Evidence for Evolution - TCE Biology (Tasmania)
“Describe and evaluate the lines of evidence that support evolution.”
Multiple independent lines of evidence support evolution: the fossil record shows change over time, comparative anatomy reveals shared ancestry, biogeography links species to their geography, embryology shows common developmental patterns, and molecular data show that related species have more similar DNA and proteins.
TASC's Biology Level 3 course (BIO315124, current for 2026) expects you to understand that life on Earth has changed and diversified over time, but it does not list the lines of evidence for evolution (fossils, comparative anatomy, molecular evidence) as content, and they are not in the external assessment specifications. Treat this page as background. The examined evolution content is on natural selection, population genetics and speciation.
What this dot point is asking
Fossil evidence
Fossils are the preserved remains or traces of past organisms. Because fossils form in layers of sedimentary rock, deeper layers are generally older, allowing scientists to order them in time. The fossil record shows that life has changed over hundreds of millions of years, that many extinct species existed, and that simpler forms generally appear before more complex ones.
Transitional fossils are especially important because they show intermediate features between older and newer groups. Dating methods, including radiometric dating using the decay of isotopes, allow fossils and rock layers to be assigned absolute ages.
A transitional fossil shows a mix of features from an ancestral group and a more recent descendant group, providing direct evidence of evolutionary change between forms.
Comparative anatomy
Comparing the body structures of different species reveals patterns that point to common ancestry.
- Homologous structures have the same basic underlying structure but different functions, such as the pentadactyl (five-fingered) limb seen in humans, whales, bats, and cats. The shared plan indicates descent from a common ancestor, with divergent evolution adapting the limb to different uses.
- Analogous structures have similar functions but different underlying structure, such as the wings of insects and birds. These arise through convergent evolution, where unrelated species independently evolve similar solutions, and they do not indicate close relationship.
- Vestigial structures are reduced features that had a function in ancestors but little or none now, such as the human appendix or the pelvic bones of whales.
A human arm, a whale flipper, a bat wing, and a cat leg all contain the same arrangement of bones (humerus, radius, ulna, and digits) despite being used for grasping, swimming, flying, and walking. The most logical explanation is that all four inherited the limb plan from a shared ancestor and natural selection modified it for each environment. This is homology, strong evidence of common descent.
Biogeography
The geographic distribution of species supports evolution. Species on isolated land masses, such as Australia's marsupials, are often unique because they evolved separately after isolation. Islands frequently have closely related species derived from a single colonising ancestor, as Darwin observed with the finches of the Galapagos. Distribution patterns match the history of continental movement and isolation rather than random placement.
Embryology and development
Many vertebrate embryos show striking similarities early in development, such as pharyngeal (gill) arches and tails, even in species that look very different as adults. These shared developmental features reflect inherited genetic instructions from a common ancestor.
Molecular and biochemical evidence
Modern biology provides some of the strongest evidence. Comparing DNA sequences, amino acid sequences of proteins, and shared biochemical pathways shows that more closely related species have more similar molecules. The near-universal genetic code and shared molecules like cytochrome c indicate that all life shares a common origin.
Because mutations accumulate at a roughly steady rate over long periods, the number of differences between the DNA or proteins of two species estimates how long ago they shared a common ancestor. This idea is called the molecular clock and lets scientists build and date evolutionary trees.
Evaluating the evidence
No single line of evidence proves evolution alone, but the strength of the case comes from many independent sources all pointing to the same conclusion. Fossils, anatomy, biogeography, embryology, and molecular data are consistent with each other, which is why evolution is accepted as the unifying theory of biology.
Homologous structures (same structure, different function) indicate common ancestry and divergent evolution. Analogous structures (different structure, same function) result from convergent evolution and do not show close relationship. Confusing the two leads to wrong conclusions about how related two species are.
Exam-style questions
Questions in the style of TASC exam questions on this dot point, each with a worked answer. They are written by ExamExplained unless tagged "Past paper"; the year shows the paper a question is modelled on.
Original6 marksThe forelimbs of a human, a whale, a bat and a horse all contain the same set of bones arranged in the same basic pattern, despite being used for very different functions. Name this type of structure, explain what it suggests about the ancestry of these animals, and distinguish it from an analogous structure using an example.Show worked answer →
A 6 mark answer names homologous structures, draws the ancestry conclusion and contrasts with analogy.
- Structure type
- These are homologous structures: the same underlying bone pattern modified for different uses.
- What it suggests
- A shared basic plan modified for different functions indicates the animals share a common ancestor that had that limb plan. The structure diverged through divergent evolution as descendants adapted to different environments.
- Analogous structures (contrast)
- Analogous structures have a similar function but different underlying structure and no recent common ancestor, arising by convergent evolution. Example: the wing of an insect and the wing of a bird both allow flight but are built differently and evolved independently.
Markers reward naming homologous structures, the common-ancestor/divergent-evolution conclusion, and a correct analogous example linked to convergent evolution.
Original6 marksExplain how each of the following provides evidence for evolution: (a) the fossil record; (b) comparing the DNA or protein sequences of different species; (c) biogeography (the distribution of species such as marsupials in Australia). Evaluate which line of evidence is strongest and why.Show worked answer →
A 6 mark answer explains all three lines and makes a reasoned evaluation.
- (a) Fossil record
- Shows a sequence of forms over time, with transitional fossils linking groups; relative and absolute dating show simpler forms appear before more complex ones, supporting gradual change.
- (b) Molecular evidence
- The more similar two species' DNA or protein sequences are, the more recently they shared a common ancestor. Differences accumulate over time, so sequence comparisons reveal relationships and a molecular clock.
- (c) Biogeography
- Isolated regions such as Australia have unique groups (marsupials) because populations were isolated and evolved separately. Distribution reflects shared ancestry plus geographic isolation.
- Evaluation
- Molecular evidence is often considered strongest because it is quantitative, available for living species, and independently confirms relationships suggested by fossils and anatomy, reducing reliance on incomplete fossil preservation.
Markers reward a correct explanation of all three lines and a justified evaluation (any defensible choice with sound reasoning).