Mutation, Selection And Speciation¶
Evolution content becomes clearer when it is treated as a chain rather than as separate definitions. New alleles arise by mutation. Sexual reproduction reshuffles alleles. Natural selection acts on phenotypes. Over time, allele frequencies change, populations diverge, and speciation can follow if gene flow stops.
The Chain At A Glance¶
| Stage | Main role | Why it matters |
|---|---|---|
| Mutation | Creates new alleles | Provides the ultimate source of genetic novelty |
| Meiosis and fertilisation | Reshuffle alleles into new combinations | Increase variation between individuals |
| Natural selection | Favours some phenotypes over others | Changes allele frequencies across generations |
| Hardy-Weinberg analysis | Provides a null model of no evolution | Helps detect when allele frequencies are changing |
| Isolation and divergence | Prevent gene flow between populations | Allows different alleles and adaptations to accumulate |
| Speciation | Produces reproductively isolated populations | Marks the formation of new species |
From Genes To Populations¶
- Mutation happens in DNA within individual organisms.
- Selection acts on phenotype, not directly on isolated genes.
- The evolutionary consequence is population-level change in allele frequency.
- Individuals do not evolve during their lifetime. Populations evolve across generations.
Why Hardy-Weinberg Matters¶
- It predicts allele and genotype frequencies if no evolutionary forces are acting.
- If observed frequencies differ persistently from those expectations, the population is not in equilibrium.
- This makes it useful as a test for whether evolution is occurring rather than as a mechanism that causes change.
Where Speciation Enters¶
- If populations become separated, gene flow is reduced or stopped.
- Different mutations, different selection pressures and different allele frequencies can then accumulate.
- Once reproductive isolation is established, the populations are treated as separate species.
Common Confusions¶
- Mutation does not happen because an organism needs it.
- Meiosis creates new combinations of alleles, but it does not create new alleles by itself.
- Natural selection does not change an individual's genes; it changes which alleles become more common in the population.
- Speciation is not just "lots of variation". Reproductive isolation is the key step.