Key Evolutionary Theories: From Fixism to Modern Synthesis

Evolutionary Theories: From Fixism to Modern Synthesis

Fixism vs. Evolutionism

Evolutionism emerged in opposition to fixism. While fixism posits that all species are independent and remain unchanged since their creation, evolutionism argues that the universe and life are products of continuous development, where species diversity results from change and adaptation.

Key Evolutionary Theories

• Lamarckism: The first comprehensive theory proposing a gradual progression from simple to complex organisms. It suggests that adaptation occurs through the use and disuse of organs, famously summarized as "the function creates the organ." It also posits that acquired characteristics are inherited.
• Darwinism: Based on the struggle for survival due to limited resources, this theory introduces natural selection. The fittest individuals survive and pass their traits to descendants. While influential, it initially lacked a mechanism to explain biological inheritance.
• Mutation Theory: This theory asserts that evolutionary progress depends on mutations. It distinguishes between non-inherited environmental variations and genetic mutations, which occur randomly and are passed down through heredity.
• Modern Evolutionary Synthesis: A synthetic approach that harmonizes Darwinian natural selection with genetic mutation. It explains that mutations provide the variations, while natural selection directs evolution by favoring the most adapted organisms.