1.8.2Inquiry Process
Evidence of Evolution — IB Biology HL Revision Notes & Topical Questions
5 min read 6 parts Lesson 28 of 160
Part 1 of 6Lines of Evidence
Evolution is the change in the heritable characteristics of a population over successive generations.
Fossil record
- Fossils in rock layers show a sequence of forms through time, including transitional forms between groups.
Homologous structures
- Similar bone patterns in the limbs of different vertebrates point to inheritance from a common ancestor.
Molecular evidence
- The more recently two species diverged, the fewer differences in their DNA or protein sequences, such as cytochrome c.
Selective breeding
- Humans have produced very different forms, such as cabbage and kale from one wild plant, in a few thousand years.
Observed change
- Antibiotic resistance in bacteria and changes in beak size in finches show evolution happening within human lifetimes.
Part 2 of 6How Each Evidence Works
How Each Evidence Works
Fossils
- Dating by rock layers or radioisotopes gives the age and order of appearance of forms.
Homology
- Shared structure with different functions suggests modification of a common design by natural selection.
Sequences
- Similarities in universal genes such as cytochrome c measure how closely species are related.
Biogeography
- Island species resemble those on the nearest mainland, which suggests descent from colonists.
| Evidence | What it shows |
|---|---|
| Fossils | Change over time |
| Homology | Common ancestry |
| DNA differences | Degree of relatedness |
Part 3 of 6Strength of the Case
1
Independent lines of evidence from different sciences all give the same pattern.
2
Predictions from evolution, such as finding transitional fossils, have been confirmed by new discoveries.
3
DNA comparisons agree with relationships derived from anatomy and the fossil record.
4
Direct observation shows that natural selection changes populations rapidly.
5
Together these form a strongly supported scientific theory.
Part 4 of 6Worked Reasoning with Molecular Data
Reading differences
- A table of amino acid differences between species shows how many substitutions separated each pair.
Molecular clock
- If changes accumulate at a roughly steady rate, the number of differences estimates time since divergence.
Human and chimpanzee
- Their DNA sequences are about 98 to 99 percent identical, consistent with a recent common ancestor.
Limits of the clock
- Rates vary between genes and lineages, so estimates are checked against fossils.
| Species pair | Amino acid differences in cytochrome c |
|---|---|
| Human and chimpanzee | 0 |
| Human and rhesus monkey | 1 |
| Human and horse | 12 |
Part 5 of 6Worked Example
Question
- The forelimbs of a human, a whale and a bat all contain the same bones in a similar arrangement but are used for different purposes.
- Explain how this supports evolution.
- These are homologous structures, sharing the same underlying bone pattern.
- Such a pattern is explained by inheritance from a common ancestor with a pentadactyl limb.
- Natural selection then modified the limb differently in each lineage for grasping, swimming and flying.
- This is evidence for common descent with adaptation.
Answer Homologous limb structure shows the three species share a common ancestor, supporting evolution.
Part 6 of 6Exam Checklist & Tips
1.8.2 – Key Points for the Exam
- Evolution Change in heritable characteristics of a population over generations.
- Homologous structure A structure with the same origin but different function.
- Fossil Preserved remains of an ancient organism.
- Cytochrome c A protein used to compare species.
Common Mistakes
- Saying evolution is only a guess, ignoring the evidence.
- Stating that individuals evolve; populations evolve.
- Confusing homologous with analogous structures.
- Thinking evolution is directed towards a goal.
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