Charles Darwin used Thomas Malthus’s ideas about population and limited resources as the key “trigger” for his own explanation of evolution by natural selection. Darwin took Malthus’s social theory of a struggle for survival among humans and applied it to all plants and animals to explain how species change over time.

Core idea in one sentence

Malthus argued that populations grow faster than their food supply, creating a constant struggle for existence, and Darwin realized that in this struggle, individuals with helpful variations would survive and reproduce more, causing gradual evolutionary change.

What Malthus said

  • Malthus, in his Essay on the Principle of Population (1798), claimed that:
    • Populations tend to grow faster than the resources that support them.
    • This imbalance inevitably leads to competition, famine, disease, and a struggle for existence.
  • He was focused on human society, but the logic is general: when numbers increase and resources do not, not everyone can survive or reproduce.

Darwin before reading Malthus

  • Darwin already knew:
    • Species show lots of variation (for example, different beak shapes in birds).
    • More offspring are produced than usually survive (many eggs or seeds never become adults).
    • Farmers and breeders use artificial selection to produce new varieties by choosing which animals or plants to breed.
  • What Darwin lacked was a clear, automatic mechanism in nature that could act like a breeder to “select” some variations and eliminate others.

The “Malthusian moment”

  • When Darwin read Malthus in 1838, he suddenly saw how the struggle for existence could act as that natural mechanism.
  • He realized that:
    • In any population, individuals differ slightly in traits (size, speed, color, resistance to disease, etc.).
    • Because resources are limited and there is constant competition, not all individuals will survive and reproduce.
    • Those with advantageous traits are slightly more likely to survive, find mates, and have offspring.
    • Those offspring inherit the advantageous traits, so those traits become more common over generations.

How Darwin built on Malthus

Here is the step‑by‑step way Darwin extended Malthus’s idea:

  1. From humans to all organisms
    • Malthus wrote about human populations and economics.
    • Darwin generalized this to every species of plant and animal, seeing the whole natural world as engaged in a continuous struggle for existence.
  2. From struggle to selection
    • Malthus emphasized that many individuals must fail to survive or reproduce.
    • Darwin asked: if not all survive, which survive?
    • The answer: those with traits that fit their environment better. This is what Darwin named natural selection.
  3. From selection to evolution
    • Darwin then connected this selective survival to gradual change in species over long periods.
    • If favorable variations are preserved and unfavorable ones are destroyed, generation after generation, populations will slowly diverge, eventually forming new species.
  4. From social theory to biological law
    • Malthus’s idea was a pessimistic commentary on human society.
    • Darwin transformed it into a general biological principle explaining adaptation and the diversity of life.

Putting it together (short recap)

  • Malthus: populations grow faster than resources → inevitable struggle for existence.
  • Darwin: in that struggle, individuals with beneficial variations are more likely to survive and reproduce.
  • Over time, this natural selection of favorable traits leads to evolution and the formation of new species.

If you like, a next step could be a very short exam‑style answer you can use directly in homework or tests.