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D4.1.5—Differences in adaptation, survival, reproduction

Adaptation increases survival or reproductive success when a heritable trait improves performance under specific environmental conditions in evolving populations in evolving populations.

Syllabus
First assessment 2025
Objective
D4.1.5
Level
HL

Exam analysis

Chance of appearing2%of analysed past papers
Latest appearanceNovember 2024
Most common paperPaper1
Typical marks1–2

Common command terms

  • Outline
  • Compare
  • Describe

Recent exam appearances

November 2024Paper1 ["HL"] · TZ019[ 1 ]D4.1.5—Differences in adaptation, survival, reproduction
May 2017Paper3 ["HL"] · TZ21(b)[ 2 ]D4.1.5—Differences in adaptation, survival, reproduction

Coverage 2017–2024 · Updated 16 Jul 2026

Fitness Means Alleles Reaching Future Generations, Not Strength or Longevity Alone

Individual outcome Contribution to evolutionary fitness
survives but produces no surviving offspring little or none
reproduces early and offspring later breed high contribution
wins mates but offspring have low survival mating success may not become high lifetime fitness

Fitness is relative to a particular environment. A phenotype advantageous during drought may be neutral or costly when water is abundant.

Better adapted does not mean perfect. Selection compares variants currently present and is constrained by trade-offs, ancestry and chance.

Peppered-Moth Frequencies Changed When Camouflage Changed Survival

  1. The population already contained pale and melanic heritable forms.
  2. Soot darkened resting surfaces and reduced pale lichen cover in industrial areas.
  3. Birds more often detected the less-camouflaged form.
  4. Better-camouflaged moths survived and reproduced at a higher rate.
  5. The allele associated with that form increased locally across generations.

When air pollution later declined and lichens returned, the direction of the camouflage advantage could reverse. Fitness belongs to a phenotype–environment relationship, not permanently to one colour.

Pale and melanic peppered moth forms are shown side by side, with pale associated with non-polluted habitats and melanic with industrially polluted habitats.

Natural Selection Connects Variation, Environment and Reproduction Across Generations

mutation creates alleles + sexual reproduction reshuffles them → offspring vary → limited resources and abiotic or biotic pressures produce unequal survival and mating → heritable variants reach offspring unequally → population trait and allele frequencies change

Claim to test Evidence needed
adaptation occurred by selection heritable variation plus unequal reproductive contribution across generations
sexual selection acted trait differences predict mating success
environmental pressure caused change controlled manipulation or strong comparative evidence links pressure to fitness
population evolved heritable trait or allele frequency changed, not merely one individual

Avoid purpose-driven language. Populations do not create useful mutations on demand; selection filters inherited variation already produced by mutation and recombination.

Differences in adaptation, survival, reproduction

[ 1 ]

In a natural population, what is a feature of individuals that are better adapted?

Concept essentials

  • Adaptations are heritable traits that improve performance in context.
  • Evolution depends on reproductive success, not survival alone.
  • The value of a trait can change when the environment changes.