⛵ Observations
Darwin sailed round the world on the ship HMS Beagle, on an expedition that lasted from 1831 to 1836. He saw a huge range of plants and animals, and he noticed that similar living things differed slightly from place to place.
Understanding Genetics and Evolution » Darwin, Lamarck and the Theory of Evolution
What you'll learn this session
Study time: 30 minutes
AQA spec: 4.6.3.1 (biology only)
- How Darwin gathered evidence for his theory of evolution
- The three ideas in Darwin's theory
- Why the theory was only gradually accepted
- Lamarck's theory and why it is rejected
🔒 Unlock Full Course Content
Sign up to access the complete lesson and track your progress!
Unlock This CourseDarwin's big idea
Charles Darwin was a British scientist who proposed the theory of evolution by natural selection. A scientific theory is an explanation that is backed by evidence and can be tested. Darwin did not get his idea in a single flash. It grew over many years from what he saw, what he tested and what he discussed with other people.
He also did not work alone. His idea was linked to the developing knowledge of geology and fossils at the time, and it was built on information gathered by many scientists. This is how science often works: ideas develop over time as more evidence is collected.
Key terms:
- Theory of evolution: the idea that species change over a very long time, and new species develop from earlier ones.
- Controversy: a lot of public argument about an idea.
Where did Darwin's evidence come from?
🔬 Experiments and discussion
After he came home, Darwin spent years on experiments, such as breeding pigeons, and on discussing his ideas with other scientists. He did not rush to publish.
Darwin also used what was known about geology and fossils. Fossils showed that living things from the past were different from those alive today, and that rocks had built up over very long periods of time. This suggested that there had been plenty of time for living things to change gradually.
The three ideas in the theory
Darwin's theory of evolution by natural selection can be summed up in three linked ideas. You will meet how this process works in the lesson on evolution by natural selection.
- Individual organisms in a particular species show a wide range of variation for a characteristic.
- Individuals with characteristics most suited to the environment are more likely to survive to breed successfully.
- The characteristics that enabled these individuals to survive are then passed on to the next generation.
Remember
The theory has three parts: variation, survival of the best suited, and passing on those characteristics. If you can say these three ideas in order, you can describe Darwin's theory.
A controversial book
In 1859 Darwin published his ideas in a book called On the Origin of Species. There was much controversy surrounding these revolutionary new ideas. Many people were shocked, and the debate went on for a long time.
Why was the theory only gradually accepted?
Today, evolution by natural selection is accepted by almost all scientists. But in 1859 many people did not agree. There were three main reasons.
⛪ It challenged belief
The theory challenged the idea that God made all the animals and plants that live on Earth.
📄 Not enough evidence
There was insufficient evidence at the time the theory was published to convince many scientists.
❓ No mechanism
The mechanism of inheritance and variation was not known until 50 years after the theory was published.
The third reason matters a lot. Darwin said that useful characteristics are passed on, but nobody knew how characteristics were passed from parents to offspring, or why individuals varied. Without that, the theory had a gap in it. The discovery of how inheritance works came later and helped to convince scientists. You will see more in the lesson on Mendel and the discovery of genes.
Worked example
Question: A scientist in 1860 says, 'Darwin's theory cannot be right, because he cannot explain how a parent passes a feature to its young.' Which reason for slow acceptance is this?
Answer: The mechanism of inheritance and variation was not known.
Lamarck's theory
Darwin's theory was not the only one. Another scientist, Jean-Baptiste Lamarck, proposed a different theory. Lamarck's ideas were based mainly on the idea that changes that occur in an organism during its lifetime can be inherited.
🦒 Lamarck's idea
A famous example is the giraffe. Lamarck's idea was that a giraffe stretched its neck to reach high leaves, so its neck became a little longer. It then passed on that longer neck to its young.
🌿 Darwin's idea
Darwin's idea was different: giraffes with naturally longer necks were more likely to survive and breed.
Why is Lamarck's idea rejected?
We now know that, in the vast majority of cases, this type of inheritance cannot occur. A change that happens to your body during your lifetime does not change the characteristics you pass on to your children.
Common mistakes
Do not write that an animal changes during its life and then passes this on. A weightlifter who builds big muscles does not have children born with big muscles.
You do not need to study creationism for this course.
Exam-style question
(a) Darwin published his theory in 1859. Give two reasons why the theory was only gradually accepted. [2 marks]
(b) Lamarck suggested that changes made to an organism during its lifetime could be inherited. Explain why this idea is not accepted today. [2 marks]
Model answer
(a) Any two from: it challenged the idea that God made all the animals and plants (1); there was insufficient evidence at the time to convince many scientists (1); the mechanism of inheritance and variation was not known until 50 years later (1).
(b) We now know that in the vast majority of cases changes during an organism's lifetime cannot be inherited (1), so for example a parent's changed body does not change the characteristics of its offspring (1).
Exam tip
In part (a), do not just write 'people disagreed'. Use the real reasons: belief that God made living things, too little evidence, or inheritance not understood.