The Foundations of Evolutionary Theory: Darwin to Modern Synthesis

Darwin's Theory of Evolution by Natural Selection

In 1831, during a trip aboard the naturalist ship Beagle, Charles Darwin collected observations that allowed him to propose his theory of evolution. On a visit to the Galápagos Islands, he observed different species of finches. Although all species were quite similar, they presented very distinct specializations. Darwin suggested the idea that species develop in different directions when isolated from each other, but he could not fully explain the underlying mechanism.

Darwin assumed that there was a struggle for survival among animals, where only the strongest, fastest, and best adapted were able to survive. Nature acted as the sorter, determining which organisms would survive or perish based on the environment at the time. Darwin published his ideas in 1858, embodying them in his famous theory of evolution. One year later, he published On the Origin of Species, in which he explained his theory:

• Species change slowly; some disappear, and others appear.
• A large variability exists between individuals of a species, which allows some organisms to be better adapted to the environment than others.
• Natural selection chooses individuals with the most advantageous characteristics.

Neo-Darwinism: The Modern Synthesis

For some years, a new model, **Mutationism**, emerged. It advocated that favorable mutations were what truly drove the appearance of evolution. However, Mutationism eventually fell into oblivion.

The most important progress in Neo-Darwinism arose toward the end of the 1930s, led by scientists like Theodosius Dobzhansky, resulting in what is called **Gradualism** or the **Synthetic Theory of Evolution** (Modern Synthesis). This approach seeks to reconcile Darwin's ideas with new discoveries in genetics:

• New characteristics originate through mutation and recombination of existing genes.
• New mutations and combinations accumulate or disappear due to the action of natural selection.

Punctuated Equilibrium (Gould, 1972)

More recently, other scientists proposed new explanations. Stephen Jay Gould, in 1972, proposed the **Saltatory Theory** (or Punctuated Equilibrium), which challenges the idea that all taxonomic groups appeared gradually. This theory considers that species evolve very rapidly in short periods of time. However, once evolved, they stagnate for very long periods, remaining unchanged until sudden explosions of change break the static *equilibrium*, producing an evolutionary leap.