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Lamarck's theory is wrong because only changes to the DNA in reproductive cells can be inherited. Free GCSE Edexcel Biology notes and 12 questions answered.
Comparing Theories of Evolution is part of The development of understanding of genetics and evolution in GCSE Edexcel Higher Biology.
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Lamarck's theory is wrong because only changes to the DNA in reproductive cells can be inherited. Free GCSE Edexcel Biology notes and 12 questions answered.
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Use this lesson to stay inside The development of understanding of genetics and evolution while connecting the detail back to the wider Topic 4: Natural selection and genetic modification topic.
Read the core explanations from Comparing Theories of Evolution before testing yourself from memory.
Why do giraffes have long necks? This simple question sparked one of science's biggest debates. Two brilliant scientists came up with completely different answers - and only one turned out to be right.
Understanding these competing theories isn't just about history. It's about how science works - how we test ideas, gather evidence, and sometimes discover that our first explanation was wrong.
Jean-Baptiste Lamarck proposed his theory in 1809. His big idea was simple: if you use a body part more, it gets stronger and bigger. If you don't use it, it shrinks. Most importantly, these changes get passed to your children.
Think of a blacksmith's muscular arms from years of hammering. Lamarck believed the blacksmith's children would inherit stronger arms. Or consider giraffes stretching their necks to reach high leaves - their offspring would be born with longer necks.
Trap: Many students think this sounds logical because we see changes during our lifetime. But there's a crucial difference between what happens to our bodies and what gets passed to our children through our genes.
Charles Darwin had a different explanation. He noticed that individuals in a species vary naturally - some giraffes are born with slightly longer necks, others with shorter necks. This variation is random, not caused by stretching.
Here's Darwin's logic: giraffes with longer necks can reach more food. They're healthier, survive longer, and have more babies. Their long-neck genes get passed on. Short-necked giraffes struggle to find food and have fewer offspring.
Over many generations, long necks become more common in the population. The species evolves - not because individuals stretched their necks, but because nature 'selected' the individuals who were already born with longer necks.
The crucial difference lies in the source of variation. Lamarck thought organisms could change themselves during their lifetime and pass these changes on. Darwin realised that useful variations already exist in the population - natural selection just makes them more common.
Worked example: Comparing the Two Theories
A population of moths lives near a factory. Over time, tree bark becomes darker due to pollution. How would each theory explain the increase in dark-coloured moths?
Answer: Darwin's theory correctly explains this - dark moths were already present but became more common through natural selection, not because light moths changed colour during their lifetime.
Modern genetics has shown us exactly why that older theory doesn't work. The characteristics we pass to our children are determined by DNA in our reproductive cells (sperm and eggs). Changes to our body during life don't alter this DNA.
Think about it: if you lose a finger in an accident, your children aren't born missing that finger. If you learn to speak French, your children aren't born speaking French. Body changes and learned behaviours stay with the individual.
The DNA Rule: Only changes to the DNA in reproductive cells can be inherited. Changes to body cells (muscle, skin, brain) during life cannot be passed on.
Exam questions often ask you to compare these theories. The key is to focus on the mechanism - how each theory explains where variation comes from and how it's passed on.
For 6-mark questions, structure your answer: state both theories, explain the key difference, give an example, and conclude with why Darwin's theory is supported by modern evidence while Lamarck's is not.
Common Exam Mistake: Don't confuse the two theories. Lamarck = traits gained during life inherited. Darwin = natural selection of existing variation. Keep them separate in your mind and your answers.
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Move to the related lessons or back to the topic page when you need the wider sequence before exam-style practice.
Some giraffes are born with slightly longer necks due to random variation. These giraffes reach more food, survive longer and have more offspring, passing on their long-neck genes, so over many generations long necks become more common in the population.
The inheritance of acquired characteristics is Lamarck's idea that characteristics gained during an organism's lifetime through use or disuse can be inherited by offspring. Modern genetics shows this is wrong, because body changes during life do not alter the DNA in sperm and eggs.
Acquired characteristics cannot be inherited, because changes to body cells such as muscle, skin or brain during life do not alter the DNA in reproductive cells. Only changes to the DNA in sperm and eggs can be passed on.
Lamarck's theory, proposed in 1809, is the idea that characteristics acquired during an organism's lifetime through use or disuse can be inherited by offspring. For example, Lamarck believed giraffes stretching their necks to reach high leaves would have offspring born with longer necks.
The key difference is the source of variation. Lamarck thought organisms change during their lifetime and pass these acquired changes on. Darwin realised useful variations already exist in the population through random variation, and natural selection makes them more common.
Lamarck's theory is wrong because only changes to the DNA in reproductive cells can be inherited. Changes to body cells during life do not alter this DNA, so a person who loses a finger in an accident does not have children born missing that finger.
Jean-Baptiste Lamarck proposed his theory in 1809. His idea was that using a body part more makes it stronger and bigger, not using it makes it shrink, and these changes get passed to offspring.
Lamarck explained giraffes' long necks by saying giraffes stretched their necks to reach high leaves, and their offspring were then born with longer necks. Darwin instead said some giraffes were already born with longer necks and were more likely to survive and reproduce.
Lamarck would say light moths changed colour during their lifetime to match dark bark and passed this on. Darwin would say some moths were naturally born darker, survived better because they were camouflaged, and passed on dark-colour genes, which correctly explains the change.
Lamarck's blacksmith example is the idea that a blacksmith's muscular arms, built up from years of hammering, would be inherited by the blacksmith's children. This is wrong because changes to muscle cells during life cannot be passed on.
In Darwin's theory, variation already exists naturally in the population and is random, not caused by use or stretching. Natural selection then makes the useful variations more common over many generations.
Learned behaviour cannot be inherited: a person who learns to speak French does not have children born speaking French. Body changes and learned behaviours stay with the individual because they do not change the DNA in reproductive cells.