Human Evolution: From Australopithecus to Modern Humans

Key Concepts in Evolution

Species: A set of individuals that can reproduce with each other and create fertile offspring.

Speciation: A process driven by several factors:

• Natural selection: Natural selection favors some individuals over others.
• Genetic isolation: Members of two different populations within the same species can no longer reproduce with the other population.
• Gradual differentiation: After isolation, populations become increasingly different.
• Speciation: Over time, genetic changes produce such significant differences that it's no longer possible for two populations to produce fertile offspring.

Human Ancestors

• Australopithecus (6 million years ago): The first hominid, walked upright.
• Homo habilis (2.5 million years ago): Used rudimentary tools and instruments.
• Homo erectus (1.8 million years ago): Carved stones and controlled fire.
• Homo sapiens neanderthalensis (200,000 years ago): Made a great variety of specialized tools from stone.
• Homo sapiens sapiens (Cro-Magnon) (40,000 years ago): Same physical aspect as present-day humans. Created cave paintings.

Evolutionary Theories

Before the 19th Century

Previously, only non-evolutionary theories existed.

• Linnaeus: Stated that species had been created separately and independently by God.
• Cuvier: Explained the existence of fossils from species that had disappeared as a result of catastrophes that killed those organisms.

After the 19th Century

The first hypotheses of evolution were developed.

• Lamarckism: The theory of inheritance of acquired characteristics. Animals developed structures and organs that they needed to adapt to the environment. The new characteristics were transmitted to their descendants.
• Darwinism: Based on natural selection.

Evidence of Evolution

• Anatomical and morphological evidence: Includes homologous organs, analogous organs, and vestigial organs.
• Fossil Evidence: Shows that organisms in the past were different from organisms today. We can observe clear changes, including an increase in diversity and complexity.
• Embryonic evidence: Some embryos from different species are similar, demonstrating a clear evolutionary relationship between them.
• Biogeographical evidence: Groups of organisms that were isolated geographically evolved differently to form new species.
• Molecular evidence: All living beings are made up of the same type of molecules. By comparing the molecular sequences in different species, the evolutionary relationship can be established.

Neo-Darwinism

Combines Darwin's theory with modern genetics:

• Mendel's laws
• Mutations
• Genetic recombination
• Sexual reproduction produces variations in the offspring.