Evidence for Evolution — Print · Grade 10 Science
Chapter: Evolution, Ancestry & BiodiversityEvidence for Evolution
Learning goals
- I can describe how fossils, comparative anatomy, embryology, molecular biology, and biogeography each provide evidence for evolution.
- I can explain why agreement among several independent lines of evidence makes the case for common ancestry so strong.
Readings for this unit
Before this unit
Compare anatomy, sequences and dated records.
Use three flexible study sessions: core explanation and Parts 1–2; Parts 3–4 with their reasoning checks and models; then the whole-unit application, worked examples, independent practice, and exit check. Allow about 50–60 minutes per session, including diagrams, data work, and notebook explanations. Attempt each check before opening its guidance. Schedule chapter investigations, review, and exams separately; add time where prerequisites are uncertain. Trace the explained visual parts and write a first model, then attempt the illustrated and changed independent cases. In the third session explain a correction and revise the opening account using evidence.
Start with something to explain
Why can similar function coexist with different ancestry?
Illustrative evidence case. Selected structures and sequences constrain different relationships, while fossil records add time with gaps.
Notice and wonder
Record two observations using the stated quantities or relationships. Keep observations separate from possible causes. Write one question that a new measurement could help answer.
Why can similar function coexist with different ancestry?
Your first model
Separate observed resemblance, defined characters and a relationship hypothesis.
Build the language from the idea
- homologous structures
- Body parts that share the same underlying anatomical plan because they were inherited from a common ancestor, even when they now perform different functions — such as the forelimbs of humans, whales, and bats.
- analogous structures
- Body parts that perform a similar function and may look alike but do not share a recent common origin — such as the wings of insects and birds — resulting from convergent evolution.
- vestigial structure
- A reduced, often nonfunctional structure that is a leftover of a fully functional feature in an ancestor, such as the human appendix or the internal hip bones of a whale.
- transitional fossil
- A fossil that shows a mix of traits from an ancestral group and its descendants, documenting change between forms — such as Tiktaalik, between fish and four-legged animals.
- biogeography
- The study of where species live and how they are distributed across the globe, which reflects their evolutionary history and the movement of the continents.
- molecular evidence
- Similarities in DNA, RNA, and protein sequences among species; the more recently two species shared an ancestor, the more alike their molecules tend to be.
No one was present to watch the whole history of life unfold, so how do we know evolution happened? The answer is the same way a detective solves a case without a video of the crime: by gathering many independent lines of evidence that all point to the same conclusion. For evolution, at least five separate kinds of evidence converge, and — crucially — they were discovered by different scientists using different tools, yet they tell the same story of common ancestry.
The first line is the fossil record. Read from deep, old rock to shallow, young rock, it shows life changing over hundreds of millions of years, and it preserves transitional fossils that capture change in the act. *Tiktaalik*, a 375-million-year-old fossil with fish-like scales and gills but also a neck and sturdy, limb-like fins, sits right between fish and the first four-legged land animals — and scientists predicted the age and location of the rocks to search in *before* they found it. A whole series of fossils likewise traces whales from four-legged land mammals to today's fully aquatic swimmers.
The second line is comparative anatomy. The forelimb of a human, the flipper of a whale, and the wing of a bat look completely different and do completely different jobs, yet inside each you find the very same bones in the very same arrangement — one upper-arm bone, two forearm bones, then wrist and finger bones. These homologous structures only make sense if all three species inherited that limb plan from a shared ancestor and then modified it. Contrast that with analogous structures, like a bird's wing and an insect's wing: both fly, but they are built on completely different plans, so their similarity reflects convergent evolution to a shared task, not shared ancestry. Even better clues are vestigial structures — the tiny hip bones buried inside whales, or the human appendix and tailbone — reduced leftovers that make sense only as inheritances from ancestors that used them.
The third line comes from comparative embryology. Very early in development, the embryos of fish, chickens, and humans look startlingly alike, and all of them grow pharyngeal arches in the throat region — structures that become gill supports in fish but are remodeled into parts of the jaw, ear, and throat in humans. Shared early development points to shared genetic instructions inherited from a common ancestor.
The fourth and arguably strongest line is molecular evidence. Every living thing on Earth — bacterium, mushroom, redwood, human — stores information in DNA and reads it with nearly the same genetic code, a unity that itself argues for a single origin of life. Better still, we can *count* the differences: the more recently two species share an ancestor, the more similar their DNA and protein sequences are. Humans and chimpanzees share about 98–99% of their DNA; humans and mice far less; humans and yeast less still. Remarkably, this molecular family tree matches the tree built from anatomy and fossils, even though the methods are completely independent.
