Neo-Darwinism, also called the Modern Synthesis, is the refined and expanded theory of evolution developed primarily in the 1930s and 1940s. It integrates:
Key contributors include Theodosius Dobzhansky, Ernst Mayr, George Gaylord Simpson, and Ronald Fisher.
Darwin's original theory had two major gaps:
Neo-Darwinism fills both gaps:
The gene pool is the total collection of all alleles present in all individuals of a population at any given time.
Neo-Darwinian definition of evolution: A change in the allele frequencies of a population's gene pool over successive generations.
This shifts the focus of evolution from the individual to the population — the individual cannot evolve; only populations do.
According to the Modern Synthesis, the primary sources of genetic variation are:
| Source | Description |
|---|---|
| Mutation | Changes in DNA sequence (point mutations, chromosomal mutations). The ultimate source of new alleles. |
| Genetic Recombination | Crossing over during meiosis reshuffles existing alleles into new combinations. |
| Gene Flow | Movement of alleles between populations through migration, introducing new alleles. |
Mutations are random with respect to fitness — they are not directed toward what the organism needs.
Neo-Darwinism identifies four main mechanisms that change allele frequencies:
The Modern Synthesis is supported by molecular biology:
This molecular evidence directly supports the Neo-Darwinian framework and aligns with SLO B-11-B-03.
| Feature | Darwin's Theory | Neo-Darwinism |
|---|---|---|
| Mechanism of inheritance | Unknown | Mendelian genetics |
| Source of variation | Unknown | Mutation + recombination |
| Unit of evolution | Individual | Population (gene pool) |
| Definition of evolution | Change in traits | Change in allele frequencies |