Scientific Theories on the Origin of Life and Evolution
Spontaneous Generation and the Origin of Life
The theory of spontaneous generation suggested that life could arise from inert materials such as mud or sweat. This was believed for centuries, and Aristotle defended this theory. Later, the Italian physician Francesco Redi proved that the idea of spontaneous generation was erroneous. Eventually, Louis Pasteur showed that the theory was totally false, establishing that all living beings come from other living beings.
Oparin’s Hypothesis and Chemical Evolution
The Russian scientist A. Oparin believed that the appearance of life was due to a chemical evolution. The primitive atmosphere contained a number of gases which, upon cooling, created a primitive broth, eventually forming coacervates.
Experimental Synthesis of Organic Matter
Miller conducted an experiment that confirmed Oparin's hypothesis. Furthermore, S. Fox considered that amino acids at elevated temperatures created a series of proteins called thermal proteinoids, which formed small spheres named microspheres.
Nucleic Acid Synthesis and Extraterrestrial Origins
The Catalan scientist Joan Oró believed that the first organic compounds could have formed partly on Earth and partly from meteorites.
Current Hypotheses on the Origin of Life
A protobiont is known as an aggregate of molecules produced from abiotic forms.
Updated Oparin Hypothesis
According to this theory, the components that formed the membranes appeared first, followed by proteins (coacervates), and finally genes.
Eigen’s RNA World Hypothesis
M. Eigen proposed that the first molecular RNA was constructed from nucleotides alone.
Cairns-Smith Clay Hypothesis
According to the Cairns-Smith hypothesis, crystals of mineral clay formed first, followed by membrane enzymes, and finally genes in the form of RNA.
The Emergence of the First Organisms
The first prokaryotic cell originated through protobiological evolution quite rapidly, between approximately 200 and 500 million years ago.
Hypotheses on the First Eukaryotic Cell
Autogenous Hypothesis (Taylor and Dodson)
This suggests a prokaryotic cell compartmentalized its membranes to create some of the organelles of the eukaryotic cell.
Serial Endosymbiosis (Lynn Margulis)
According to the theory by Lynn Margulis, the eukaryotic cell comes from an ancestral cell that engulfed diverse anaerobic prokaryotic cells, creating a symbiosis.
Multicellularity and Metabolic Evolution
The first multicellular organisms are deemed to have formed from eukaryotic organisms that created colonies. These cells became specialized, providing form to tissues and forming all multicellular agencies.
Regarding the evolution of metabolism, it is inferred that the first organisms were prokaryotic heterotrophic fermenters. The ability to perform photosynthesis appeared later, with evidence found in stromatolites.