Variation & Evolution (AQA GCSE Biology): Revision Notes
Darwin and Lamarck
The theory of evolution developed over many years using work from different scientists. Two key figures were Charles Darwin and Jean-Baptiste Lamarck, who had very different ideas about how evolution works.
Charles Darwin (1809-1882)
Charles Darwin came up with the theory of evolution by natural selection. He published his famous book On the Origin of Species in 1859. Darwin's theory revolutionised our understanding of how species change over time.
Darwin's Theory of Natural Selection has three main parts:
- Individual organisms vary - Animals and plants of the same species show differences in their characteristics
- The best survive and breed - Individuals with characteristics that help them survive in their environment are more likely to reproduce successfully
- Useful traits are inherited - The helpful characteristics that allowed parents to survive get passed on to their offspring
Timeline of Darwin's Revolutionary Work
Darwin's theory developed over many years through careful observation and research:
- 1831-1836: Darwin travelled on HMS Beagle and studied animals on the Galapagos Islands, including different types of finches
- 1837: Darwin presented his collection of specimens to the Zoological Society
- 1859: On the Origin of Species was published
- 1871: The Descent of Man was published
Why Darwin's ideas caused controversy
Darwin's theory was revolutionary and took time to be accepted. The scientific community and society needed time to understand and embrace these groundbreaking ideas.
Criticisms at the time:
- It challenged the religious belief that God created all living things
- There wasn't enough evidence to convince many scientists initially
- The mechanism of how traits are inherited wasn't understood (this was discovered 50 years later)
Why it was eventually accepted:
- Darwin's theory was based on careful scientific research
- He made detailed observations during his voyage on HMS Beagle
- He spent years conducting experiments and discussing with other scientists
- He used developing knowledge about fossils and geology
Jean-Baptiste Lamarck (1744-1829)
Lamarck had a different theory about evolution called inheritance of acquired characteristics. His approach to explaining evolutionary change was fundamentally different from Darwin's natural selection.
Lamarck's theory had two main parts:
- Use it or lose it - Body parts that are used a lot become bigger and stronger, while unused parts become smaller or disappear
- Pass it on - Changes that happen to an organism during its lifetime get passed to its children
Lamarck's Giraffe Neck Explanation
Lamarck would have explained long giraffe necks like this:
Step 1: A giraffe stretches its neck upwards to reach leaves on high branches Step 2: The giraffe's neck becomes longer because it's used so much Step 3: The giraffe's babies inherit the longer neck Step 4: Over time, giraffes develop increasingly long necks through this process
Why Lamarck's theory is wrong
We now know that Lamarck's theory is incorrect in most cases. Changes that happen to an organism during its lifetime cannot be inherited.
For example, if someone builds big muscles through exercise, their children won't automatically be born with big muscles. The key flaw is that Lamarck didn't understand that traits are determined by genes, not by how much body parts are used during an individual's lifetime.
Key Points to Remember:
- Darwin's theory: Evolution happens through natural selection - individuals with helpful traits survive and pass these traits to their offspring
- Timeline: Darwin developed his theory over decades, from his Beagle voyage (1831-1836) to publishing major books (1859, 1871)
- Initial controversy: Darwin's ideas were slowly accepted because they challenged religious beliefs and lacked supporting evidence at first
- Lamarck's theory: Evolution happens through inheritance of acquired characteristics - now known to be wrong in most cases
- Key difference: Darwin focused on natural selection of existing variations, while Lamarck thought organisms could change during their lifetime and pass these changes on