outline the theory of evolution as a process leading to the formation of new species from pre-existing species over time, as a result of changes to gene pools from generation to generation

Evolution

Definition

Evolution is the change in the genetic composition of a population’s gene pool over successive generations, leading to the emergence of new species from pre‑existing ones.

Key Concepts

• Gene pool – the total set of alleles present in a population.
• Allele frequency – the proportion of a particular allele among all alleles at a locus.
• Natural selection – differential survival and reproduction of individuals based on phenotype.
• Genetic drift – random changes in allele frequencies, especially in small populations.
• Mutation – the ultimate source of new genetic variation.
• Gene flow – movement of alleles between populations.

Mechanisms of Evolution

The main mechanisms that alter allele frequencies are summarised in the table below.

Hardy–Weinberg Principle

The Hardy–Weinberg equation provides a null model for a non‑evolving population:

\$p^{2}+2pq+q^{2}=1\$

where p and q are the frequencies of two alleles at a locus. Deviations from this equilibrium indicate that one or more evolutionary mechanisms are acting.

Speciation

Speciation occurs when reproductive isolation prevents gene flow between two groups, allowing independent evolutionary trajectories.

1. Allopatric speciation – geographic separation leads to divergence.
2. Peripatric speciation – a small peripheral population becomes isolated.
3. Parapatric speciation – adjacent populations diverge despite limited gene flow.
4. Sympatric speciation – new species arise within the same geographic area, often via polyploidy or niche differentiation.

Evidence Supporting Evolution

• Fossil record – shows chronological succession of forms.
• Comparative anatomy – homologous structures indicate common ancestry.
• Embryology – similar early developmental stages across taxa.
• Molecular biology – DNA and protein sequence similarities.
• Observed instances of microevolution – e.g., antibiotic resistance.

Summary

Evolution is a continuous process driven by changes in allele frequencies within a gene pool. Natural selection, genetic drift, mutation, and gene flow act together over many generations, producing the diversity of life and the formation of new species.