Origin and Evolution of Life: From Early Theories to Natural Selection
The Origin of Life: Early Explanations
Early explanations for the origin of life are deeply rooted in the realm of gods, mythology, and the supernatural. The life and death of loved ones were often attributed to these forces, as were any natural phenomena.
Early Theories
Aristotle developed the idea of spontaneous generation, according to which life arises without divine mediation from the combination of the four elements: fire, air, water, and earth. He described the birth of fish, mice, and insects from this process. A new current of thought laid the foundations of the scientific method, the structural pillar of modern science, which sees no explanation other than a mechanical one, or any valid procedure to confirm or refute a hypothesis other than experimentation.
Spontaneous Generation
Francesco Redi performed several experiments in which the credibility of the theory of spontaneous generation began to be questioned. The cell theory by Schleiden and Schwann states that the cell is the functional unit of life, all living beings are formed by cells, and all cells come from another cell. The experiment that definitively refuted the theory of spontaneous generation was that of Louis Pasteur (using swan-neck flasks).
Oparin and Haldane: Chemical Hypothesis of the Origin of Life
Oparin hypothesized that due to the action of the dominant energy sources present, inorganic substances (ammonia, hydrogen, and methane) could end up generating organic molecules. These molecules must have concentrated in the oceans, forming what he called “nourishing soup.” They would then combine to form increasingly complex structures that would eventually isolate themselves from the environment, giving rise to the first organisms.
Panspermia Theory
This theory states that life evolved in outer space and then colonized our planet. According to this hypothesis, very simple life forms exist throughout the universe, moving and colonizing planets where suitable conditions for development are present.
Biological Evolution
Biological evolution is the process of successive changes that occur in living beings throughout the generations.
Fixist Theories
These theories argue that the world is static and unchanging.
- Deluge Theory: Fossils are remnants of animals that did not survive the biblical flood.
- Cataclysm Theory: Presents successive episodes of extinction followed by immediate creations.
Evolutionary Theories
These theories admit that there is a continuous process of transformation of species (life forms are not static; they evolve and change continuously, with some becoming extinct).
Lamarck: Theory of Acquired Characteristics
From the naturalist Lamarck, a revolutionary new concept was introduced into the science of adaptation: a mechanism that living beings had to resist changes in the environment in which they live. Lamarck presented a theory called the Law of Use and Disuse, according to which organisms, driven by the need to live, react to environmental change by creating or enhancing a given organ. In the same way, the abandonment of the use of an organ leads to its atrophy or disappearance. Lamarck’s theory did not convince the scientific community because experimental verification did not support the idea of adaptation to a changing world. However, it is considered the first evolutionary theory.
Darwin and Wallace: Theory of Evolution by Natural Selection
Darwin proposed that only individuals carrying a particular trait or character that gives them some adaptive advantage over others will survive and reproduce. Wallace wrote a similar theory. The key concepts of their theories are:
- Random Variation: Among individuals of a population, there are different characters or varieties.
- Natural Selection: This is the mechanism that chooses the characters that confer an adaptive advantage to individuals, allowing them to reproduce and transmit these traits to the next generation.
- Gradualism: Over time, individuals carrying the adaptive character will become the majority in the population.