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NDA Biology · Genetics and Evolution

The Theory of Evolution

Evolution is the gradual change in the heritable characteristics of a population over many generations; Darwin explained it through natural selection — the survival and reproduction of the best-adapted individuals.

All Genetics and Evolution notesNDA Biology strategy

Why this matters

The NDA tests this as a one-line recall fact — most often 'who wrote The Origin of Species?' (Charles Darwin). Learn Darwin and the core idea of natural selection, and keep Lamarck (the disproven alternative) straight from Darwin. EASY recall.

Concept 1 of 2

What evolution means

Intuition

Living things are not fixed — over very long stretches of time, species change, and new species arise from older ones. This slow change in inherited traits across generations is evolution. It acts on populations over generations, never on a single individual within its lifetime.

Definition

Evolution is the change in the heritable characteristics of a population over successive generations — 'descent with modification'.

  • It operates on populations, not individuals, and over many generations.
  • The raw material is variation — small inherited differences between individuals.
  • Evidence for evolution includes fossils (the record of past life), homologous organs (same basic structure, different function — e.g. a human arm, a whale flipper, a bat wing) and vestigial organs (reduced, functionless remnants — e.g. the appendix).

Worked example

A bat's wing, a whale's flipper and a human arm all share the same arrangement of bones. What does this similarity suggest, and what are such organs called?
  1. The same underlying bone plan, used for different functions, points to a shared ancestor.
  2. Organs with the same basic structure but different functions are called homologous organs.
Answer:It suggests a common ancestor (evidence for evolution); such organs are homologous organs.

Concept 2 of 2

Darwin and natural selection

Intuition

Charles Darwin's big idea was natural selection: individuals vary, more are born than can survive, and those whose traits best fit the environment survive and leave more offspring. Over generations, the helpful traits become common — the population has evolved.

Definition

Charles Darwin published 'On the Origin of Species by Means of Natural Selection' in 1859, drawing on observations from his voyage on HMS Beagle (including the Galápagos finches). Natural selection rests on four observations:

  • Variation — individuals in a population differ in their inherited traits.
  • Overproduction — more offspring are produced than can survive.
  • Struggle for existence — they compete for limited resources.
  • Survival of the fittest — those best adapted survive and reproduce, passing on their traits.

Contrast Lamarck, whose theory of 'inheritance of acquired characters' (e.g. a giraffe stretching its neck and passing the longer neck to offspring) is now disproven — acquired (non-genetic) changes are not inherited.

Worked example

In a population of beetles, dark beetles are better camouflaged than light ones and so are eaten less by birds. Over many generations, what happens to the colour of the population, and what is this process called?
  1. Dark beetles survive more often and leave more offspring than light beetles.
  2. The dark-colour trait is inherited, so its frequency rises each generation.
  3. Selection by the environment favouring the better-adapted variant is natural selection.
Answer:The population becomes darker over time; this is natural selection (survival of the fittest).

From the bank · past-year question

Example 2Genetics and EvolutionEASY
The book The Origin of Species by Means of Natural Selection was authored by

[Q131 · Sep · 2025]

Darwin wrote 'The Origin of Species' — not Linnaeus or Lamarck

The distractors offer Carolus Linnaeus (who founded binomial nomenclature and classification, not evolution) and others. The Origin of Species (1859) is Charles Darwin. Linnaeus = naming/classification; Darwin = evolution by natural selection.

Darwin vs Lamarck

Darwin = natural selection acting on inherited variation. Lamarck = inheritance of acquired characters (use and disuse), which is disproven. Don't swap them — acquired traits during an individual's life are not passed on.

Summary — formulas & gotchas at a glance

A revision cheat-sheet for the formulas and gotchas above. Click any concept name to jump back to its full explanation.

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