Evolutionary Theories: From Lamarck and Darwin to Modern Biology

Evolutionary Theories and the Nature of Life

Early Concepts: Creationism and Fixism

Two early concepts attempted to explain the origin of species:

• Creationism: A conception rooted in religious beliefs, which posits that the universe and the various beings within it were created by a divine being or God.
• Fixism: The belief that living creatures of different species possess unchanging characteristics, meaning each individual is biologically identical to its parents.

Lamarck's Theory of Evolution

In his work, Philosophie Zoologique, Jean-Baptiste Lamarck laid out an evolutionary explanation for nature and life based on two core principles.

Core Principles of Lamarckism

1. The Function Creates the Organ: An organism's organs change based on use or disuse. For example, an organ might develop or atrophy. Lamarck called these new features acquired characteristics.
2. The Inheritance of Acquired Characteristics: These acquired traits, developed during an organism's lifetime, are then transmitted to its offspring.

Criticisms of Lamarck's Theory

• Only traits contained within an organism's genetic information can be transmitted to its offspring.
• The idea that organs are generated to meet a specific need implies a final causality (teleology) in biological phenomena, a concept that is widely rejected in modern science.

Key Aspects of Darwin's Theory

The Notion of Species and Aristotelian Thought

Darwin's theory contrasts with the Aristotelian view of inheritance, which held that everything has two types of properties: essential properties that define its type and accidental properties that can vary freely within that type.

The Principle of Natural Selection

The idea of natural selection arose from previously debated concepts. It is fundamentally based on the Malthusian principle that populations grow faster than their available food supply. This leads to a struggle for existence where not all individuals can survive and reproduce.

Fundamental Properties of Living Organisms

All living things share three universal biological properties:

1. The ability to selectively exchange materials with the environment, facilitated by membranes composed of lipids.
2. A series of chemical reactions (metabolism) that allow them to convert these materials into their own components.
3. The ability to replicate based on information stored in the DNA double helix, which constitutes the universal genetic material.