Natural selection
Introduced| English | Meaning |
|---|---|
| natural selection/ˈnætʃərəl sɪˈlekʃn/ | The process in which inherited traits that improve survival and reproduction become more common in a population over generations. |
| competition/ˌkɒmpəˈtɪʃn/ | Rivalry between organisms, people or businesses for limited resources or opportunities. |
| evolution/ɪvəˈluːʃn/ | evolution |
Survival of the fittest
- Why do organisms become so well suited to their environment?
- The answer is natural selection 自然选择 — Darwin's great idea.
Put the steps of natural selection in order.
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Variation → competition → survival → inheritance.
Natural selection is often summarised as "survival of the ______".
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The best-adapted survive and reproduce.
The steps of natural selection
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- Variation: individuals in a species differ.
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- Competition 竞争: more are born than can survive; they compete for resources.
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- Survival: those with helpful features are more likely to survive and reproduce.
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- Inheritance: they pass on the helpful alleles, so the species changes over time.
Natural selection: the best-adapted survive, reproduce and pass on their alleles
Natural selection
Individuals best suited to their environment survive and pass on their genes — so the population changes over time.
Antibiotic resistance evolves because:
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Selection favours the already-resistant bacteria.
A classic example
- Antibiotic resistance: a few bacteria happen to have a resistance allele.
- Antibiotics kill the rest, the resistant ones survive and multiply — a resistant population evolves.
Natural selection
Run the generations: birds eat the moths that stand out, so the camouflaged ones survive and breed — the population shifts to match the forest.
Over many generations, natural selection leads to:
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Allele frequencies shift, changing the species.
Organisms develop helpful variations because they need them to survive.
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False. Variation arises randomly, mainly through mutation; organisms do not choose to adapt. Natural selection then favours the helpful variations.
Evolution 进化
- Over many generations, natural selection causes evolution — a change in a species.
- Helpful alleles become more common; unhelpful ones become rarer.
Organisms don't choose to adapt. Variation arises randomly (by mutation). Natural selection simply favours whichever variations already help survival. Nothing is deciding to change.
You've got it
- natural selection: variation → competition → survival of the fittest → inheritance
- helpful alleles are passed on, so the species changes — evolution
- antibiotic resistance is natural selection in action; variation is random, not chosen
Write from resistant bacteria again
- Bacteria vary, and a few resist an antibiotic.
- The survivors reproduce.
What process is this, and was the variation planned?
Selection acts on variation that is already there.
Antibiotic resistance spreading in bacteria is an example of what?
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The antibiotic selects the resistant survivors.