SPEC 4.6.3.1 – 4.6.3.3 · BIOLOGY ONLY · PAPER 2
Theory of Evolution, Speciation & Understanding of Genetics
The history-of-science lesson. Darwin's three observations. Why his theory was slow to accept. Lamarck, Wallace, and Mendel — what each one actually did, and how the four-stage timeline built modern gene theory.
Why This Lesson Matters
This is the history of science behind everything else in Module 6. Biology-only, Paper 2. It looks easy because there are no Punnett squares — but examiner reports say students consistently mess it up.
6
Marks On A
Recent 6-Marker
L3
Rarely Achieved
By Students
4
Named Scientists
You Must Know
Where Students Lose Marks
On the recent 6-marker, examiners noted that most students could write about fossils, but their explanation of how genetics has contributed to understanding evolution was weak or absent. The Mendel → chromosomes → DNA chain is what separates Level 2 from Level 3. That gap is what this lesson fixes.
Darwin's Three Observations
Charles Darwin made observations on a round-the-world expedition (HMS Beagle), backed by years of experimentation and developing knowledge of geology and fossils. He proposed the theory of evolution by natural selection, published in On the Origin of Species (1859).
1
Variation. Individual organisms within a particular species show a wide range of variation for a characteristic.
2
Survival. Individuals with characteristics most suited to the environment are more likely to survive to breed successfully.
3
Inheritance. The characteristics that enabled these individuals to survive are then passed on to the next generation.
Don't confuse with 6.06
These three observations (4.6.3.1) are different from the four-step natural selection chain (4.6.2.2, taught in lesson 6.06: variation → survive → reproduce → pass on alleles). The four-step chain is the mechanism; these three observations are what Darwin actually noticed that led him to that mechanism. Match the question — if it asks for Darwin's theory or observations, use these three; if it asks how natural selection works, use the four-step chain.
Why The Theory Was Slow To Accept
Darwin's ideas were controversial and gradually accepted. The spec lists exactly three reasons — you need all three for a complete answer.
1
Religious challenge. The theory challenged the idea that God made all the animals and plants that live on Earth. (Note: a study of creationism is not required by the spec.)
2
Insufficient evidence. There was not enough evidence at the time the theory was published to convince many scientists.
3
Mechanism unknown. The mechanism of inheritance and variation was not known until 50 years after the theory was published. Darwin couldn't explain how characteristics were passed on.
Today
The theory is now widely accepted because of: fossil evidence, genetic evidence (DNA), and observable natural selection (antibiotic resistance — Module 3 link).
Lamarck's Alternative Theory
Before — and alongside — Darwin, Jean-Baptiste Lamarck proposed an entirely different theory of how species change. The spec requires you to know his theory, why it's different from Darwin's, and why we now reject it.
Lamarck's Theory
Changes that occur in an organism during its lifetime can be inherited. Classic example: a giraffe stretches its neck reaching for leaves, so its offspring are born with longer necks.
Lamarck (wrong)
Acquired changes during life are passed on. The giraffe stretched its neck → its calf has a longer neck.
Darwin (correct)
Inherited variation already exists. Giraffes with longer-neck alleles survived better, reproduced more, and passed those alleles on.
Why Lamarck is wrong
Only changes to the DNA in gametes are inherited. Changes to body cells during your lifetime (muscle from gym, callouses on hands, a stretched neck) do not alter your gametes — so they aren't passed on. The spec wording: "in the vast majority of cases this type of inheritance cannot occur."
Wallace: The Other Scientist
Past Paper 2 questions test whether students know both scientists who developed natural selection. Spelling and pairing matter — naming Darwin alone is not enough.
Alfred Russel Wallace
Independently proposed the theory of evolution by natural selection. He worked worldwide gathering evidence — especially in the Amazon and Indonesia.
YearWhat Happened
1858Wallace published joint writings with Darwin , which prompted Darwin to publish ...
1859Darwin's On the Origin of Species appeared the following year.
Wallace is best known for
Warning colouration in animals (bright colours signalling that an animal is poisonous or dangerous).
The theory of speciation — his pioneering work led to our modern understanding.
