The Origin and Evolution of Life

Spontaneous Generation

The idea that life can appear from inanimate objects is known as spontaneous generation.

• In Ancient Egypt, people believed that the Sun's heat created life.
• During the Middle Ages, people created recipes to generate living things from materials.
• In the 17th century, scientists proved that spontaneous generation was not possible.
  • In 1668, Redi demonstrated that larvae found in rotten meat came from fly eggs.
  • In the 19th century, Pasteur demonstrated that microorganisms did not come from spontaneous generation, and this theory was finally rejected.

Origin of Life

Chemical Evolution

Chemical evolution is the process that formed the molecules that make up living things and their organization into membranes.

1. The first biomolecules to appear were simple molecules. These first biomolecules accumulated in the seas of the planet, forming a primeval soup.
2. These simple biomolecules then became more complex through chemical reactions.
3. Protocells, the precursors to living cells, formed.

Biological Evolution

Biological evolution includes the processes that caused the diversification of life on Earth.

1. Primitive cells, the first forms of life, emerged.
2. Different types of prokaryotic cells developed from these primitive cells.
3. The appearance of the first eukaryotic cells is explained by the endosymbiosis theory, which proposes that one cell engulfed another, and they began to live symbiotically.
4. From these early cells, all living organisms were generated.

Theories of Evolution

Lamarckism

The theory of inheritance of acquired characteristics, proposed by Jean-Baptiste Lamarck, says that animals developed organs and structures they needed to adapt to the environment, driven by an "adaptive force." These new characteristics were then transmitted to their descendants, leading to the modification of species. This theory is not supported by modern genetics.

Darwinism

Darwin's theory of evolution by natural selection is based on the following principles:

1. All individuals in a population have physiological, behavioral, and anatomical differences.
2. The number of individuals in any species is almost always the same.
3. There is competition to survive for space and food.
4. Individuals with traits that make them better suited to their environment (the "fittest") are more likely to survive and reproduce.
5. Each generation inherits more favorable variations, leading to gradual change over time. This process is known as natural selection.

Evidence of Evolution

• Anatomical Evidence: The existence of homologous organs (similar structures in different species), analogous organs (structures with similar functions but different origins), and vestigial organs (structures that have lost their original function) provides evidence for common ancestry and evolutionary change.
• Fossil Evidence: Fossils reveal that organisms in the past were different from those present today. They also show how species have evolved over time, such as the well-documented evolution of the horse.
• Embryonic Evidence: Similarities in the embryos of different species suggest a shared evolutionary history.
• Biogeographical Evidence: The distribution of species across the globe provides clues about their evolutionary relationships and how continents have moved over time.
• Molecular Evidence: Studying the molecules found in living things, such as DNA and proteins, reveals molecular similarities that support the theory of evolution. Closely related species share more similarities in their molecular makeup.