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Evolution by natural selection
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Charles Darwin explained how species change over many generations. Antibiotic-resistant bacteria show evolution happening today.
Natural selection
1. There is variation within a population.
2. There is competition for food, mates and space.
3. Individuals with advantageous characteristics are more likely to survive and reproduce.
4. They pass on the alleles for those characteristics.
5. Over many generations, the characteristic becomes more common.
2. There is competition for food, mates and space.
3. Individuals with advantageous characteristics are more likely to survive and reproduce.
4. They pass on the alleles for those characteristics.
5. Over many generations, the characteristic becomes more common.
Antibiotic resistance
A random mutation makes one bacterium resistant to an antibiotic.
The antibiotic kills the others, so the resistant one survives and reproduces.
Soon most of the population is resistant. MRSA is an example.
The antibiotic kills the others, so the resistant one survives and reproduces.
Soon most of the population is resistant. MRSA is an example.
Evidence
Fossils show how organisms changed over time.
Antibiotic resistance shows evolution happening fast.
Darwin published *On the Origin of Species* in 1859. Alfred Russel Wallace independently developed the same idea.
Antibiotic resistance shows evolution happening fast.
Darwin published *On the Origin of Species* in 1859. Alfred Russel Wallace independently developed the same idea.
Explain why cheetahs became fast runners.
- Some cheetahs were faster than others (variation).
- Faster ones caught more prey, so survived and reproduced more.
- They passed on the alleles for speed.
- Over many generations, the population became faster.
Answer: By natural selection.
Variation, competition, survival of the best adapted, reproduction, and passing on alleles: repeated over many generations. Antibiotic resistance is evolution we can see.
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