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Unit 4: Human Variation and Evolution

11 dot points, in syllabus order. Each dot point has a focused answer, with exam-style questions and worked answers where available.

How does selection pressure reshape a population, and why does it sometimes favour the extremes and sometimes the average?

Explain natural selection as a mechanism of evolution and describe directional, stabilising and disruptive selection with reference to their effects on a population

Natural selection. The four conditions for selection, fitness and selection pressure, and how directional, stabilising and disruptive selection each shift a population's distribution.

7 min read →

Why do some traits come in clear-cut categories while others vary smoothly across a whole range?

Explain patterns of human variation, including multiple alleles, polygenic inheritance and sex linkage, and distinguish continuous from discontinuous variation

Patterns of variation. Multiple alleles using ABO blood groups, polygenic inheritance and continuous variation, sex-linked inheritance, and how to classify a trait as continuous or discontinuous.

8 min read →

How can chance alone change a population's genetics, and what does a population with no evolution look like?

Explain how genetic drift (including founder and bottleneck effects) and gene flow change allele frequencies, and use the Hardy-Weinberg principle to describe a non-evolving population

Chance and migration in evolution. Genetic drift with the founder and bottleneck effects, gene flow between populations, and how the Hardy-Weinberg principle defines a population that is not evolving.

8 min read →

How does one species split into two that can no longer interbreed?

Explain the process of speciation, including allopatric and sympatric speciation and the reproductive isolating mechanisms that maintain separate species

Speciation. The biological species concept, allopatric and sympatric speciation, and the pre-zygotic and post-zygotic reproductive isolating mechanisms that keep species separate.

7 min read →

How is the information that makes us different from one another stored and read in our DNA?

Describe the structure of DNA, the relationship between genes, alleles, genotype and phenotype, and how the genetic code underpins variation

Genetic basis of variation. DNA structure and base pairing, the meaning of gene, allele, locus, genotype and phenotype, and how the genetic code links DNA to proteins and to variation.

7 min read →

What anatomical trends mark the evolution of modern humans from earlier hominins?

Describe the major trends in hominin evolution, including bipedalism, brain size and tool use, with reference to key genera

Hominin evolution. Bipedalism and its skeletal adaptations, trends in brain size and dentition, tool use and culture, and the key hominin genera.

9 min read →

Where does the variation between individual humans actually come from?

Explain the genetic and environmental sources of variation within human populations, including mutation, meiosis and random fertilisation

Variation. Mutation as the source of new alleles, meiosis and random fertilisation, plus continuous, discontinuous and environmental variation.

8 min read →

What features do humans share with other primates, and where do we sit in the classification of life?

Describe the characteristics that define primates and the classification of humans, and explain how shared primate features indicate common ancestry

Primates. The defining primate characteristics linked to an arboreal ancestry, the classification of humans within the primates, and how shared features point to common ancestry.

6 min read →

How did modern humans come to populate the whole planet, and what does the evidence say about where we started?

Explain the Out of Africa hypothesis for the spread of modern humans, compare it with the multiregional hypothesis, and evaluate the supporting evidence

Spread of modern humans. The Out of Africa hypothesis and the migration of Homo sapiens, the contrasting multiregional hypothesis, and the fossil, genetic and mitochondrial DNA evidence.

7 min read →

How do the allele frequencies of a whole population change from one generation to the next?

Explain how natural selection, gene flow, genetic drift and mutation change allele frequencies in populations over time

Population genetics. Gene pools and allele frequency, natural selection, gene flow, genetic drift, mutation and speciation.

9 min read →

What different lines of evidence show that humans share ancestry with other species?

Evaluate the types of evidence for human evolution, including fossils, comparative anatomy, biochemistry and DNA

Evidence for evolution. Fossils and dating, comparative anatomy with homologous structures, and biochemical and DNA evidence.

8 min read →