The Origin and Evolution of Life: From Bacteria to Humans
The Living Planet: From Bacteria to Humans
The Origin of Life
- A creature performs three vital functions (nutrition, relationships, and reproduction) and consists of one or more cells.
- The chemical elements that constitute living things are mainly C, H, O, and N.
- Other elements are present in very small quantities but are essential for smooth operation (iron, iodine, etc.).
What Are the Theories About the Origin of Life?
- Spontaneous generation: For centuries, there was a belief that life was created from inert matter (sludge worms, flies from meat, etc.).
- Various scientific experiments were carried out to discard this belief.
- Redi (1668)
- Pasteur (1860):
- Environmental microorganisms that break down organic matter colonize this area.
- He concluded that all living beings come from another creature.
How Did the First Living Being Originate?
- There are two scientific theories that try to explain the origin of life:
- The Panspermia: Life originated in space and traveled in the form of despores from one planetary system to another. But how could an organizational structure withstand cosmic rays and enter the atmosphere intact due to the high temperatures?
- Abiotic synthesis: Scientists Oparin and Haldane (1924) proposed a theory on the evolution of chemical gases in the primitive atmosphere to form primitive cells.
- 3.8 billion years ago, the primitive atmosphere was formed by compounds like methane, ammonia, hydrogen, and water vapor. These contain many elements that make up living matter (C, N, H, and O).
- When the temperature dropped, the water vapor condensed and formed clouds that resulted in rain, which gave rise to the primitive oceans.
- Solar radiation and electrical discharges provided sufficient energy for the components of the atmosphere to react, forming organic biomolecules (carbohydrates, fats, and simple amino acids, which reacted together to form more complex molecules).
- In 1953, Stanley Miller performed an experiment using gases present in the early atmosphere and managed to synthesize amino acids.
- Later, using similar experiments, the synthesis of nucleotides, components of DNA, was achieved (John OrĂ³, 1961).
- These organic compounds precipitated on the surface and were washed by rain to the ocean, where they formed the original stock.
- In-stock reactions took place, allowing the formation of more complex structures. Later, molecular associations produced hollow structures called coacervates that had nucleic acids inside; these were likely the precursors of the first cells.
- From the coacervates appeared the first heterotrophic cells, and therefore, organic matter began to become scarce.
- Later, autotrophic cells appeared, which began to produce new organic matter and oxygen.
- Subsequently, heterotrophic cells that use oxygen appeared.
- Finally, the ozone layer was formed, which allowed the colonization of the terrestrial environment by different species.
Biological Evolution
It is the transformation of species over time.
- Aristotle established the scale of nature in which organisms are organized as a hierarchy (from simple to more complex organisms). But he considered that the similarity between certain organisms was due to their proximity on the scale.
- Until the beginning of the 18th century, Fixism was accepted: all living things were created at the beginning of time and remained invariant. This theory was tied to creationism, which explains the origin of species as creations of God that remain unchanged over time.
- But there was a factor that was difficult to explain: fossils.
- Georges Cuvier (1769-1832) proposed that these fossils belonged to extinct organisms.
- To show how Fixism was compatible with the increasing number of fossils, he proposed the theory of successive creations or the great cataclysms: living things were different from the current ones, remained unchanged for a long time, and became extinct after a natural disaster. After several extinctions, new species emerged. This phenomenon would occur from time to time.
- Evolutionism opposed Fixism, especially from the 19th century onwards. Evolutionists claim that living things change over time from other existing ones, forming new and different species.
- Jean-Baptiste Lamarck (1744-1829): was the first to develop a theory of evolution.
- Law on the use and disuse of organs: The environment is changing, and organisms adapt to these changes. Changes in the environment originate in organisms a need for adaptation to new living conditions. This causes an increase or a decrease in the use of some organs, making them more or less developed, and creating a modified organism. Therefore, the function creates the organ.
- Inheritance of acquired characteristics: For these new features to be perpetuated and increased, they need to become hereditary.
This theory is of great historical interest, but it is false; acquired characteristics are not transmitted to offspring, and therefore, several species have not emerged from adaptation to different environments.
- Charles Darwin (1809-1877)
In 1831, he embarked on the Beagle, a ship that launched a scientific expedition around the world.
On this journey, he made many observations, and once in England, he published a book that created great controversy: The Origin of Species
Alfred Russel Wallace (1823-1913) also reached almost the same conclusions as Darwin: natural selection is the mechanism by which species change over time.