explain that natural selection occurs because populations have the capacity to produce many offspring that compete for resources; in the ‘struggle for existence’, individuals that are best adapted are most likely to survive to reproduce and pass on t

Published by Patrick Mutisya · 8 days ago

Natural and Artificial Selection – A‑Level Biology 9700

Natural and Artificial Selection

Learning Objective

Explain that natural selection occurs because populations have the capacity to produce many offspring that compete for limited resources; in the “struggle for existence”, individuals that are best adapted are most likely to survive to reproduce and pass on their alleles to the next generation.

Key Concepts

  • Variation – individuals within a population differ in heritable traits.

  • Over‑production of offspring – most species produce more offspring than can survive.

  • Struggle for existence – competition for food, shelter, mates, etc.

  • Survival of the fittest – those with advantageous traits are more likely to survive.

  • Reproductive success – surviving individuals pass their alleles to the next generation.

Steps in Natural Selection

  1. Genetic variation arises through mutation, recombination, and gene flow.

  2. Population produces many offspring; resources are limited.

  3. Individuals compete for resources – the “struggle for existence”.

  4. Those with traits that confer a survival advantage are more likely to reach reproductive age.

  5. These individuals reproduce more successfully, increasing the frequency of advantageous alleles.

  6. Over many generations, the population becomes better adapted to its environment.

Suggested diagram: Flowchart of the natural selection process from variation to adaptation.

Mathematical Representation of Allele Frequency Change

The change in frequency of an allele \$A\$ after one generation of selection can be expressed as:

\$p' = \frac{p\,w_A}{\bar{w}}\$

where \$p\$ is the initial frequency of allele \$A\$, \$w_A\$ is the fitness of allele \$A\$, and \$\bar{w}\$ is the mean fitness of the population.

Artificial Selection

Artificial selection is a process in which humans intentionally select individuals with desirable traits to breed, thereby accelerating changes in allele frequencies.

  • Selection pressure is applied by humans rather than the natural environment.

  • Often involves a smaller gene pool and more rapid fixation of traits.

  • Examples: domestic dogs, crop varieties, laboratory fruit flies.

Comparison: Natural vs. Artificial Selection

AspectNatural SelectionArtificial Selection
Driving forceEnvironmental pressures (predation, climate, competition)Human preferences and goals
Selection agentSurvival and reproductive success in natureHuman breeders or researchers
Time scaleOften long (thousands to millions of years)Usually short (generations to decades)
Genetic diversityMaintained by balancing forces (mutation, gene flow)Can be reduced due to strong, directed selection
Typical outcomesAdaptations that increase fitness in a specific environmentTraits that may not enhance survival in the wild (e.g., exaggerated size)

Key Take‑aways

  • Populations produce many offspring, leading to competition for limited resources.

  • Individuals with traits that improve survival and reproduction are more likely to pass those traits to the next generation.

  • Natural selection is an unguided, environment‑driven process, whereas artificial selection is guided by human choice.

  • Both processes change allele frequencies, but the speed, direction, and outcomes can differ markedly.