The fifth line is biogeography — the geography of life. Oceanic islands like the Galápagos are home to unique species found nowhere else, and each most closely resembles species on the *nearest mainland*, exactly as expected if a few colonists arrived and then diverged. Australia, isolated for tens of millions of years, teems with marsupial mammals (kangaroos, koalas, wombats) filling roles that placental mammals fill elsewhere. When five independent lines of evidence — fossils, anatomy, embryology, molecules, and geography — all converge on the same branching tree of life, the case for evolution by common descent becomes about as strong as any conclusion in science.
Evidence for common ancestry includes shared anatomical patterns, fossils, development and molecular sequence relationships. Independent kinds of evidence strengthen an inference when they agree. A similar function alone can also arise through convergent evolution.
Homologous structures reflect inherited underlying relationships even when functions differ. Analogous functions do not by themselves establish close ancestry. Compare the pattern of parts and developmental or molecular evidence rather than only appearance.
A phylogenetic explanation should account for both shared features and differences. The fossil record has gaps, so missing intermediate samples do not mean there was no change. Use the full evidence and report how strongly it supports a particular relationship.
Build your understanding
Use three flexible study sessions: core explanation and Parts 1–2; Parts 3–4 with their reasoning checks and models; then the whole-unit application, worked examples, independent practice, and exit check. Allow about 50–60 minutes per session, including diagrams, data work, and notebook explanations. Attempt each check before opening its guidance. Schedule chapter investigations, review, and exams separately; add time where prerequisites are uncertain.
Part 1 · Fossils give a sequence, with gaps
A fossil record consists of preserved remains or traces with geological context. Relative order and numerical age constraints can place observations in time, but preservation and sampling are selective. A transitional combination contains features useful for interpreting relationships, not a claim that every sampled fossil is a direct ancestor. Missing records do not prove nothing happened; a complete inference tests the proposed sequence against several forms of evidence and the geological conditions.
Read the visual model
Identify the labeled structures and units, then trace the arrows or compare values under the caption’s stated conditions. Separate the displayed evidence from a further inference. Write your reasoning before opening the guidance.
Why does no category-C fossil in the oldest sampled bed not prove C existed nowhere at that time?
Visual reasoning — after your attempt
Habitat, preservation, sampling and dating context limit the inference from one record.
In undisturbed sedimentary rock, lower layers were deposited earlier, so the vertical order of fossils provides a relative time sequence. That sequence shows change: groups appear, persist, and disappear, and the assemblages in older layers differ systematically from those in younger ones. Radiometric dating of associated rocks converts relative order into estimated ages.
The record is also incomplete, and saying so is part of using it well. Fossilization requires rapid burial and usually hard parts, so most organisms leave nothing; of those that do, many fossils have been destroyed or remain unexposed. An absence therefore has two possible causes — the group was not there, or it was not preserved or found — so arguments from missing fossils are weak in both directions.
Pause and explain
Why is the absence of fossils for a group during an interval weak evidence that the group did not exist then?
Check your reasoning after answering
Non-preservation and non-discovery produce the same absence as non-existence. Because fossilization is rare and requires particular conditions, most organisms from any interval leave no record, so absence cannot distinguish between those explanations.
Part 2 · Structures: shared plan against shared function
Homologous structures share an ancestral basis, even when their functions differ. Analogous features can serve similar functions through separate evolutionary histories, as in selected flight adaptations. Similarity alone is not enough: compare position, development, detailed structure and molecular evidence. The same broad organ can include homologous underlying parts and independently acquired specializations. Avoid calling every similar-looking outline closely related or every different function unrelated; the explanation depends on the character and level being compared.
Read the visual model
Identify the labeled structures and units, then trace the arrows or compare values under the caption’s stated conditions. Separate the displayed evidence from a further inference. Write your reasoning before opening the guidance.
Does different present-day function rule out homology of an underlying limb plan?
Visual reasoning — after your attempt
No. Descendants can retain an ancestral plan while modifying it for different functions.
Comparative anatomy distinguishes two kinds of similarity. Homologous structures share an underlying plan inherited from a common ancestor even when their functions differ: the forelimbs of a human, a bat, and a whale contain the same bones in the same arrangement, differing in proportion. Analogous structures serve similar functions but differ in plan and ancestry, as a bird's wing and an insect's wing do.
Only homology is evidence of relatedness, which makes the distinction the central skill here. Similarity of appearance or function is not enough, because selection repeatedly produces similar solutions in unrelated lineages — streamlined bodies in dolphins and sharks, for instance. Vestigial structures, reduced and without their ancestral function, are a further case of inherited plan persisting after function changed.
Pause and explain
Why does a dolphin's resemblance to a shark not indicate close relatedness?
Check your reasoning after answering
The resemblance is in outline and function, both shaped by the demands of fast swimming, so it can arise independently. The dolphin's inherited features — mammalian skeleton, lungs, milk — align it with mammals, and inherited plan rather than functional resemblance is what indicates ancestry.
