Darwinism and Natural Selection: Theory of Evolution
Darwinism is the theory of evolution by natural selection, proposed by Charles Darwin in 1859 in his book On the Origin of Species, and independently suggested by Alfred Russel Wallace. It explains how species change over generations and how new species arise, without needing any inheritance of acquired habits.
This theory matters because it is the foundation of all modern biology. Medicine, agriculture and conservation all rely on it, from breeding crops to fighting antibiotic resistance, which is natural selection happening in hospitals in real time.
Key Concepts
- Variation: individuals of a species differ slightly in heritable traits.
- Overproduction and struggle for existence: organisms produce more offspring than can survive, so they compete for food, space and safety.
- Natural selection (survival of the fittest): individuals whose variations suit the environment survive and reproduce more, passing those traits on. Fittest means best fitted and most reproductive, not simply strongest.
- Speciation: over long periods, accumulated differences can split one species into two that can no longer interbreed.
How It Works
- Within a population there is heritable variation, originally unexplained by Darwin and later explained by mutation and recombination.
- More offspring are born than the environment can support, causing a struggle for existence.
- Individuals with favourable variations survive better and leave more offspring; unfavourable variations are eliminated.
- Useful traits therefore become more common generation by generation, adapting the population to its environment.
- Isolated populations adapting differently can diverge into new species.
Darwins evidence included finches on the Galapagos Islands, whose beaks matched different foods, and artificial selection in pigeons and dogs, where human choice plays the role that nature plays in the wild. His main gap was not knowing how inheritance works, which Mendels genetics later supplied.
Worked Example
Take the classic case of peppered moths in industrial England. Before factories, suppose a woodland population of 1,000 moths had 990 light-coloured and 10 dark moths, because dark ones were easily seen and eaten on clean, light bark. Frequencies: light 99 percent, dark 1 percent. When soot darkened the trees, birds ate the now-visible light moths more. If dark moths survived twice as well and reproduced accordingly for several generations, the dark form could rise to, say, 900 out of 1,000, or 90 percent, as actually observed near industrial cities in the 1900s. Step by step: environment changed, heritable colour variation existed, selection favoured dark moths, and their frequency multiplied from 1 percent to about 90 percent, a 90-fold increase. When air later cleaned, the trend reversed. No moth willed itself darker; selection changed the population.
Common Misconceptions
- Survival of the fittest does not mean the strongest or fastest; a small, well-camouflaged, highly reproductive organism can be fittest.
- Individuals do not evolve during their lifetime in Darwins theory; populations evolve over generations as trait frequencies change.
- Humans did not evolve from present-day chimpanzees; both share a common ancestor that lived millions of years ago.
Real-World Applications
Farmers and doctors fight natural selection daily: pests evolve pesticide resistance and bacteria evolve antibiotic resistance, so doses and drugs must be rotated and used fully. Breeders use the same principles through artificial selection to produce high-yield wheat, dairy cattle and disease-resistant crops.
Darwinism explains adaptation by variation, struggle and natural selection acting over generations. Completed later by genetics, it remains the unifying theory of the living world.