Before the Modern Synthesis:
* Darwin's theory of evolution: Focused on natural selection, the mechanism driving evolution. Darwin understood that variations existed within populations, but he didn't have a good grasp of how those variations were inherited.
* Mendel's laws of inheritance: Discovered in the 1860s, these laws explained how traits are passed down from parents to offspring. However, they were initially not connected to Darwin's theory.
The Modern Synthesis (1930s-1950s):
* Reconciling Darwin and Mendel: Key figures like Theodosius Dobzhansky, Ronald Fisher, J.B.S. Haldane, and Sewall Wright bridged the gap between Darwin's ideas and Mendelian genetics.
* Population genetics: This field emerged, studying how genetic variation changes in populations over time. It provided the mathematical framework for understanding how natural selection works on genes.
* Evolutionary biology: The Modern Synthesis established that evolution is driven by changes in gene frequencies within populations. It provided a comprehensive explanation for how new species arise and how existing species change over time.
Key points:
* Genes are the units of inheritance: The Modern Synthesis emphasized that evolution is about changes in gene frequencies, not just changes in observable traits.
* Mutations as the source of variation: Mutations create new alleles (versions of genes), providing the raw material for natural selection.
* Natural selection acts on variation: Natural selection favors traits that increase an organism's chance of survival and reproduction, leading to changes in gene frequencies over generations.
* Evolution is a gradual process: Evolutionary change typically happens slowly and incrementally, through small changes in gene frequencies over many generations.
In summary: The Modern Synthesis brought together Darwin's ideas on natural selection with Mendel's laws of inheritance, creating a unified theory of evolution that is still the cornerstone of modern biology.