Impact on biology (4.6.3.2 spec requirement)
The spec asks you to explain the impact of these ideas on biology. Darwin and Wallace's theory became the unifying framework for biology — every later field (genetics, ecology, medicine, conservation) builds on it. It explained the diversity of life, the relationship between species, why antibiotic resistance arises, and why selective breeding works. The theory of speciation has continued to develop over time as new evidence (fossils, DNA comparisons) has refined it.
The 5-Step Speciation Mechanism
A species is a group that can interbreed to produce fertile offspring. Speciation = the formation of a new species. The spec requires you to describe the steps that give rise to new species.
1
Isolation. Two populations of one species become geographically isolated (e.g. by a mountain range, river, or new island).
2
Variation. Each population shows genetic variation from random mutations.
3
Different selection pressures. The two environments differ — so different alleles become advantageous in each.
4
Natural selection diverges. Different alleles are passed on in each population over many generations.
5
New species. The two populations become so different that, even if reunited, they can no longer interbreed to produce fertile offspring — two new species have formed.
The Four Named Scientists
Past papers test scientist names directly. These four are the only ones the spec lists for 4.6.3.1–4.6.3.3. Memorise the spellings and the one-line contribution for each.
CHARLES DARWIN
Theory of evolution by natural selection
On the Origin of Species (1859). Round-the-world expedition. Three observations: variation, survival, inheritance.
ALFRED WALLACE
Independent co-discoverer of natural selection
Joint paper with Darwin in 1858. Famous for warning colouration and the theory of speciation.
JEAN-BAPTISTE LAMARCK
Rejected alternative theory
Proposed that changes during an organism's lifetime can be inherited. Now known to be wrong in the vast majority of cases.
GREGOR MENDEL
Father of genetics
Mid-19th-century monk who did breeding experiments on plants. Discovered inheritance "units" — now called genes.
Mendel's Breeding Experiments
Mendel is the start of the genetics half of this lesson. Spec ref 4.6.3.3. Students lose marks on recent 6-markers by skipping straight to DNA — Mendel comes first in the timeline.
Mendel's Key Observation
In the mid-19th century, Mendel carried out breeding experiments on plants and observed that the inheritance of each characteristic is determined by 'units' that are passed on to descendants unchanged.
What "units" became
Mendel's "units" are what we now call genes. He used the word "units" because genes, chromosomes, and DNA had not yet been discovered — he could only infer that something discrete must be doing the passing on, based on the ratios he observed in pea plants.
Spec wording to use
Use "units" when talking about Mendel's findings — not "genes." The terminology is historical, and AQA mark schemes award credit for "Mendel's description / idea of units / factors of inheritance".
Why Mendel Was Ignored In His Lifetime
The spec explicitly asks you to "understand why the importance of Mendel's discovery was not recognised until after his death."
1
The mechanism was unknown. Chromosomes had not been observed and DNA was unknown — so Mendel's "units" couldn't be linked to any visible structure inside cells.
2
The approach was unfamiliar. Mendel's mathematical / statistical way of working (looking at ratios in offspring) was new — biologists at the time weren't used to thinking that way.
3
The science caught up later. His work was rediscovered around 1900 — after his death — once chromosomes had been observed and could be linked to his units.
The Four-Stage Genetics Timeline
The spec lists exactly four stages in the development of genetics. Each stage adds one piece to gene theory. Memorise the order.
Mid-19th C
Mendel does plant breeding experiments → "units" passed unchanged.
Late 19th C
Chromosomes observed during cell division under microscopes.
Early 20th C
Chromosomes and Mendel's units behave similarly → "units" = genes on chromosomes.
Mid-20th C
DNA structure determined; mechanism of gene function worked out.
The Big Picture
This cumulative chain — Mendel's units → chromosomes → genes on chromosomes → DNA structure → protein synthesis — is what we call gene theory. The spec says it was "developed by many scientists" over roughly 100 years.
Practice Question
Extended-response — typical Paper 2 final question6 MARKS
The theory of evolution by natural selection is now widely accepted. Scientists' understanding of evolution has grown over the past 150 years from two main sources of evidence.
Discuss how each of the following has contributed to our current understanding of evolution:
the fossil record
the development of genetics , from Mendel to DNA.
Level 3 answer (5–6 marks). Must cover BOTH halves. Use mark-scheme vocabulary.
P
Fossils. Fossils show life existed in the past and show how species have changed over time. The fossil record provides evidence of extinction and shows how present-day organisms are related to past ones. Gaps in the record are being filled by new discoveries.
