GCSE · Biology · Edexcel · Spec 1BI0

Darwin and Wallace and theory of evolution

Two scientists, working separately on different evidence, reached the same big idea. One of them got there partly by cross-breeding pigeons.

Four clues, one idea

Both men asked the same question: what makes the characteristics of species change over many generations? Tap each clue to see what it suggested.

1. Sloth fossils2. Galapagos finches3. Pigeon cross-breeding4. Wallace's boundaries5. Natural selection

Tap a cause to see what it triggered.

Biology · How natural selection works

Put natural selection in order

The order the steps of natural selection happen in

1 · First step5 · Last step

Inheritance
Advantageous traits are passed to offspring and become more common over generations.
Competition
Better adapted individuals compete more successfully for finite resources.
Variation
Individuals of a species have different traits.
Survival and reproduction
The better adapted individuals are more likely to survive and reproduce.
Advantage
Some of those traits give an advantage.

Biology · Two ideas that trip people up

Which idea is closest to yours?

Two friends are arguing about evolution. Pick the idea closest to what you think, say how sure you are, then see what it gets right or wrong.

Which is closest to what you think right now?

Evolution is just a theory, so it's only a guess.Darwin worked it all out on his own.It's a well-tested theory, and Darwin and Wallace each reached it independently.

How sure are you?

I'm sureI think soI'm guessing

Evolution is just a theory, so it's only a guess.

This is a common misconception

It's easy to see why this one sticks: in everyday speech, 'theory' can mean a hunch. In science it means something much stronger. A theory is a general explanation that applies to many situations and links many facts. The theory of evolution by natural selection has lots of supporting evidence, has been well tested and is widely accepted by most scientists, so it is very likely to be true. It is a well-supported explanation, not a guess.

Darwin worked it all out on his own.

This is a common misconception

Darwin's book is the famous part, which is why it feels like a one-man story. But Wallace came to the same conclusion independently. Wallace shared his idea with Darwin by letter, the two of them co-authored a scientific paper, and Darwin then published his book.

It's a well-tested theory, and Darwin and Wallace each reached it independently.

This matches the evidence

Yes. In science a theory is a well-supported explanation that links many facts, and two scientists looking at different evidence independently reached the same conclusion. That agreement is part of why the idea carries weight.

In science, 'theory' means a well-tested explanation linking many facts, and this one was reached independently by two scientists.

Why wasn't it accepted straight away?

Reason it through

Why was the theory not widely accepted at first, and why is it widely accepted now?

Link 1 of 4

First link · your turn

What did most people in the Western world believe about species in the 1800s?

Locked — reveal the link above first

Biology · Have a go

Explain it in your own words

Larger, harder beaks are found where there are hard seeds and nuts. Smaller, narrower beaks are found where there are fruit and insects.

Explain how natural selection could have produced the Galapagos finches' beaks that are specialised to their food. [5 marks]

Your answer

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

The mark scheme

Variation: individual finches of a species have different traits, such as different beaks. (1 mark)
Advantage: a beak that suits the available food gives a finch an advantage. (1 mark)
Competition: finches with a better suited beak compete more successfully for the finite food. (1 mark)
Survival and reproduction: those better adapted finches are more likely to survive and reproduce. (1 mark)
Inheritance: the advantageous beak trait is passed to offspring, so it becomes more common over generations. (1 mark)

Model answer

Finches of the same species have different traits, including differently shaped beaks (variation). Where one kind of food is available, a beak that suits it gives a finch an advantage. Finches with that better suited beak compete more successfully for the finite food. They are therefore more likely to survive and reproduce. The advantageous beak trait is passed to their offspring, so over many generations it becomes more common.

Whatever the example, walk through the same five steps: variation, advantage, competition, survival and reproduction, inheritance.

