What different lines of evidence support the theory of evolution?
Evaluate the evidence for evolution from fossils, comparative anatomy, biochemistry and biogeography
A focused answer to the WACE Year 12 Biology dot point on evidence for evolution. Covers the fossil record, comparative anatomy and homologous structures, molecular and biochemical evidence, and biogeography with Australian examples.
Reviewed by: AI editorial process; not yet individually human-reviewed
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What this dot point is asking
SCSA wants you to describe each line of evidence, explain what it shows, and recognise that the strength of the theory comes from many independent lines pointing to the same conclusion. A strong answer links each type of evidence to common descent.
The fossil record
Fossils are the preserved remains or traces of past organisms. Arranged by the age of the rock layers in which they are found, they show that life has changed over time, with simpler forms in older rocks and more complex or modern forms in younger rocks. Transitional fossils, which show features intermediate between groups, document the gradual change from one form to another. The fossil record is incomplete because fossilisation is rare, but the patterns it does show are consistent with evolution.
Comparative anatomy
Comparing the body structures of different species reveals telling patterns.
- Homologous structures have the same basic underlying structure but different functions, such as the bone pattern shared by a human arm, a whale flipper and a bat wing. Their shared plan points to a common ancestor.
- Vestigial structures are reduced remnants of organs that were functional in ancestors, such as the pelvic bones of whales.
Biochemical and molecular evidence
All living things use DNA, the same genetic code, and many of the same proteins, which itself points to a common origin. More precisely, the more closely related two species are, the more similar their DNA and protein sequences. By comparing sequences such as cytochrome c or DNA itself, biologists can measure relatedness and build evolutionary trees. This molecular evidence often confirms relationships first suggested by anatomy.
Biogeography
Biogeography is the study of where organisms live and why. Isolated regions tend to have unique organisms found nowhere else, which makes sense if those organisms evolved in isolation from a few ancestral colonisers.
Why multiple lines matter
No single line of evidence proves evolution on its own; the strength of the theory comes from the agreement of many independent lines. Fossils show change over time, anatomy shows shared ancestry, biochemistry quantifies relatedness, and biogeography explains distribution. When evidence collected by different methods converges on the same conclusion of common descent, the explanation becomes very well supported.
Linking evidence to the mechanisms
The evidence for evolution and the mechanisms of evolution fit together. Natural selection, drift, gene flow and speciation explain how change happens; fossils, anatomy, biochemistry and biogeography are the record of that change having happened. Understanding both means you can explain not only that species share ancestry but how and why their gene pools diverged over time.
Exam-style practice questions
Practice questions written in the style of SCSA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
WACE 20216 marksExplain how homologous structures and molecular (biochemical) evidence each support the theory of common descent. Use an example for each.Show worked answer →
A 6 mark explain answer needs both lines defined, linked to common descent, with examples.
- Homologous structures
- These share the same underlying structural plan but may perform different functions. The pentadactyl (five-boned) limb of a human arm, a whale flipper and a bat wing has the same bone arrangement despite different uses. The shared plan is best explained by inheritance from a common ancestor whose descendants modified the limb for different roles.
- Molecular evidence
- All organisms use DNA and the same genetic code, and the more closely related two species are, the more similar their DNA and protein sequences. Comparing a conserved protein such as cytochrome c shows fewer differences between closely related species, allowing relatedness to be quantified and evolutionary trees to be built.
- Link
- Both lines point independently to common descent: shared structure and shared sequence are inherited from shared ancestors.
Markers reward a correct example for each line and an explicit link to inheritance from a common ancestor.
WACE 20235 marksAustralia has many unique organisms, such as marsupials and the platypus, that are found nowhere else. Explain how biogeography provides evidence for evolution, and why evidence from several independent fields strengthens the theory.Show worked answer →
A 5 mark answer needs the biogeography reasoning plus the multiple-lines point.
Biogeography. Australia separated from other landmasses and remained isolated for a long time. Organisms there evolved from ancestral colonisers without gene flow from other continents, so they diverged into unique forms (marsupials, monotremes) found only in Australia. This distribution is exactly what evolution in geographic isolation predicts, and is hard to explain if species were unchanging.
Multiple lines. No single line proves evolution alone, but fossils, comparative anatomy, biochemistry and biogeography are independent methods that converge on the same conclusion of common descent. Agreement between independent lines makes the theory very well supported.
Markers reward the isolation-and-divergence reasoning and the point that converging independent evidence strengthens the theory.