Genetic diversity is the raw material for evolution. When environments change — due to climate shifts, disease, habitat alteration or introduced predators — populations with high genetic diversity are far more likely to survive and adapt.
Within any population, individuals carry slightly different versions of genes (called alleles). This variation means:
- Some individuals may already carry alleles that confer resistance to a new pathogen
- Some may tolerate higher temperatures or drought conditions better than others
- Over generations, natural selection can favour advantageous alleles, shifting the population’s traits
This is the mechanism of adaptive evolution — and it only works if variation exists.
When populations are small and isolated, related individuals breed together. This increases homozygosity (both alleles at a locus are identical), which:
- Exposes harmful recessive alleles
- Reduces fertility, immune function and survival
- Is called inbreeding depression
A genetically uniform population faces higher extinction risk under environmental change because:
- If all individuals share the same susceptibility to a disease, one outbreak can eliminate the population
- Without allelic variation, natural selection has nothing to act on
In small populations, random changes in allele frequency (genetic drift) can eliminate rare alleles entirely, permanently reducing diversity.
| Event | Description | Example |
|---|---|---|
| Bottleneck | Population crashes to a very small size | Cheetah after ice age; northern elephant seal |
| Founder effect | Small group establishes a new population | Island colonisations; reintroduced species |
Both events drastically reduce genetic diversity and are difficult to reverse without gene flow from other populations.
The mountain pygmy possum (Burramys parvus) exists in isolated alpine patches in Victoria and NSW. Ski resort development has fragmented its habitat, separating populations that previously interbred. This isolation has reduced genetic diversity and increased inbreeding, threatening the species’ ability to adapt to changing alpine conditions driven by climate change.
Conservation response: building ‘wildlife underpasses’ beneath ski runs to reconnect populations and restore gene flow.
Conservation programs should aim to:
1. Maintain large, connected populations to maximise gene flow
2. Use translocation to introduce new alleles into isolated populations
3. Establish gene banks to preserve genetic material from at-risk populations
4. Prioritise species with already low genetic diversity for urgent intervention
VCAA FOCUS: Examiners frequently ask students to explain why genetic diversity is important for species facing environmental change — not just to define it. Focus on the link between allelic variation → natural selection → adaptation → survival.