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

two scientists, one big idea

What you need to know

Evolution is when the characteristics of a species change over many generations, sometimes producing new species.
Natural selection is the theory that explains how: better adapted organisms are more likely to survive, reproduce and pass on their genes.
Have a goYour mate Sam says, "Natural selection means the strongest animals win." Which phrase from the bullet above should replace "strongest"?
"Better adapted to their environment".
It is about how well suited an organism is to its environment, not how strong it is, and even then better adapted organisms are only more likely, not certain, to survive and reproduce.
Darwin and Wallace were British scientists of the 1800s, when most people in the Western world believed species did not change.
Both asked the same question: what causes the characteristics of species to change over many generations?
Have a goMost people in the 1800s believed species did not change. Why does that make Darwin and Wallace's question a bold one?
It asked what makes species change, which most people believed they did not do.
Asking what causes characteristics to change over many generations only makes sense if species can change, and that went against the common belief.
Darwin's clues were fossils, finches and pigeons; Wallace's was how geographical boundaries such as rivers and mountain ranges separate species.
Have a goA classmate insists pigeons were Wallace's big clue. Are they right?
No. Pigeon cross-breeding was Darwin's clue.
Wallace's clue was how geographical boundaries such as rivers and mountain ranges separate species; Darwin used fossils, finches and pigeons.
They reached the same conclusion independently, then shared it through a letter, a joint paper and Darwin's book.
In science, a theory is a general explanation linking many facts, and this one is well tested and widely accepted.
It was not widely accepted at first; later work on inheritance and DNA explained how traits are passed on.

The big picture

Darwin and Wallace were British scientists of the 1800s who both asked what makes the characteristics of species change over many generations. Darwin followed fossils, finches and pigeons; Wallace followed how species are separated by geographical boundaries. Independently, they reached natural selection: better adapted organisms are more likely to survive, reproduce and pass on their traits. The theory was slow to be accepted until work on inheritance and DNA explained how traits are passed on.

Key points

1Evolution is the change in the characteristics of species over many generations; natural selection is the theory scientists use to explain it.

2Darwin's evidence came from fossils, Galapagos finches and pigeon cross-breeding; Wallace's came from species separated by geographical boundaries.

3Darwin and Wallace reached the same conclusion independently.

4A scientific theory is a well-tested explanation that links many facts, not a guess.

5Acceptance grew once work on inheritance and DNA explained how traits are passed to offspring.

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Worked example

Problem

Darwin found that an extinct giant ground sloth belonged to the same family as modern sloths. What can he conclude, and why does that count as evidence?

⚠ Watch out

Writing that the best adapted organisms always survive. The theory says better adapted organisms are more likely to survive, reproduce and pass on their genes, not that survival is guaranteed.

🧠

Memory hook

Darwin's clues: fossils, finches, pigeons. Wallace's clue: boundaries. Different evidence, same idea. And in the pigeon loft, humans did the choosing; in nature, the environment does.

✓

Check yourself

Close the page and list Darwin's three kinds of evidence, then Wallace's one, then the single conclusion they both reached.

Flashcards

(13)

What is evolution?

The process in which the characteristics of species change over many generations, sometimes becoming new species.

What is natural selection?

The theory scientists use to explain how and why evolution occurs: better adapted organisms are more likely to survive, reproduce and pass on their genes.

What did most people in the Western world believe about species in the 1800s?

That species did not change over time.

What question did Darwin and Wallace both try to answer?

What causes the characteristics of species to change over many generations?

What did the extinct giant ground sloth help Darwin understand?

That species were replaced by different versions over time.

What did the Galapagos finches' beaks lead Darwin to think?

That species are adapted to their environment and the best adapted are more likely to survive.

What did Darwin's pigeon cross-breeding experiments show?

That the characteristics of a species can be changed, so a similar process might happen in nature, with nature rather than humans shaping the changes.

What did Wallace notice about species and rivers or mountain ranges?

That different species were separated by geographical boundaries, which led him to think species are adapted to their unique environments.

What is artificial selection?

Selective breeding: humans choosing which organisms breed, which can change the characteristics of a species.

What are the five steps of natural selection?

Variation, advantage, competition, survival and reproduction, then inheritance.

What does "theory" mean in science?

A general explanation that applies to many situations and links many facts. Evolution by natural selection is well tested, well supported and widely accepted.

Why was the theory not widely accepted at first?

Partly because Darwin, Wallace and other scientists of the time could not explain how organisms pass on their traits to their offspring.

What later explained how traits are passed on?

Later work by many scientists on inheritance and DNA, which led to wider acceptance of the theory.

Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.

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Put natural selection in order

Which idea is closest to yours?

Explain it in your own words

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