1.8.3Inquiry Process
Convergent Evolution — IB Biology HL Revision Notes & Topical Questions
5 min read 6 parts Lesson 29 of 160
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Section 1 of 6Convergent Evolution
Definition
- Definition Unrelated or distantly related species evolve similar adaptations because they face similar selection pressures.
Analogous structures
- Analogous structures Features with similar function but different evolutionary origin, such as the wings of birds and insects.
Homologous structures
- Homologous structures Features with a shared origin that may differ in function, such as the arm of a human and the flipper of a whale.
Selection pressure
- Selection pressure Similar demands of the habitat favour similar solutions, even from different starting points.
Section 2 of 6Examples
Such features show that the environment shapes organisms.
Examples
Streamlined bodies
- Streamlined bodies Sharks (fish), dolphins (mammals) and extinct ichthyosaurs (reptiles) all have a torpedo shape for fast swimming.
Camera eyes
- Camera eyes Octopuses and vertebrates both have complex eyes with a lens, but they develop differently.
Cactus and euphorbia
- Cactus and euphorbia Plants in American and African deserts have thick succulent stems and spines, though they belong to different families.
Moles
- Moles The Australian marsupial mole and the placental mole look similar and both dig underground.
Section 3 of 6Distinguishing Types of Evolution
1
Compare the structure and development of the feature in each organism.
2
If the underlying structure is different, the feature probably arose independently.
3
Check the evolutionary tree to see how far apart the species are.
4
Distant relatives with similar features suggest convergent evolution.
5
Close relatives with different features suggest divergent evolution from a shared ancestor.
| Type | Ancestry | Function | Example |
|---|---|---|---|
| Homologous | Shared | Different | Human arm, bat wing |
| Analogous | Different | Similar | Bat wing, insect wing |
Section 4 of 6Why Convergence Matters
Effect of habitat
- Effect of habitat Aquatic, aerial and burrowing environments each favour streamlined bodies, wings or strong digging limbs.
Evidence for selection
- Evidence for selection Repeated evolution of similar features shows natural selection can produce predictable solutions.
Classification risk
- Classification risk Looking only at appearance would wrongly group convergent organisms, so DNA is used to check.
Parallel with divergence
- Parallel with divergence Divergence produces different forms from one ancestor, while convergence produces similar forms from different ancestors.
| Evolution type | Starting point | Outcome |
|---|---|---|
| Convergent | Different ancestors | Similar features |
| Divergent | One ancestor | Different features |
Section 5 of 6Worked Example
Question
- The wings of a bat and the wings of an insect both allow flight but have different structure.
- State whether they are homologous or analogous and name the process involved.
- Compare structurea bat wing has bones and skin, while an insect wing is made of chitin with no bones.
- They do not come from a shared ancestral wing, so they are not homologous.
- Similar function arising from similar selection pressure makes them analogous structures.
Answer The wings are analogous and are the product of convergent evolution.
Section 6 of 6Exam Checklist & Tips
1.8.3 – Key Points for the Exam
- Convergent evolution Independent evolution of similar traits in unrelated lineages.
- Analogous Similar in function but not in origin.
- Divergent evolution Related species becoming more different.
- Selection pressure An environmental factor that affects survival and reproduction.
Common Mistakes
- Using analogous structures as evidence of close relationship.
- Thinking convergent organisms share a recent ancestor.
- Saying organisms evolve similar features because they need them.
- Mixing up convergent and divergent evolution.
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