Modern synthesis (20th century)

The Modern Synthesis, also known as the evolutionary synthesis, refers to the unification of Charles Darwin's theory of evolution by natural selection with Gregor Mendel's theory of genetics. Developed primarily between the 1930s and 1940s, it provided a comprehensive and widely accepted explanation of how evolution works. Prior to the Modern Synthesis, there was significant debate and skepticism about the mechanisms of evolution, particularly regarding the role of natural selection and the nature of inheritance.

Key contributions and concepts integrated within the Modern Synthesis include:

• Mendelian Genetics: Genes are the units of inheritance, and variations in genes (alleles) lead to different traits. Genes are passed down through generations.

• Mutation: Random mutations in genes provide the raw material for evolutionary change. These mutations can be beneficial, neutral, or harmful.

• Population Genetics: The study of the distribution and changes in allele frequencies within populations. This provided a mathematical framework for understanding how natural selection acts on genetic variation.

• Natural Selection: The process by which individuals with advantageous traits (determined by their genes) are more likely to survive and reproduce, thereby passing on those traits to the next generation. Over time, this leads to changes in the genetic makeup of the population.

• Speciation: The process by which new species arise. The Modern Synthesis explained speciation as a gradual process of genetic divergence between populations, often driven by geographic isolation and natural selection, eventually leading to reproductive isolation.

• Gradualism: Evolutionary change occurs gradually over long periods of time, through the accumulation of small genetic changes.

Key figures who contributed to the development of the Modern Synthesis include Ronald Fisher, J.B.S. Haldane, Sewall Wright (population genetics); Theodosius Dobzhansky (genetics and natural selection in natural populations); Ernst Mayr (speciation and systematics); George Gaylord Simpson (paleontology and the fossil record); and G. Ledyard Stebbins (botany).

The Modern Synthesis addressed many of the shortcomings and unanswered questions of early Darwinian theory and became the dominant paradigm in evolutionary biology for much of the 20th century. While the core principles of the Modern Synthesis remain fundamental, contemporary evolutionary biology has expanded upon it to incorporate new findings from fields such as molecular biology, genomics, epigenetics, and developmental biology, leading to what is sometimes referred to as the "Extended Evolutionary Synthesis."