CHARLES DARWIN proposed the theory of evolution by NATURAL SELECTION (1859, 'On the Origin of Species').
The mechanism has four key steps:
1. VARIATION — individuals in a population show variation in their characteristics.
2. STRUGGLE FOR SURVIVAL — organisms produce more offspring than can survive; resources are limited.
3. SURVIVAL OF THE FITTEST — individuals with advantageous characteristics are more likely to survive and reproduce.
4. INHERITANCE — the advantageous characteristics are passed to offspring (heritable variation).
Over many generations → alleles for advantageous traits become more common in the population → the population EVOLVES.
EXAMPLE — Peppered moth:
Before Industrial Revolution: light moths more common (camouflaged against pale bark).
After: soot darkened trees → dark moths better camouflaged → survived better → dark allele became more common.
Alfred Russel Wallace
ALFRED RUSSEL WALLACE independently developed a theory of evolution by natural selection at the same time as Darwin.
Wallace wrote to Darwin in 1858 with his ideas — Darwin realised Wallace had reached the same conclusions.
Both theories were presented together to the Linnean Society in 1858.
Darwin published 'On the Origin of Species' in 1859 — the most complete and evidenced account.
WALLACE'S CONTRIBUTIONS:
Wallace's work in South-East Asia — he noticed differences between species on different islands.
Developed ideas about natural selection from observations of wildlife in the Amazon and Malay Archipelago.
Wallace also pioneered ideas about biogeography — why different species live in different regions.
His concept of 'warning colouration' (aposematism) — bright colours warning predators of toxicity.
Why Darwin gets more credit:
Darwin had 20 years more data and evidence supporting the theory.
Darwin's book was much more detailed and comprehensive.
But Wallace's independent discovery strengthens confidence in the theory.
Why the Theory Was Controversial
Darwin's theory was initially CONTROVERSIAL for several reasons:
1. LACK OF MECHANISM:
Darwin didn't know HOW characteristics were inherited (genetics wasn't understood yet).
Mendel's work on inheritance was concurrent but unknown to Darwin.
2. RELIGIOUS OPPOSITION:
Conflicted with religious beliefs that species were created in their current form.
Implication that humans evolved from ape-like ancestors was particularly controversial.
3. INCOMPLETE FOSSIL RECORD:
In 1859, there were gaps in the fossil record — critics argued there was insufficient evidence.
Subsequent discoveries (e.g. transitional fossils like Archaeopteryx) provided more support.
WHY THE THEORY IS NOW ACCEPTED:
Genetics — discovered independently by Mendel, later integrated with evolution (Modern Synthesis).
DNA evidence — genetic similarities between species match evolutionary relationships.
Fossil record — many transitional fossils now found.
Observed evolution — antibiotic resistance, Galapagos finch beak changes seen in real time.
The scientific community accepts evolution as the best explanation for the diversity of life.
⚠️ Common Mistake
Natural selection does NOT mean animals consciously choose to evolve. Organisms don't 'try' to adapt — those with random variations that happen to be advantageous survive better and reproduce more. The environment SELECTS — organisms don't choose. Also: Darwin AND Wallace both developed the theory independently.
📌 Key Note
Natural selection: variation → struggle → survival of fittest → inheritance → evolution. Darwin and Wallace independently developed the theory. Darwin's book (1859) was the most comprehensive. Initially controversial: no known mechanism, religious opposition, incomplete fossils. Now supported by genetics, DNA evidence, fossil record, observed examples.
🎯 Matching Activity — Natural Selection Steps
Put the four steps of natural selection in the correct order. — drag the symbols on the right to match the component names on the left.
Step 1
Drop here
Step 2
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Step 3
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Step 4
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Survival of the fittest — individuals with advantageous traits survive and reproduce
Inheritance — advantageous traits passed to offspring, become more common over generations
Struggle for survival — more offspring produced than can survive, resources limited
Variation — individuals in a population show different characteristics
⭐ Higher Tier Only
Evaluate how evidence from DNA sequencing and protein analysis supports evolutionary relationships more reliably than morphology alone. Discuss the relative contributions of Darwin and Wallace. Explain how the modern evolutionary synthesis united Mendelian genetics with Darwinian natural selection. Evaluate how the mechanisms of evolution have been refined as new evidence has emerged.
🔬 Triple Science Only
Theory of evolution detail (4.6.3.3) is biology-only — Combined Science covers evolution and natural selection more briefly. Triple includes Darwin's mechanism in detail, Wallace's contribution, and why the theory was controversial and how it gained acceptance.
🎯 Test Yourself
Question 1 of 2
1. Which of the following best describes Alfred Russel Wallace's role in the theory of evolution?
2. Why was Darwin's theory of natural selection initially controversial?
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