E
Mendel. In the mid-19th century, Mendel's breeding experiments with plants showed inheritance is determined by "units" / factors passed on unchanged — including dominant and recessive forms.
E
Chromosomes & DNA. In the late 19th century chromosome behaviour during cell division was observed and matched Mendel's units, so units were recognised as genes on chromosomes. In the mid-20th century the structure of DNA and the mechanism of gene function were worked out.
E
Mechanism. Genetic variation arises from mutations. Individuals with advantageous characteristics survive, reproduce, and pass on their alleles. Examples include antibiotic resistance in bacteria. New species form when populations diverge enough to stop interbreeding to produce fertile offspring.
Three Examiner Alerts
Alert 1 — Allele Language
When explaining what gets passed on during natural selection, write "alleles / genes / mutations" — never "characteristics" or "traits" or "genetic material". Examiner reports repeatedly flag students who write that advantageous characteristics or genetic information are passed on. The mark scheme only credits the named molecules. The word "alleles" earns the mark; "characteristics" does not.
Alert 2 — Speciation Needs "Fertile"
For speciation, write that the two populations can no longer interbreed "to produce fertile offspring". The MS is strict on the word fertile — some species can mate but produce sterile offspring (e.g. mules from horses × donkeys). Without "fertile" you cap the mark.
Alert 3 — Spell The Scientists Correctly
The four named scientists are Darwin, Wallace, Lamarck, Mendel. Common spelling errors include "Walace", "Lamark", "Mendell". Paper 2 has tested scientist names directly as 1-mark MCQ items — recent specimen papers ask students to identify which scientist proposed the (now-rejected) lifetime-inheritance theory (answer: Lamarck), and which two scientists proposed natural selection (answer: Darwin and Wallace). Get all four names right.
Common Errors To Avoid
Wrong
"Mendel discovered DNA."
Right
Mendel discovered inheritance "units" (now called genes). DNA structure was worked out ~85 years after Mendel's work.
Wrong
"Darwin worked alone and invented evolution."
Right
Darwin and Wallace independently developed natural selection. They published a joint paper in 1858.
Wrong
"Mendel was famous for his pea plants in his lifetime."
Right
Mendel's work was largely ignored during his lifetime — recognition came after his death, once chromosomes had been observed.
Wrong
"Giraffes stretched their necks, so their offspring had longer necks." (Lamarck-style)
Right
Giraffes with longer-neck alleles survived better and passed those alleles on. Acquired changes during life are not inherited.
Three Things To Remember
1
Darwin's Theory — Three Observations + Three Reasons
Three observations: variation → survival → inheritance. Slow to accept because of: religion, insufficient evidence, no mechanism (mechanism unknown for 50 years). Lamarck's lifetime-inheritance theory is the named alternative — wrong in the vast majority of cases.
2
Wallace + The 5-Step Speciation
Wallace independently proposed natural selection — joint paper 1858, Origin in 1859. Best known for warning colouration and speciation theory. Speciation: isolation → variation → different selection pressures → natural selection diverges → can no longer interbreed to produce fertile offspring.
3
The Four-Stage Genetics Timeline
Mid-19th Mendel's "units" → Late 19th chromosomes observed → Early 20th units = genes on chromosomes → Mid-20th DNA structure + protein synthesis worked out. Mendel ignored in his lifetime because the mechanism was unknown.
Summary
The Four Scientists — One Line Each
Darwin — three observations + On the Origin of Species (1859)
Wallace — independent co-discoverer; warning colouration; speciation
Lamarck — wrong alternative: lifetime changes inherited
Mendel — plant breeding; "units" = genes; ignored until after his death
Mark Scheme Vocabulary For Recent 6-Markers
"Units / factors of inheritance" (for Mendel) — not "genes"
"Pass on (advantageous) alleles / genes" — not "characteristics"
"Fertile offspring" (for speciation) — not just "offspring"
"Chromosome behaviour during cell division" — specific phrasing
Exam Tip
If a 6-marker asks about "the development of our understanding of evolution," structure your answer in two halves: (a) fossils — change over time, extinction, gaps being filled; (b) genetics — Mendel → chromosomes → DNA → variation from mutation → natural selection passes on alleles. Both halves must be present for Level 3.
Next: Why This Lesson Matters