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3.7.3
Evolution and Speciation
Analytical deep dive — question counts, mark distribution, mastery curves, command-word breakdowns, and examiner narrative analysis.
Questions
15
Total marks
50
Marks / Q
3.3
Accessibility
70.2%
Mastery
23.2%
Student strength
52.1%
01
At a glance
3.7.3 · Evolution and Speciation
8YRSYNTHESIS
3.7.3 (Evolution and Speciation) appeared in 7 of the 8 years between 2017 and 2024, contributing 15 questions and 50 marks across Papers 1, 2 and 3. APPLICATION dominates the mark distribution at 100.0% of total marks. The accessibility–mastery gap sits at 47.0 percentage points (70.2% vs 23.2%) — most students reach partial credit, but full marks remain harder to secure. The largest single question observed is worth 5 marks, signalling that AQA expects complete hierarchical accounts in this sub-section. Mastery varied year-to-year, lowest in 2018 (15.0%) and highest in 2024 (40.0%).
Access–mastery gap
+47 pp
Lowest mastery
2018 · 15.0%
Highest mastery
2024 · 40.0%
02
Question type split
By marks · compound to dominant
50MARKS
50
marks
Application100.0%50 marks
Knowledge0.0%0 marks
Calculation0.0%0 marks
(by marks; compound rows assigned to dominant type):
03
Credit terms — quick reference
Mark scheme tier-locked
20TERMS
Tier 1 · Always credit
mutationreproductive isolationfertile offspringgene flowallopatric speciation
Tier 2 · Sometimes credit
allelesdisruptive selectiongeographical isolationselection pressuresallele frequency
Reject · Never credit
allopatric speciation mechanisms onlygenes instead of allelesasexual reproductionmutation is not harmful/is beneficialmutation caused by drinking milk; LP gene (not allele); alleles surviving and reproducing'more alleles' alone (insufficient for frequency mark)gene frequencies (must say allele frequencies)inbreedingsympatricno inbreeding
04
Question patterns
Recurring formats & tariff structure
0PARAGRAPHS
05
Year-over-year presence
P1 + P3 · 2017–2024
8YEARS
| Year | Questions | Total marks | Mean accessibility | Mean mastery |
|---|---|---|---|---|
| 2017 | 2 | 7 | 61.5% | 17.5% |
| 2018 | 2 | 6 | 60.0% | 15.0% |
| 2019 | 0 | 0 | — COVID | — COVID |
| 2020 | 5 | 15 | — COVID | — COVID |
| 2021 | 2 | 5 | — COVID | — COVID |
| 2022 | 1 | 5 | 60.0% | 20.0% |
| 2023 | 1 | 5 | 82.0% | 21.0% |
| 2024 | 2 | 7 | 88.5% | 40.0% |
06
Mark scheme intelligence
2017–2024 mark scheme corpus
25TERMS
Tier 1 — frequently credited
| Term | Times credited | Years | Notes |
|---|---|---|---|
| mutation | 7 | 2017, 2018, 2021, 2022, 2023, 2024 | |
| reproductive isolation | 6 | 2017, 2020, 2021, 2022, 2023, 2024 | |
| fertile offspring | 4 | 2017, 2020, 2022, 2023 | |
| gene flow | 3 | 2017, 2021, 2022 | |
| allopatric speciation | 3 | 2021, 2022, 2023 |
Tier 2 — sometimes credited
| Term | Times credited | Years | Notes |
|---|---|---|---|
| alleles | 2 | 2017, 2020 | |
| disruptive selection | 2 | 2017, 2024 | |
| geographical isolation | 2 | 2022, 2023 | |
| selection pressures | 2 | 2022, 2023 | |
| allele frequency | 2 | 2022, 2023 |
Commonly rejected language
| Term | Times rejected | Years | Why rejected |
|---|---|---|---|
| allopatric speciation mechanisms only | 1 | 2017 | |
| genes instead of alleles | 1 | 2017 | |
| asexual reproduction | 1 | 2017 | |
| mutation is not harmful/is beneficial | 1 | 2017 | |
| mutation caused by drinking milk; LP gene (not allele); alleles surviving and reproducing | 1 | 2018 | |
| 'more alleles' alone (insufficient for frequency mark) | 1 | 2020 | |
| gene frequencies (must say allele frequencies) | 1 | 2020 | |
| inbreeding | 1 | 2020 | |
| sympatric | 1 | 2022 | |
| no inbreeding | 1 | 2022 | |
| 'mutate to adapt'; 'different altitudes' alone for different selection pressures | 1 | 2023 | |
| hide without qualification | 1 | 2024 | |
| 'pass on alleles' alone | 1 | 2024 | |
| confusing predator with prey | 1 | 2024 | |
| 'mutate to adapt' | 1 | 2024 |
Marks in this sub-section are typically awarded for precise terminology and correct application of biological principles. Sequential mark schemes — where each mark requires building on the previous one — are common in multi-mark questions; stating the first step without progression rarely earns more than one mark. Calculation marks are typically split between method (correct setup and value extraction) and answer (accurate numerical result), allowing partial credit when arithmetic errors occur.
