Understanding Evolutionary Theory: Fixism vs. Darwinism

Evolutionary Thought: From Origin to Modern Synthesis

The Human Desire to Know Origins

The desire to know where we come from and how we arrived at our current state is essential to understanding the origin of our species, according to established theories.

Fixism Contrasted with Evolution

Fixism, proposed by George Cuvier, posits that species are independent entities and have remained unchanged since their creation.

Conversely, Evolutionism suggests that the universe and life result from development. Species diversity arises from continuous changes and adjustments. While the foundations of evolutionism began in the eighteenth century, the theory solidified during the nineteenth century.

Lamarck's Theory of Evolution

Lamarck's theory rests on several key foundations:

• Organisms progress from simple to more complex forms.
• Simple organisms need to adapt to environmental changes.
• This adaptation results in the use or disuse of certain organs.
• Organs used frequently develop and perfect themselves; those abandoned atrophy.

This leads to the principle: "The function shapes the organ." Inherited properties resulting from these adaptations are passed to offspring.

Darwin's Theory of Natural Selection

Darwin's theory emerged from observing the struggle for survival among living beings, where resources are often scarcer than the potential population size.

The consequence is natural selection. The fittest individuals—those best adapted to the environment—are the ones that survive and reproduce. Those unable to adapt perish.

Characteristics that aid survival are passed on to subsequent generations. While Darwin's ideas were revolutionary, he could not fully detail the mechanism of inheritance (which Lamarck's theory lacked explanation for).

Neodarwinism: The Synthetic Theory

Neodarwinism, or the synthetic theory, arose from combining the concepts of natural selection with the understanding of heredity and variation.

The basic thesis is that evolution is driven by natural selection acting upon inherited mutations, which are inevitable results of changes within the organism's organization.

Evolutionary Reality

Mutations that are not beneficial lead to species disappearing over the long term. Evolution is an undeniable reality in biology, though the precise mechanisms continue to be a subject of extensive scientific discussion.