anaxagoras thought that life was universal. It was not until the 19th century when Hermann Richter began to develop the idea that Earth was fertilized by microorganisms in space.
The theory of panspermia postulates that life came to Earth in the form of bacterial spores from outer space, driven by the radiation pressure of stars.
Modern Theories of the Origin of Life
Chemical Evolution of Life
In 1994, Oparin proposed that chemical compounds that existed in the primitive atmosphere were used as raw material for the synthesis of simple organic compounds. This theory reconstructs the origins of life from the chemical compounds of carbon in water.
Ore Genesis
It is likely that biological polymers were synthesized and accumulated in a primeval soup distributed on clay surfaces. Clays acted as biocatalysts, attracting and concentrating simple molecules on their surface and facilitating their polymerization to form the first polymers of biological interest.
Hydrothermal Vents
For some scientists, life originated at the bottom of the oceans. The starting point of all chemical evolution would have been hydrothermal vents, replacing the primitive atmosphere, where precursor gases such as CH4, NH3, and CO2 were dissolved at temperatures higher than 200 degrees.
RNA World
It is believed that RNA was the first biomolecule with storage capacity and catalytic properties to appear. The original RNA formed in the primitive oceans, rich in amino acids and proteins.
Living Evolution: Ancient Theories of Species Origin
Fixism or Creationism
This theory proposes that species do not change but remain basically unchanged over time since their creation. (Karl von Linné)
Catastrophism
Under this theory, each geological cataclysm destroys the existing species, after which a creation of new species is subsequently produced. (George Cuvier)
Evolutionary Theories
Lamarck’s Evolutionary Hypothesis
Lamarck’s hypothesis of evolution is called transformism and states that species evolve gradually, transforming into others. This hypothesis is based on two points:
- Function creates the organ: Each species progressively develops organs that are most used to carry out certain functions.
- Acquired characters are inherited: The series of amendments and characters acquired by an individual throughout his life are inherited by his descendants.
Theory of Darwinian Evolution-Wallace
This theory creates a bond of kinship between all living beings and is based on the following principles:
- High reproductive capacity of living beings.
- Variability of populations: There is great variability among individuals in a population and even among the descendants of the same pair, who have certain heritable characteristics.
- Natural selection: Among individuals within a population, there is a struggle for survival, which eliminates the less fit individuals whose traits were unfavorable. The best-adapted survive, showing some advantageous features. These are the ones that reproduce.
- Species evolve: Individuals that survive and reproduce pass their advantageous characteristics on to new individuals.
Neo-Darwinism: Synthetic Theory of Evolution
It is a union between the Darwinian selection theory and Mendelian genetics. According to this theory, evolution is due to two factors: genetic variability in the population and natural selection. (T. Dobzhansky)
New Theories of Evolution
Neutralism
According to this theory, natural selection is not pure chance, but rather the factor that varies populations in which a particular mutated gene can be dispersed without any selective advantage.
Saltationism
This theory raises the lack of intermediate steps in the fossil record, arguing that evolution occurs in jumps.
Classic Evidence
- Morphological: Similarities and differences that the same organ has in another species.
- Paleontological: The study of fossils, which are remnants of mineralized bodies that have been included in sedimentary rocks.
- Embryological: The study of the early development of organisms, that is, embryonic development.
- Taxonomic: The classification of living organisms, grouping those that have similar characteristics.