Darwin & Wallace

Darwin & Wallace

You already know HOW natural selection works. This module is about the two people who worked it out, and why almost nobody believed them at first. Remarkably, two naturalists on opposite sides of the world reached the same conclusion at almost the same time, without either one copying the other.

Darwin and the Beagle

Charles Darwin spent five years as a naturalist aboard HMS Beagle, collecting specimens and observations from around the world. On the Galapagos Islands he noticed that finches on different islands had different beaks, each suited to the food available there. A beak is a tool: a deep, blunt one crushes hard seeds, while a long, fine one reaches into places a heavy beak never could. Observations like these, gathered over roughly 20 years of thinking and testing, led him to evolution by natural selection.

Feed the finches

These four finches are identical apart from their beaks. Drag each food onto the beak best suited to getting it.

What the finches showed

Darwin found that finches on different Galapagos islands had differently shaped beaks. What did this suggest to him?

• Birds with beaks suited to the food on their island survived and reproduced, so the populations diverged
• Each finch grew a new beak shape to match its island during its lifetime
• Finches simply flew to whichever island matched the beak they already had
• Nothing about evolution, since beak shape is not inherited

Two men, one theory

Wallace was not Darwin's student, assistant or rival. He was a second naturalist who got to the same place from a different starting point, which is the whole reason the story matters:

How the theory emerged

Put the events in the development of the theory of evolution into order.

• Darwin sails on HMS Beagle and collects evidence, including the Galapagos finches
• He develops and tests the idea over about 20 years
• Wallace independently reaches the same conclusion and writes to Darwin
• Their work is presented jointly in 1858
• Darwin publishes On the Origin of Species in 1859
• The theory is gradually accepted as evidence and genetics catch up

Why nobody was convinced

The theory was published in 1859 and took decades to be widely accepted. Three reasons, and the third is the one that carries the marks: - It conflicted with religious belief about how life came to be, at a time when that belief was near-universal. - The evidence was thin at first. One naturalist's specimens and a book are not the mountain of fossil, anatomical and molecular evidence we have now. - Nobody knew how inheritance worked. Darwin could say offspring resemble their parents, but not WHY, or how variation arose in the first place. Without that, the mechanism had a hole in it. Mendel published his work on inheritance in 1866, and it went almost unnoticed until about 1900. Only when genetics arrived did the missing half of the explanation appear.

Why the slow acceptance?

Select ALL THREE reasons the theory of evolution was accepted only slowly.

• It conflicted with religious beliefs about how life was created
• There was not enough evidence at first to convince many scientists
• The mechanism of inheritance was not yet known
• The theory could not explain how one species might give rise to another
• Wallace publicly withdrew his support for the idea
• The fossil record showed no change at all in any species over time

Why does it matter that there were two?

Darwin and Wallace reached the same theory separately, from different species on opposite sides of the world. Why do scientists treat that as important?

• Two people reaching the same conclusion from different evidence makes it far less likely that either was mistaken
• Two scientists working on it meant the theory was finished twice as quickly
• It was important mainly so that credit could be shared fairly between them
• It proved the theory beyond any possible doubt

Mark the account

Here is part of a student's answer about the history of the theory. Tap the TWO sentences that are WRONG.

• Darwin collected evidence on a five-year voyage aboard HMS Beagle.
• Each finch changed the shape of its own beak during its lifetime to suit the food on its island.
• Alfred Russel Wallace reached the same theory while working in the Malay archipelago.
• Wallace served as Darwin's assistant on the Beagle and helped him collect the specimens.
• The theory was accepted only slowly, partly because nobody yet knew how inheritance worked.

Explain the delay

On the Origin of Species was published in 1859, but the theory of evolution by natural selection was not widely accepted by scientists for several decades. Explain why acceptance took so long.

• Give the religious objection, and say why it mattered so much at the time
• Say something about the amount of evidence available in 1859
• Explain the scientific gap: what could Darwin NOT account for?
• Say what later filled that gap, and roughly when

Story summary

Darwin collected evidence aboard HMS _____, including finches with beaks suited to different foods. _____ reached the same conclusion independently, and their work was presented jointly in 1858. Darwin published On the Origin of Species in _____. Acceptance was slow, above all because the mechanism of _____ was not yet known.