GCSE · Biology · AQA · Spec 8461

Theory of evolution (biology only)

Natural selection doesn't need a single organism to change. So what is doing the work? And why did it take people so long to accept it?

Natural selection in three stages

Read down the three stages. Tap any stage for the question that leads you on to the next one.

Predict, then check

Not every theory agrees about what gets passed on. Commit to an answer before you check.

Suppose an organism changes during its lifetime. Will that change be passed on to its offspring?

Your turn

Fix this answer

A student was asked how characteristics come to be passed on to the next generation. They wrote: "The organisms changed during their lives to suit the environment, and then they passed those changes on to their offspring."

The student has described Lamarck's idea, not natural selection. Rewrite the answer so that it correctly describes how natural selection leads to characteristics being passed on to the next generation. [3 marks]

0 words · your answer stays on this page and is not sent anywhere.

The story of the theory

Put Darwin's story in order

When it happened

1 · Earliest4 · Latest

  1. Darwin proposes the theory of evolution by natural selection

    Backed by years of experimentation and discussion, and linked to developing knowledge of geology and fossils.

  2. The mechanism of inheritance and variation becomes known

  3. Darwin makes observations on a round-the-world expedition

  4. Darwin publishes On the Origin of Species (1859)

    There was much controversy surrounding these revolutionary new ideas.

Why did acceptance take so long?

Three separate reasons, all feeding one outcome. Tap each number to see what it contributed.

1. Challenged an existing belief2. Not enough evidence yet3. Mechanism of inheritance unknown4. Only gradually accepted

Tap a cause to see what it triggered.

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

How Darwin's natural selection works, how it differs from the idea that lifetime changes are passed on, and why the theory took so long to be accepted.

What you need to know

  • Darwin proposed the theory of evolution by natural selection 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.
  • Natural selection, stage by stage: individuals within a species show a wide range of variation for a characteristic; those with characteristics most suited to the environment are more likely to survive to breed successfully; the characteristics that enabled them to survive are passed on to the next generation.
  • Darwin published his ideas in On the Origin of Species in 1859. There was much controversy surrounding these revolutionary new ideas.
  • The theory was only gradually accepted because it challenged the idea that God made all the animals and plants on Earth, because there was insufficient evidence at the time to convince many scientists, and because the mechanism of inheritance and variation wasn't known until 50 years after publication.
  • Other theories, including Lamarck's, are based mainly on the idea that changes during an organism's lifetime can be inherited. We now know that in the vast majority of cases this type of inheritance cannot occur.

The big picture

Darwin proposed the theory of evolution by natural selection after observations on a round-the-world expedition. Individuals in a species vary; those most suited to the environment are more likely to survive to breed; and the characteristics that enabled them to survive are passed on. He published On the Origin of Species in 1859, amid much controversy. The theory was only gradually accepted: it challenged the idea that God made all the animals and plants, evidence at the time couldn't convince many scientists, and the mechanism of inheritance and variation wasn't known for 50 years. Lamarck's theory says lifetime changes are inherited; in the vast majority of cases, they can't be.

Key points

1Natural selection starts with variation that already exists. No individual has to change.
2Being best suited makes an individual more likely to survive to breed. It doesn't guarantee survival, so avoid 'will survive'.
3What's passed on is the characteristics that enabled survival, not changes made during a lifetime.
4The order of the story: expedition observations, then the theory, then On the Origin of Species in 1859, then the mechanism of inheritance and variation 50 years later.
5Slow acceptance had three separate reasons: a challenged belief, too little evidence at the time, and an unknown mechanism of inheritance.

Worked example

Problem

Explain why Darwin's theory of evolution by natural selection was only gradually accepted. (3 marks)

⚠ Watch out

Writing natural selection as if an organism changes during its lifetime and then passes that change on. That's Lamarck's idea. In natural selection the variation is already there, and what's passed on is the characteristics that enabled individuals to survive.

🧠

Memory hook

Natural selection is VSP: Vary, Survive (to breed), Pass on. For why it caught on so slowly, think BEM: it challenged a Belief, there wasn't enough Evidence yet, and the Mechanism of inheritance was missing for 50 years.

✓

Check yourself

Explain, in your own words, why natural selection doesn't need any individual organism to change during its lifetime.

Flashcards

(12)
What led Darwin to propose the theory of evolution by natural selection?
Observations on a round-the-world expedition, backed by years of experimentation and discussion, and linked to developing knowledge of geology and fossils.
Natural selection starts from what, within a species?
A wide range of variation between individuals for a characteristic.
Which individuals are more likely to survive to breed successfully?
Those with characteristics most suited to the environment.
Under natural selection, what is passed on to the next generation?
The characteristics that enabled the individuals to survive.
Why 'more likely to survive' rather than 'will survive'?
Being best suited improves an individual's chances of surviving to breed. It doesn't guarantee it.
Where and when did Darwin publish his ideas?
In On the Origin of Species, in 1859.
How were Darwin's ideas received when they were published?
There was much controversy surrounding these revolutionary new ideas.
Darwin's theory clashed with which existing belief about living things?
That God created every animal and plant found on Earth.
Why weren't lots of scientists persuaded straight away?
In 1859, the evidence available fell short of what was needed to persuade them.
How long after publication was the mechanism of inheritance and variation known?
50 years.
What is Lamarck's theory mainly based on?
The idea that changes that occur in an organism during its lifetime can be inherited.
What do we now know about inheriting changes made during a lifetime?
In the vast majority of cases, this type of inheritance cannot occur.

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