Convergent evolution is caused by similar selection pressures acting independently on different evolutionary lineages. Natural selection favours similar adaptations when unrelated species occupy similar environments or ecological niches.
This concept is required at both SL and HL in A4.1 Evolution and speciation. It can be explained as a sequence:
- Mutations and sexual reproduction produce heritable variation within each population.
- Different species experience a similar environmental challenge, such as moving efficiently through water or surviving with limited water.
- Individuals with traits that improve survival and reproduction have greater fitness.
- Their advantageous alleles are passed to more offspring.
- Over many generations, the populations independently evolve similar functional adaptations.
| Factor | Role in convergent evolution | Example |
|---|---|---|
| Similar abiotic conditions | Create similar physical challenges | Desert plants experience heat and limited water |
| Similar ecological niches | Favour similar methods of feeding, movement or defence | Sharks and dolphins are streamlined for efficient swimming |
| Natural selection | Increases the frequency of advantageous heritable traits | Streamlined individuals may move with less resistance |
| Separate ancestry | Ensures the trait evolved independently | Sharks are fish, whereas dolphins are mammals |
Convergent evolution produces analogous structures: features with similar functions but different evolutionary origins. For example, bird wings and insect wings both enable flight, but their structures did not originate from the same ancestral wing.
A common misconception is that similar features always indicate close common ancestry. This is incorrect: similarity caused by convergent evolution does not make the structures homologous. Homologous structures share an evolutionary origin, although their functions may differ.
In an IB exam, an “explain” question requires a linked mechanism: similar selection pressures → differential survival and reproduction → increased frequency of advantageous heritable traits → similar adaptations evolving independently. Always identify the resulting structures as analogous and avoid saying that organisms evolve traits because they “need” them.
