Adaptation increases survival or reproductive success when a heritable trait improves performance under specific environmental conditions in evolving populations in evolving populations.
Coverage 2017–2024 · Updated 16 Jul 2026
Biological fitness is a genotype's relative contribution of surviving, reproducing offspring to the next generation in a particular environment.
Intraspecific competition exposes differences in adaptation. Survival has evolutionary importance when it increases reproductive opportunity, and reproduction passes the responsible alleles onward.
Compare individuals in the same population: adaptation to current conditions → survival and mating differences → different numbers of fertile offspring → different fitness.
A genotype that survives well but produces no fertile offspring has lower fitness than a competing genotype that leaves many reproducing descendants.
Fitness does not mean strength, health or lifespan in isolation; it is relative, environment-dependent reproductive success.
This objective is assessed through multiple choice, commonly using Outline / Compare / Describe.
Outline / Compare / Describe
Build the answer around this relationship: Adaptations are heritable traits that improve performance in context.
Representative question
In a natural population, what is a feature of individuals that are better adapted?
They start to produce offspring at a younger age than less well adapted individuals.
They produce identical offspring by cloning that are also better adapted.
They tend to produce more offspring during their lifetime than less well adapted individuals.
They do not produce more offspring than the environment can support.
Core D4.1 examples follow the same causal route: heritable variation exists, a selection pressure acts, individuals differ in fitness, and alleles linked to higher reproduction become more common. Endler’s guppies and sexual selection are evidence versions of the same chain.
Core natural-selection exam answers should never stop at “the best adapted survive.” They need the chain: heritable variation exists, a named pressure acts, some individuals have higher fitness, and their alleles become more common over generations. Use this for abiotic pressure, overproduction, sexual selection, and Endler-style data.