07
Where students lose marks
Examiner-anchored error patterns
3CASE STUDIES
Conceptual errors
- Sympatric speciation question answered with allopatric mechanisms only — in 2017, when asked to describe sympatric speciation in a plant population, a significant number of students described geographical isolation and the formation of separate gene pools; this is the allopatric pathway; sympatric speciation occurs within a shared habitat via reproductive isolation mechanisms such as polyploidy or disruptive selection without physical separation; answers restricted to allopatric mechanisms were capped at a maximum of 3 marks out of 5 (2017 P2 Q09.1)
- Late-onset allele persistence explained without linking to age of reproduction — in 2017, stating that a mutation "is not harmful" or "is beneficial" was rejected; the mark required explaining that the allele for late-onset Alzheimer's disease does not reduce reproductive success because carriers reproduce before symptoms emerge at age 49; the reasoning must connect symptom onset to reproductive lifespan, not just assert that the mutation is neutral (2017 P2 Q10.2)
- "Mutation caused by drinking milk" proposed as mechanism for LP allele — in 2018, this was explicitly rejected; the correct account is that a pre-existing mutation conferring lactase persistence already existed in the population, and individuals carrying the allele survived and reproduced at higher rates in milk-drinking cultures; mutations are random events, not acquired in response to diet (2018 P2 Q09.1)
- Dominant allele confused as rising by reverting recessive alleles to dominant — in 2018, students suggested that the LP allele increased because recessive alleles "mutated back" to dominant; this misrepresents both dominance and mutation; the allele rose because heterozygotes expressed the phenotype and had a selective advantage, not because allele conversions occurred (2018 P2 Q09.2)
Vocabulary errors
- "Genes" used instead of "alleles" when describing what selection acts on — in 2017, "genes instead of alleles" was a listed rejection; selection acts on allele frequencies within the gene pool, not on genes as loci; using "gene" loses the critical distinction between the locus and the variant at that locus (2017 P2 Q09.1)
- "Gene frequencies" written instead of "allele frequencies" — in 2020, "gene frequencies" was rejected where the mark scheme required "allele frequencies"; this error was systematic enough to list as a rejection criterion; the distinction matters because a gene is a locus, while an allele is one of the alternative forms at that locus (2020)
- "Mutate to adapt" used to link mutation to natural selection — in both 2023 and 2024, "mutate to adapt" was rejected; this phrase implies directed mutation in response to environmental pressure, which contradicts the mechanism; mutation is random and undirected; natural selection then acts on the resulting variation; stating both steps separately avoids the disqualifying phrase (2023 P2 Q05.3, 2024 P2 Q10.3)
Application errors
- Allopatric speciation sequence stated without using the specific figure — in 2022, when a map of separated populations was given, examiners noted that the best answers referenced the river shown in the figure as the geographic barrier; generic descriptions of physical separation without anchoring to the provided context scored lower than answers that named the relevant feature from the stimulus (2022 P2 Q05.1)
- Reproductive isolation omitted as the final step in speciation — in 2022 and 2023, students who described geographical isolation and allele frequency divergence but stopped before stating that reproductive isolation meant the populations could no longer interbreed to produce fertile offspring lost the final mark; reproductive isolation is the defining criterion for speciation and must be stated explicitly (2022 P2 Q05.1, 2023 P2 Q05.3)
- "Different altitudes" given as distinct selection pressure rather than as context — in 2023, when populations overlapped across an altitude gradient, students who wrote "different altitudes alone" for different selection pressures were rejected; the mark required identifying what specifically differed at those altitudes (temperature, prey type, light intensity) and how that acted as a selection pressure, not just naming the altitude difference itself (2023 P2 Q05.3)
High-impact failures · examiner narrative
2017 P2 Q09.15 marks
Sympatric speciation in a plant population. Fewer than 2% of students scored full marks. The question specified sympatric speciation, but the majority of students described allopatric mechanisms — geographical isolation, separate gene pools formed by physical barriers. These answers were capped at 3 marks. Students who scored well anchored their answers to the same-habitat condition, described reproductive isolation via polyploidy or behavioural mechanisms, and explained how allele frequencies diverged without geographic separation. The examiner identified "genes" written instead of "alleles" as an additional source of mark loss distinct from the speciation type error.
2018 P2 Q09.14 marks
Natural selection acting on the LP allele in a milk-drinking population. Fewer than 13% of students scored more than 2 marks. The most common errors were: proposing that drinking milk caused the mutation; using "LP gene" rather than "LP allele"; describing alleles as "surviving and reproducing" rather than the individuals carrying them; and omitting directional selection as the mechanism. The mark scheme required a complete chain: random mutation → carriers had selective advantage in milk-dependent environments → LP allele frequency increased over generations via directional selection.
2024 P2 Q10.35 marks
Sympatric speciation in gecko populations sharing the same habitat. Only 3% of students scored all five marks. The two most common disqualifying errors were using "mutate to adapt" (rejected for implying directed mutation) and referencing sample size or statistical significance in an answer that was not asking for evaluation. Students who scored well named "same habitat" as the anchor for sympatric, described disruptive selection acting on colour variants, explained how reproductive isolation arose from mate preference, and stated that allele frequencies diverged until interbreeding no longer produced fertile offspring.
08
Difficulty signals
Performance metric synthesis
47PP GAP
Mean accessibility
70.2%
Mean mastery
23.2%
Mean student strength
52.1%
The accessibility–mastery gap of 47.0 percentage points characterises this sub-section's difficulty profile. Most students reach partial credit; full marks remain harder to achieve. Within 3.7 (Genetics, populations, evolution and ecosystems), 3.7.3 ranks 1 of 4 sub-sections by mean mastery (1 = hardest). Mastery trajectory is rising across the cohort window: 17.5% in 2017 → 40.0% in 2024 (+22.5 percentage points). Mean mastery was lowest in 2018 (15.0%) and highest in 2024 (40.0%).