KS3 natural selection and biodiversity: a guide for parents

Natural selection and biodiversity, explained

The starting point is variation: the individuals in a species are not identical. Some have characteristics that make them slightly better at finding food, escaping predators, resisting disease or attracting a mate. Organisms compete for limited resources, both with members of their own species and with other species, and more are born than can survive. Those with helpful characteristics are more likely to survive and reproduce, so they pass on the genes for those characteristics. Over many generations the helpful characteristics become more common in the population. This is natural selection, the idea set out by Charles Darwin and published in 1859.

Teachers emphasise two points. First, individuals do not change themselves to suit their environment during their lives; the change happens in the population over generations, because of inherited variation. Second, “fitness” here means being well adapted and leaving offspring, not being the strongest. Many schools use the peppered moth as their main example. In industrial areas of nineteenth-century Britain, soot darkened tree trunks, and dark moths were better hidden from birds than pale ones, so dark moths became much more common there. After pollution controls were introduced in the twentieth century and the air became cleaner, pale moths became common again.

Environmental change can also leave a species poorly adapted. If the climate shifts, a habitat is destroyed, a new predator or disease arrives or a competitor spreads, individuals with no helpful variation may fail to survive and reproduce. If no individuals in a species are well enough adapted to survive and reproduce, the species dies out. Extinction is the permanent loss of a species. Extinction is part of the long history of life, but human activities such as habitat loss, hunting and the movement of species have made it faster in recent times. Some schools also use bacteria as an example of selection in action: a few resist an antibiotic, survive treatment and multiply, which is why antibiotic resistance is a concern.

Biodiversity is the variety of living things in a habitat, region or on the whole Earth. A habitat with many different species tends to be more stable and better able to cope with disease or change. Biodiversity also gives us food, materials, medicines and clean water, and a wide range of genes in a species gives it more chance to adapt. Pupils are asked to explain why it is important to maintain it, and to suggest ways to do so, such as protecting habitats, controlling pollution and managing fishing and farming sustainably.

Gene banks are one way of preserving hereditary material. Seed banks store seeds from many plant varieties in cold, dry conditions, and some banks also freeze cells or sperm and eggs of rare animals. If a species or variety is lost from the wild, the stored material may later be used to restore it or to breed new varieties with useful traits such as resistance to disease.

Words your child will hear

Adaptation

A feature of an organism that helps it survive and reproduce in its environment.

Natural selection

The process in which better-adapted individuals survive and reproduce more, passing on their genes.

Competition

Organisms trying to get the same limited resources, such as food, light, water or mates.

Extinction

When every individual of a species has died, so the species no longer exists.

Biodiversity

The variety of different living things in a place or on Earth.

Gene bank

A store of seeds, cells or other material that keeps a species’ genetic information safe.

Resistance

The ability of an organism, such as a bacterium, to survive something that normally harms it.

What the National Curriculum says

The programme of study for Key Stage 3 says:

• Pupils should be taught that the variation between species and between individuals of the same species means some organisms compete more successfully, which can drive natural selection
• Pupils should be taught that changes in the environment may leave individuals within a species, and some entire species, less well adapted to compete successfully and reproduce, which in turn may lead to extinction
• Pupils should be taught about the importance of maintaining biodiversity and the use of gene banks to preserve hereditary material

Objectives from the National Curriculum in England, © Crown copyright, used under the Open Government Licence v3.0.

Try it: explaining natural selection step by step

Common mistakes and how to help

How to help at home

• Play a camouflage game. Cut about 40 small circles from a few colours of paper and scatter them over a patterned cloth or lawn. Give one player 20 seconds to “hunt” as many as possible. Count which colours survive most, repeat with the survivors, and discuss what happened.
• Look for adaptations on a walk. Notice how different animals and plants in your local park suit their habitats: webbed feet on ducks, thorns on brambles, thick bark on old trees. Ask what each feature helps the organism to do and what might happen if the environment changed.
• Count species in a small patch. Mark out one square metre of lawn, hedge bottom or park grass, well away from roads, and list every kind of plant and small animal you can find. Compare a mown patch with a wilder one to see how biodiversity differs.
• Save some seeds. Collect and dry seeds from garden flowers, such as marigolds, and keep them in labelled paper envelopes in a cool, dry place, away from pets and young children. This is a tiny version of a seed bank. Ask your child why storing different varieties is a good idea.

Related topics

Everything in Key Stage 3 science