Evolution as change in heritable characteristics

Ecosystems (Unity and diversity) · Evolution and speciation · note 1 of 4

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Evolution as change in heritable characteristicsSpec A4.1.1

In short

Evolution is change in the heritable characteristics of a population. The change is genetic: allele frequencies in the population shift over generations. Characteristics acquired during an organism's life, such as larger muscles or a scar, are not coded in its genes and are not inherited, so they are not evolution. This distinguishes Darwinian evolution from Lamarckism.

Evolution is change in the heritable characteristics of a population. Heritable means coded in the genes and passed from parents to offspring. Evolution therefore happens to populations over generations, not to individuals during their lives.

At the level of genes, evolution is a change in the frequency of alleles in the gene pool of a population. A new allele may arise by mutation, then become more or less common in later generations.

A characteristic an organism acquires during its life is not evolution. Larger muscles from exercise, a scar, or a plant growing tall in fertile soil do not change the DNA in gametes, so they are not inherited.

Darwinian evolution and Lamarckism compared
	Lamarckism	Darwinian evolution by natural selection
Where variation comes from	Organisms change during their lifetime through use or disuse of structures	Heritable variation already exists between individuals, from mutation and sexual reproduction
What is inherited	Acquired characteristics	Only genetic (heritable) characteristics
What changes	Individuals	The population: allele frequencies shift over generations
Status	Not supported: acquired changes do not alter the genes passed on in gametes	Supported by a wide range of independent evidence

Common mistake:

Do not write that an individual organism evolves or adapts in order to survive. Individuals survive or die; the population evolves.

Exam tip:

Nature of science: evolution by natural selection is called a theory because no theory can be formally proved true, not because it is weak. It predicts and explains a broad range of observations and is unlikely ever to be falsified.

Written and checked against the IB Biology SL specification · Updated October 2026

Frequently asked questions

Why is Lamarckism not evolution?

Lamarckism claimed that characteristics acquired during an organism's life are inherited. Acquired changes, such as larger muscles from exercise, do not alter the genes in gametes, so they cannot be passed on. Evolution is change in the heritable characteristics of a population, so only genetic changes that are passed to the next generation count.

How does DNA provide evidence for evolution?

Comparing base sequences of DNA, or amino acid sequences of proteins, shows how related species are. Mutations accumulate in each lineage after it splits, so species with fewer differences shared a common ancestor more recently. These relationships mostly match those found from anatomy, which is independent, strong evidence of common ancestry.

What is the difference between homologous and analogous structures?

Homologous structures share the same basic structure because they were inherited from a common ancestor, but they may have different functions, like the pentadactyl limbs of humans, bats and whales. Analogous structures have the same function but different origins, produced by convergent evolution, like the wings of birds and insects.

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