AQA GCSE Biology

Revision Notes

6.3.1 Theory of Evolution

Darwin's Theory of Evolution

  • Charles Darwin, as a result of observations on a round-the-world expedition, backed by years of experimentation and discussion and linked to developing knowledge of geology and fossils, proposed the theory of evolution by natural selection
  • Evolution can be defined as the change in the frequency of a phenotype in a population over many generations
  • Darwin’s theory, very simply, is:
    • Individuals in a species show a wide range of variation caused by differences in genes
    • Individuals with characteristics most suited to the environment have a higher chance of survival and more chances to reproduce
    • Therefore these characteristics are passed to their offspring at a higher rate than those with characteristics less suited to survival
    • Over many generations, these beneficial characteristics become more common in the population and the species changes (the species evolves)
  • This idea of natural selection became known as ‘survival of the fittest’
  • Darwin published his ideas in his famous book, On the Origin of Species (1859)

Acceptance of Evolution

  • The theory of evolution by natural selection was only gradually accepted because:
    • There was much controversy surrounding these revolutionary new ideas
    • The theory challenged the idea that God made all the animals and plants that live on Earth
    • There was insufficient evidence at the time the theory was published to convince many scientists
    • The mechanism of inheritance and variation was not known until 50 years after the theory was published
    • The theory of evolution by natural selection developed over time and from information gathered by many scientists

Lamarck's Theory of Evolution

  • Another theory of evolution, developed at the start of the 19th century (before Darwin announced his theory), was that of French scientists Jean-Baptiste Lamarck
  • Lamarck’s theory was based mainly on the idea that changes that occur in an organism during its lifetime can be inherited
  • His theory involved two main ideas:
    • a characteristic that is used frequently by an organism becomes better and stronger, whereas a characteristic that isn’t used gradually disappears
    • the beneficial characteristics that are used frequently (and are improved as a result) are passed to offspring
  • For example, Lamarck suggested that:
    • Giraffes had a short-necked ancestor that would frequently stretch its neck to reach the high branches so it could feed on the leaves
    • This repeated stretching could very slowly elongate the giraffe’s neck and that this would be passed to the giraffe’s offspring
    • Over time and many generations, the giraffe would evolve to have the very long neck it has today
  • We now know that in the vast majority of cases this type of inheritance cannot occur and that Lamarck’s ideas were incorrect

Lamarck theory of evolution, downloadable IGCSE & GCSE Biology revision notes

An example demonstrating Lamarck’s ideas on evolution, which we now know are wrong

Exam Tip

There are many examples of natural selection but they ALL follow the same sequence described above:

  • Within a species, there is always variation and chance mutation
  • Some individuals will develop a phenotype (characteristic) that gives them a survival advantage and this allows them to:
    • live longer
    • breed more
    • be more likely to pass their genes on
  • Repeated over generations, the ‘mutated’ phenotype will become the norm

Remember, it is the concept you have to understand, not the specific example.

Author: Jenna

Jenna studied at Cardiff University before training to become a science teacher at the University of Bath specialising in Biology (although she loves teaching all three sciences at GCSE level!). Teaching is her passion, and with 10 years experience teaching across a wide range of specifications – from GCSE and A Level Biology in the UK to IGCSE and IB Biology internationally – she knows what is required to pass those Biology exams.

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