Natural selection
Individuals in a population vary, some of that variation is inherited, and individuals with helpful traits leave more offspring. Over generations those traits become more common.
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Analogy
A sieve that lets helpful traits through more often.
In practice
Bacteria with a gene for antibiotic resistance survive treatment and multiply, so resistance spreads.
Practice
Flashcards
- What are the three conditions for natural selection?Variation in traits, inheritance of those traits, and different reproductive success.
Interview questions
- Explain how natural selection can cause antibiotic resistance to spread in a bacterial population.
- Variation: some bacteria carry a resistance mutation
- Antibiotic kills susceptible bacteria
- Resistant survive and reproduce
- Allele frequency rises over generations
Questions people ask
What does theory mean in the theory of evolution?
In science, a theory is a well-tested explanation backed by many lines of evidence, not a guess. The theory of evolution by natural selection is supported by fossils, genetics and direct observation. It is as well-established as the germ theory of disease or plate tectonics.
Does natural selection make organisms better or perfect?
No. Selection favours traits that help in the current environment, and only picks from the variation that exists. It cannot plan ahead, and trade-offs are common. A trait that helps in one place may be harmful elsewhere, and environments change, so no organism is perfect.