From Spontaneous Generation to Evolutionary Evidence

Spontaneous Generation

Spontaneous generation proposes that life began from inanimate objects.

Oparin's Theory

Alexander Ivanovich Oparin developed this abiogenic theory.

1. Components of the atmosphere (methane, ammonia, hydrogen, and water vapor) reacted due to the energy of storms, solar radiation, and continuous volcanic eruptions, creating simple organic molecules.
2. The Earth cooled down, and intense rain produced primitive seas where organic molecules accumulated.
3. Organic molecules joined, creating bigger molecules; some of them were insulated from the water inside structures called coacervates.
4. Some of the coacervates developed molecules in their interior that were able to self-replicate; these were the first organisms and the origin of all cells.

Panspermia

The panspermia theory suggests that life arrived from outer space as microorganisms trapped inside meteorites. Molecular panspermia suggests that organic molecules arrived in this way.

Present Day

The primitive atmosphere was composed of carbon dioxide, nitrogen, water vapor, sulfur dioxide, and hydrochloric acid. One of the possible places in which living things could have first appeared is deep-sea hydrothermal vents. These places release inorganic matter that, along with water and carbon dioxide, formed the first organic molecules.

Self-Replication

Molecules able to self-replicate and were surrounded by a lipid layer were formed, creating the first prokaryotic cells.

Metabolism

Lipid bubbles that carry out chemical reactions were formed and later developed the ability to self-replicate.

Fixism

Fixism is the belief that living things do not change and, therefore, species always stay the same. Fossils showed different living things to those they could see, so they realized they must have come from other organisms that inhabited the planet sometime before them. George Cuvier was studying fossils and observed that most of them came from living things that had become extinct. He argued that there must have been several catastrophic events followed by periods of creation in the history of our planet. Evolutionary processes are slow, with no understanding of genetics, confronting religious doctrines.

Homologous Organs

Homologous organs have different functions but the same evolutionary origin. Divergent evolution refers to the changes from a common ancestor.

Analogous Organs

Analogous organs have the same function but different evolutionary origins. Convergent evolution refers to the changes that create similar structures in groups not related at all.

Vestigial Organs

Vestigial organs tend to disappear as they are no longer useful because of changes in habits.

Fossil Evidence

Fossils show evolutionary lineage. Fossils are evolutionary links. Organisms that have not changed, or just very little, are known as living fossils.

Embryological Evidence

When embryos of different species are similar, there is an evolutionary relationship between them.