Biological Anthropology: The Evolution of Human Species

Biological Anthropology: The Theory of Evolution

From Fixism to Evolution

During the 19th century, the only accepted theory to explain the origin of humans and other species was fixism, which claimed that all species were originally created fully formed and complete, remaining unchanged to the present day. In essence, species were considered immutable.

Fixism had two primary approaches:

• Creationist: A higher being created the different species from the beginning.
• Naturalist: Nature, through natural processes, produced the various species.

At present, it is an accepted scientific fact that all animal and plant species are the result of the evolution of ancestral species.

1. The Theory of Evolution: Lamarck

The first scientist to propose a comprehensive theory of evolution was the French naturalist Jean-Baptiste Lamarck, who established two primary hypotheses:

1. The function makes the organ: Use or disuse of organs leads to their development or atrophy.
2. Transmission of acquired characteristics: Changes acquired during an individual's life are passed on as inheritance to their descendants.

This evolutionary theory does not withstand modern empirical testing, as acquired characteristics are not transmitted through an individual's genetics or heredity.

2. The Theory of Darwin and Natural Selection

All existing plant and animal species descend from earlier species. To explain this process, Charles Darwin proposed the law of natural selection, based on the struggle for survival of the fittest.

• The struggle for life perpetuates advantageous variations.
• Only the fittest survive and reproduce.

Darwin recognized that acquired traits are not transmitted hereditarily. The laws of inheritance were later discovered by Gregor Mendel. When Darwin's ideas were combined with Mendel's discoveries, the theory of evolution entered a new phase.

3. The Synthetic Theory

The synthetic theory (or modern synthesis) unifies Darwinian natural selection with other contributions, such as Mendelian genetics. After much controversy, this theory gained acceptance in the 1930s, explaining the evolutionary process in genetic terms.

Specific Features of Human Nature

Human evolution is marked by significant anatomical differences:

• Bipedalism: An upright, straight-legged position.
• Liberation of upper limbs: Hands and opposable thumbs facilitate manipulative skills and hand-brain interaction.
• Spinal alignment: The straightened spine and upright position allow for a panoramic view.
• Morphological transformations: Changes in the brain and skull, including increased weight and volume, favored the development of intellectual abilities.

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