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Variation, natural selection and extinction
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No two people are exactly alike. These differences help explain how species change over time.
Variation
Variation means differences between individuals of the same species.
Continuous variation: can be any value in a range, such as height or mass. Shown on a histogram.
Discontinuous variation: falls into separate groups, such as blood group. Shown on a bar chart.
Variation can be caused by genes, by the environment (diet, scars, language), or by both (height depends on genes and diet).
Continuous variation: can be any value in a range, such as height or mass. Shown on a histogram.
Discontinuous variation: falls into separate groups, such as blood group. Shown on a bar chart.
Variation can be caused by genes, by the environment (diet, scars, language), or by both (height depends on genes and diet).
Natural selection
Charles Darwin explained how species change in his book of 1859, *On the Origin of Species*.
1. Individuals in a species vary.
2. They compete for food, mates and space.
3. Those best adapted to the environment are more likely to survive and reproduce.
4. They pass on their genes, so the useful characteristics become more common over many generations.
1. Individuals in a species vary.
2. They compete for food, mates and space.
3. Those best adapted to the environment are more likely to survive and reproduce.
4. They pass on their genes, so the useful characteristics become more common over many generations.
Extinction and gene banks
If the environment changes (a new disease, a new predator, climate change, habitat loss) and a species cannot adapt fast enough, it may become extinct: none are left.
To protect biodiversity, scientists store genetic material in gene banks: seeds in seed banks (such as the Millennium Seed Bank at Kew), and frozen sperm, eggs and tissue. These could be used to bring back varieties in the future.
To protect biodiversity, scientists store genetic material in gene banks: seeds in seed banks (such as the Millennium Seed Bank at Kew), and frozen sperm, eggs and tissue. These could be used to bring back varieties in the future.
Rabbits vary in how fast they can run. Explain how foxes could cause rabbits to become faster over many generations.
- Faster rabbits are more likely to escape foxes and survive.
- They are more likely to breed and pass on their genes.
- Over many generations, more of the population has the genes for speed.
Answer: Faster rabbits survive and breed more, passing on their genes, so the population becomes faster over time.
Continuous variation is any value in a range (histogram); discontinuous variation is in groups (bar chart). Variation comes from genes and the environment. Natural selection: variation, competition, survival of the best adapted, genes passed on. Gene banks protect biodiversity.
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