VMBO Year 2 · HAVO/VWO Years 2–3 · Inheritance and evolution · Section 5.4

The theory of evolution

Evolution

Evolution is change in inherited characteristics of populations over generations. It can lead to the appearance of new species, changes within existing species and extinction.

Some changes occur over many millions of years, while others can be observed over much shorter times. Charles Darwin developed an explanation based on inherited variation, natural selection and the origin of species. Modern genetics adds knowledge Darwin did not yet have.

Genetic variation

Mutation creates new genetic variants. Sexual reproduction reshuffles inherited variants into new combinations. These genetic differences can contribute to differences in phenotype.

Variation matters because some individuals may be better suited than others to a changing environment.

Natural selection

Organisms differ in their chances of survival and reproduction. In a particular environment, some inherited characteristics help individuals leave more offspring.

Those variants can become more common over generations. A familiar simplified example is selection favouring longer necks in giraffes where reaching food provides an advantage. Evolution does not occur because an individual stretches its neck and passes that acquired change to its offspring.

New species

Populations can change as variants associated with greater reproductive success become more common. More than one form may remain within a species, as variation within dog breeds illustrates.

New species arise when populations become sufficiently reproductively separated and diverge. Individuals do not deliberately change their inherited traits because they need to adapt.

Isolation

A river, mountain range or another barrier can separate populations and reduce reproduction between them. Different conditions, mutation, selection and chance can then lead to different genetic changes.

Over time, the groups may become unable to interbreed successfully under natural conditions. They can then be recognised as separate species.