VMBO Year 3 · Inheritance and evolution · Section 3.6

Evolution

What is a species?

A useful definition for many sexually reproducing organisms is that members of the same species can reproduce together and produce fertile offspring. These offspring can themselves reproduce. This definition has limitations, especially for asexual organisms and fossils. Within a species, there can be different breeds or varieties, such as cultivated apple varieties with different flavours.

How does evolution work?

Evolution is change in inherited characteristics of populations over generations. Over long periods it can produce new species, while other species become extinct. Charles Darwin helped explain the role of natural selection. Modern evolutionary theory also includes genetic knowledge unavailable in Darwin's time.

Three processes important in this course are:

• Mutations, which can produce new alleles.
• Sexual reproduction, which reshuffles allele combinations.
• Natural selection, which changes the frequency of inherited characteristics through differences in reproductive success.

Variation within a population

A population consists of organisms of the same species in an area. Individuals differ genetically and in phenotype. Snails of one species, for example, can have different shell colours. Such variation means some individuals may be better suited to particular conditions.

Natural selection

Individuals with advantageous inherited characteristics, such as effective camouflage, may be more likely to survive and reproduce. They pass alleles to their offspring. Over generations, the advantageous variants can become more common. Individuals do not deliberately change their inherited characteristics because they need to adapt.

Example: snails

A shell colour that stands out against the surroundings may make a snail easier for predators to find. Better-camouflaged snails may leave more offspring. If conditions change, another shell colour may become advantageous. The outcome depends on the habitat, predators and other environmental factors.

How can a new species arise?

If groups become isolated, for example by a geographical barrier, gene exchange may decrease or stop. Mutations, selection and other processes can make the groups increasingly different. Eventually, they may no longer interbreed successfully, even if they meet again. This is speciation, often taking many generations. A barrier alone does not immediately create a new species.