Origins of Life: Theories of Creation and Evolution
Theories on the Origins of Life
The concept of creation is fundamental to religions across history and cultures. Understanding how life originated on Earth has been a central question in spirituality and philosophy.
Spontaneous Generation
In ancient Greece, the belief that life could arise spontaneously under the right conditions was prevalent. Aristotle synthesized ideas about spontaneous generation, suggesting that certain beings could even be generated from plants. This theory persisted for over 2000 years until Francesco Redi (17th century) challenged it by demonstrating that fly larvae do not spontaneously generate from decaying meat.
Panspermia
Panspermia proposes that life arrived on Earth via bacterial spores from outer space, propelled by stellar radiation pressure.
Oparin’s Theory
In 1924, Oparin suggested that chemical compounds in the primitive atmosphere served as raw materials for synthesizing simple organic compounds. These compounds eventually led to the first living systems after a long period of prebiotic evolution.
Primitive Earth Conditions
The early Earth had a reducing atmosphere, lacking free O2, and composed of gases like CH4, NH3, H2O, CO2, and H2S.
Prebiotic Synthesis of Organic Molecules
Gases likely reacted impulsively, with rain washing chemical compounds into the oceans, creating a ‘primeval soup.’ These molecules reacted in water, leading to biological transformations. Simple building blocks interacted, forming giant molecules (biological polymers). Microstructures clustered within the soup, developing complex autoreproductive systems.
Fixism
Fixism proposes that species do not change but remain fundamentally unchanged since their creation.
Catastrophism
Catastrophism suggests that geological cataclysms destroy existing species, followed by the creation of new ones.
Lamarck’s Evolutionary Hypothesis
Lamarck’s hypothesis posits that species gradually transform into one another (the first function creates the organ, and acquired characteristics are inherited).
Darwin’s Theory
Darwin’s theory establishes a kinship between all living things. Current species result from the gradual adaptive divergence of species (high reproductive capacity, population variability, natural selection, species evolve).
Neo-Darwinism
The mechanism of hereditary trait transmission remained unclear until the 20th-century synthesis of Darwinian selection and Mendelian genetics (Neo-Darwinism). Key elements include: 1) the existence of genetic variability within populations, with a large number of different genotypes despite shared genes (mutations, genetic recombination); and 2) the role of natural selection as an evolutionary basis, eliminating less advantageous genotypes and altering gene proportions within populations (beneficial combinations appear).