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

Natural and Artificial Selection

Learning Objective

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 their alleles to the next generation.

Key Concepts

• Variation – individuals within a population differ genetically.
• Over‑production – most species produce more offspring than can survive.
• Struggle for existence – competition for limited resources (food, shelter, mates).
• Survival of the fittest – those best suited to the environment 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; only a fraction survive.
3. Environmental pressures (predation, climate, disease, competition) create a “struggle for existence”.
4. Individuals possessing advantageous traits have higher survival and reproductive rates.
5. Advantageous alleles increase in frequency over generations.

Mathematical Representation of Allele Frequency Change

The change in frequency of a favourable allele (p) can be expressed as:

\$\Delta p = \frac{p(1-p)s}{1 - s p}\$

where s is the selection coefficient (0 < s < 1).

Examples of Natural Selection

• Industrial melanism in the peppered moth (Biston betularia).
• Antibiotic resistance in bacterial populations.
• Beak size variation in Darwin’s finches during drought periods.

Artificial Selection

Artificial selection is a process in which humans deliberately choose which individuals reproduce, based on traits that are desirable to us rather than those that increase survival in the wild.

• Selective breeding of dogs for temperament, size, or coat colour.
• Crop improvement – e.g., high‑yield wheat varieties.
• Laboratory selection of fruit flies for longer lifespan.

Comparison of Natural and Artificial Selection

Summary

Natural selection is a fundamental mechanism of evolution. It relies on the production of many offspring, competition for limited resources, and differential reproductive success based on genetic variation. Artificial selection mirrors the same principles but replaces environmental pressures with human choice, allowing rapid development of desired traits.