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New observations and evidence to support the theory of evolution by natural selection continues to be found.

Repeated testing of a theory and finding more evidence to support it leads to the theory becoming more widely accepted amongst scientists.

Antibiotic resistance

Bacteria can evolve quickly because they reproduce at a fast rate. Mutations in the DNA of bacteria can produce new characteristics. A random mutation might cause some bacteria to become resistant to certain antibiotics, such as penicillin. Antibiotics usually kill bacteria, but in a case like this, the mutation means the bacteria cannot be destroyed by the antibiotic. The development of antibiotic resistance in bacteria gives more evidence to support the theory of natural selection leading to evolution.

Development of resistance

The main steps in the development of resistance are:

1. A random mutation occurs in a gene of an individual bacterial cell.
2. The mutation protects the bacterial cell from the effects of the antibiotic - it becomes antibiotic-resistant.
3. Bacteria without the mutation die or cannot reproduce when the antibiotic is present.
4. Antibiotic-resistant bacteria can reproduce with less competition from non-resistant bacterial strains - this is an advantage for them and these bacteria survive.
5. The genes for antibiotic resistance are passed to the offspring.
6. Over time the whole population of bacteria becomes antibiotic resistant because the antibiotic-resistant bacteria are best suited to their environment.

MRSA

The number of resistant strains has increased, partly due to the misuse of antibiotics. This has resulted in more infections that are difficult to control.

MRSA is methicillin-resistant Staphylococcus aureus. It is a very dangerous type of bacteria because it is resistant to most antibiotics, so if someone gets infected with MRSA they cannot be treated easily.

Explore the evidence for evolution with Dr Alex Lathbridge.

Listen to the full series on 91�ȱ� Sounds.