How did observations in nature lead to the formulation of the theory of evolution?

Answer 1

• No one knew how old the earth was, but geologists were beginning to make estimates that the earth was considerably older than explained by biblical creation. Geologists were learning more about strata, or layers formed by successive periods of the deposition of sediments. This suggested a time sequence, with younger strata overlying older strata.

• A concept called uniformitarianism, due largely to the influential geologist Charles Lyell, undertook to decipher earth history under the working hypothesis that present conditions and processes are the key to the past, by investigating ongoing, observable processes such as erosion and the deposition of sediments.

• Discoveries of fossils were accumulating during the 18th and 19th centuries. At first naturalists thought they were finding remains of unknown but still living species. As fossil finds continued, however, it became apparent that nothing like giant dinosaurs was known from anywhere on the planet. Furthermore, as early as 1800, Cuvier pointed out that the deeper the strata, the less similar fossils were to existing species.

• Similarities among groups of organisms were considered evidence of relatedness, which in turn suggested evolutionary change. Darwin's intellectual predecessors accepted the idea of evolutionary relationships among organisms.

Answer 2

Observations of variation among organisms in nature, such as differences in beak shape among finches on the Galapagos Islands, led scientists like Charles Darwin to propose the theory of evolution. Through these observations, Darwin hypothesized that variation within species and natural selection were mechanisms driving the adaptation of species to their environments over time.