How life changed over time through natural selection
The Earth is very old and life arose from simple molecules. Oparin and Haldane suggested organic molecules formed in the early atmosphere, and Miller and Urey supported this by producing amino acids from gases and electric sparks. Evidence for evolution comes from fossils, which show gradual changes over time, from homologous organs, like the forelimbs of whales, bats and humans that share structure but differ in function, and from analogous organs, like the wings of birds and insects, which have similar functions but different origins. Embryology and DNA comparisons also show shared ancestry.
Darwin’s theory of natural selection states that organisms vary, more offspring are produced than can survive, and those with useful variations survive and reproduce more. The peppered moth in industrial England is a classic example. Mutations, gene flow, genetic drift and recombination change gene frequencies; the Hardy–Weinberg principle describes allele frequencies that stay constant without these forces. Adaptive radiation, such as Darwin’s finches, produces many species from one ancestor. Human evolution includes ancestors such as Homo habilis, Homo erectus and Homo neanderthalensis, leading to Homo sapiens.
Why it matters
Evolution explains how bacteria become resistant to antibiotics and insects resist pesticides, which shapes medical and farming practice. It helps scientists trace the origin of diseases and design vaccines for changing viruses. It also connects all of biology, explaining why living things share common cell structures and genetic code.
Key terms
- Natural selection
- The process by which organisms with favourable variations survive and reproduce more successfully.
- Homologous organs
- Organs with similar structure and origin but different functions in different organisms.
- Adaptive radiation
- The evolution of many species from a common ancestor into different habitats.
- Genetic drift
- A random change in allele frequency, especially in small populations.