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Theory of Evolution

Evidence for Darwin's theory of evolution


Fossils of ammonites - sea creatures that became extinct about 65 million years ago

Most of the evidence for evolution comes from the fossil record. Fossils show how much, or how little, organisms have changed over time.

One of the problems with the fossil record is that it contains gaps. Not all organisms fossilise well. And many fossils are destroyed by the movements of the Earth, or have simply not been discovered.

Peppered moths

Before the Industrial Revolution in Britain, most peppered moths were of the pale variety. They were camouflaged against the pale birch trees they rested on. Moths with a mutant black colouring were spotted easily by birds and eaten. This gave the white variety an advantage, making them more likely to survive and reproduce.

Airborne pollution in industrial areas blackened the birch tree bark with soot. This meant the mutant black moths were now camouflaged, while the white variety became more vulnerable to predators. It gave the black variety an advantage. They were then more likely to survive and reproduce. Over time, the black peppered moths became far more numerous in urban areas than the pale variety.

The pale peppered moths camouflage well against the pale birch tree

The darker mutant peppered moths camouflage well against the blackened birch tree

Antibiotic-resistant bacteria

E. coli bacteria (Photo from Rocky Mountain Laboratories, NIAID, NIH)

Micro-organisms such as bacteria [bacteria: Single-celled microorganisms, some of which are pathogenic in humans, animals and plants. Singular is bacterium. ] and viruses [viruses: ultramicroscopic non-cellular organisms that replicate themselves inside the cells of living hosts ] reproduce rapidly and can evolve in a relatively short time. One example is the bacterium E. coli. Its DNA [DNA: The material inside the nucleus of cells, carrying genetic information. DNA stands for Deoxyribonucleic Acid. ] can be damaged or changed during replication, and most of the time this causes the death of the cell. But occasionally the mutation is beneficial (to the bacteria). For example, it may allow resistance to certain antibiotics [antibiotics: Substances that kill bacteria. ]. When those antibiotics are present, the resistant bacteria have an advantage over the bacteria that are not resistant. Antibiotic-resistant strains of bacteria are an increasing problem in hospitals.


Scientists can now examine the DNA from different species of organism and use the data produced to see how closely related the two species are to each other. By collecting a lot of this data, scientists can compare the results with conventional ideas about how organisms have evolved. What they found was that DNA data supported the conventional theory of evolution.

Ideas about science

Developing explanations - higher only

You need to be able to provide an explanation that links together things that were previously thought to be unrelated. For example, DNA data being used to support the theory of evolution. Also people had noticed that there was a wide variety of different things living on the planet. Darwin noticed that different islands in the Galapagos had different types of finches adapted to eating the type of food found on each island. It was only when Darwin produced his theory of evolution by natural selection that these two unrelated facts were linked together.

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