Natural selection

Lore & Background

For Darwin, natural selection was a law or principle resulting from three processes: inheritance (transmission of heritable material and its development), variation (partly from an organism's own agency), and the struggle for existence (including competition and cooperation). Variation of traits exists within all populations; some traits facilitate survival and reproductive success, making them more likely to be passed on. If the environment favouring these traits remains fixed, they become more common. Changes in a specific niche lead to microevolution; changes in the broader environment lead to macroevolution. New species can arise if new traits are radically different from predecessors.

Reader's Guide

Natural selection is a cornerstone of modern biology. The concept was published by Darwin and Alfred Russel Wallace in a joint presentation of papers in 1858 and elaborated in Darwin's 1859 book On the Origin of Species. Darwin described natural selection as analogous to artificial selection. The concept originally developed without a valid theory of heredity; the union of traditional Darwinian evolution with classical genetics formed the modern synthesis of the mid-20th century. New evidence has prompted 21st-century evolutionary biologists to challenge the gene-centred view, producing extended evolutionary syntheses that bring organisms back to the heart of the theory. While genotypes can change by random genetic drift, natural selection remains the primary explanation for adaptive evolution.

Did You Know?

• Natural selection was contrasted by Darwin with artificial selection, which is intentional.
• The likelihood of traits being selected is determined by factors including adaptation to environments, sexual selection, and fecundity selection.
• Pre-Darwinian thinkers such as Empedocles and Lucretius expressed the idea that only creatures that manage to provide for themselves and reproduce successfully persist.
• Aristotle considered whether different forms might have appeared accidentally but rejected this possibility, arguing that natural things come about in a given way.