Darwinism and Neo-Darwinism: Evolution Explained

Darwinism

Charles Darwin (1809-1882) and Alfred Russel Wallace (1823-1913)

Basic Principles of Darwinism

1. Individuals within a population have anatomical, physiological, and behavioral differences.
2. Each species produces more offspring than can survive to reproductive age, leading to competition.
3. Competition for resources (struggle for existence) explains why many offspring die.
4. Natural selection favors individuals with advantageous variations.
5. Surviving individuals pass favorable variations to their offspring.

Survival of the Fittest

Individuals with favorable characteristics survive and become more common, potentially leading to new species over generations.

Example: Giraffes

1. Giraffes initially had varied neck and leg lengths.
2. Natural selection favored longer necks and legs, leading to increased reproduction.
3. Over time, long-necked and long-legged giraffes became more prevalent.

While Darwin explained species change, he couldn't explain the origin of variations. Modern genetics addresses this.

Neo-Darwinism

Discoveries Explaining Variation

• Mendel's laws of heredity
• Sexual reproduction and gene combination
• Genetic recombination during meiosis
• Mutations causing rapid gene changes

Example: Giraffes (Neo-Darwinian perspective)

1. Giraffe ancestors had short necks and legs.
2. Mutations and genetic recombination led to longer necks and legs in some individuals.
3. These advantageous traits increased reproduction.
4. The frequency of long-necked and long-legged giraffes increased.
5. Continuous mutations and natural selection further refined these traits.

Neo-Darwinism emphasizes natural selection acting on populations, not just individuals.