Charles Darwin (1809–1882) was a British naturalist who proposed one of the most influential theories in biology. After a five-year voyage on HMS Beagle (1831–1836), during which he observed diverse organisms across continents and islands, Darwin developed his theory of evolution by natural selection. He published his findings in 'On the Origin of Species by Means of Natural Selection' in 1859.
Darwin's theory rests on two central ideas:
Darwin proposed that all living organisms are related through common ancestry. Over vast periods of time, populations accumulate changes (modifications), giving rise to new species. This can be visualised as a branching tree of life, where each branch represents a lineage diverging from a common ancestor.
All species alive today descended from ancestral species that lived in the remote past, with modifications accumulating over generations.
Natural selection is the mechanism Darwin proposed to explain how evolution occurs. It is based on four key observations and inferences:
Species tend to produce far more offspring than the environment can support. For example, a single pair of elephants could theoretically produce millions of descendants in a few centuries if all survived.
Individuals within a population differ from one another in heritable characteristics (e.g., size, colour, disease resistance). These variations are the raw material upon which natural selection acts.
Because resources (food, space, mates) are limited and populations overproduce, there is competition among individuals. Darwin was influenced by Thomas Malthus's essay on population, which noted that human populations grow faster than food supplies.
Individuals with favourable inherited traits are more likely to:
This is called differential reproductive success. Over many generations, favourable traits become more common in the population.
| Step | Observation/Inference |
|---|---|
| Overproduction | More offspring produced than can survive |
| Variation | Individuals differ in heritable traits |
| Struggle for Existence | Competition for limited resources |
| Differential Survival | Individuals with favourable traits survive and reproduce more |
| Evolution | Favourable traits increase in frequency over generations |
While natural selection acts on individuals, it is the population that evolves over time. The frequency of favourable alleles increases in the population across generations.
Darwin's original theory had one major gap: he could not explain the source of variation or the mechanism of inheritance. This was later addressed by Neo-Darwinism (Modern Synthesis), which integrated Mendelian genetics with natural selection.