Part 3 · Molecular comparison
An alignment places corresponding sequence positions for comparison. Differences can reflect mutation, shared history and other processes, while different regions evolve under different constraints and rates. A short sequence match alone can arise by chance or be insufficiently informative. Compare suitable homologous sequences, account for uncertainty and test multiple independent regions when possible. Shared derived patterns can support relationships, but a simple difference count does not directly give elapsed time without a calibrated model and assumptions.
Read the visual model
Identify the labeled structures and units, then trace the arrows or compare values under the caption’s stated conditions. Separate the displayed evidence from a further inference. Write your reasoning before opening the guidance.
Could one short matching sequence establish an exact divergence date?
Visual reasoning — after your attempt
No. Dating requires appropriate models, rates/calibration, more evidence and uncertainty, not just a match.
DNA and protein sequences provide a comparison that does not depend on form at all. Species that share a more recent common ancestor have accumulated fewer differences in corresponding sequences, so counting differences estimates relatedness. Because the same genes can be compared across very distantly related organisms, the method reaches relationships that anatomy cannot resolve.
The method's assumptions should be stated. It supposes that differences accumulate at a broadly comparable rate in the lineages compared, that reversals and repeated changes at the same site do not distort the count badly, and that the sequences being compared are genuinely corresponding ones. Where these hold imperfectly, estimates of timing are less reliable than estimates of branching order.
Pause and explain
Species A differs from a reference by 4 amino acids and species B by 12. What is the stronger conclusion, and what is weaker?
Check your reasoning after answering
The stronger conclusion is about order: B's lineage diverged earlier than A's. The weaker one is about timing — that B diverged three times as long ago — because it assumes a comparable rate of change and no repeated or reversed substitutions.
Part 4 · Independent lines that agree
Independent evidence constrains predictions using different observations or methods. A relationship model may explain structural patterns, sequence similarities and temporal context together. Agreement strengthens an explanation when the observations are appropriate and not copies of one source. Disagreement can reveal mistaken homology, incomplete sampling or a model needing revision. Counting supporting examples is not a universal probability or proof score; state how each observation tests a specific predicted relationship and what alternatives remain.
Read the visual model
Identify the labeled structures and units, then trace the arrows or compare values under the caption’s stated conditions. Separate the displayed evidence from a further inference. Write your reasoning before opening the guidance.
Why is three repeated drawings of the same specimen weaker than three different appropriate records?
Visual reasoning — after your attempt
Repeated drawings do not provide independent tests; distinct evidence can constrain different predictions and errors.
Further evidence comes from embryology, where related species show similar early developmental stages; from biogeography, where the distribution of species matches the history of land masses and the isolation of islands; and from directly observed selection in populations with short generations. Each line has its own weaknesses.
The strength of the case lies in their agreement. Fossil sequence, anatomical homology, embryological similarity, molecular comparison, and geographic distribution are affected by different sources of error, so a single alternative explanation would have to account for all of them simultaneously. Convergence of independent methods is the same reasoning pattern that supported endosymbiosis in the cells chapter and the double helix in the genetics chapter.
Pause and explain
Why is agreement between methods with different weaknesses more persuasive than a large amount of evidence of one kind?
Check your reasoning after answering
Evidence of one kind shares one set of possible errors, so a flaw in the method affects all of it. Methods with different weaknesses fail in different ways, so an alternative explanation would have to account for all of them at once, which is far more demanding.
Apply the whole unit · Weigh four kinds of evidence
Illustrative comparisons for four species against a reference mammal. Species P: forelimb with the same bone arrangement, 6 amino-acid differences in a shared protein, fossils of its lineage appear in younger layers. Species Q: streamlined body of similar outline, 71 amino-acid differences, cartilage skeleton, fossils of its lineage appear in much older layers. Species R: forelimb with the same bone arrangement but used for flight, 19 amino-acid differences. Species S: wings of entirely different construction, 94 amino-acid differences.
Your task
Rank the four species by likely closeness of relationship to the reference, name the single most informative piece of evidence for each, identify which similarity in the data is analogous rather than homologous, and explain why the body-outline similarity of species Q is misleading. Then state what additional evidence would most improve the ranking.
What your response should show
- Choose the appropriate biological model or relationship and state the conditions it assumes.
- Show the counts, rates, ratios, or intermediate reasoning the question requires.
- Use the supplied evidence to justify the conclusion and separate observation from inference.
- Identify a meaningful limitation, uncertainty, or next measurement.
Response guidance — after your attempt
Rank by molecular differences: P with 6, R with 19, Q with 71, S with 94 — closest to most distant.
Species P: 6 differences plus the same forelimb bone arrangement, two lines agreeing, so the closest relationship is well supported.
Species R: the same bone arrangement used for a different function is homologous, and 19 differences place it further than P but much closer than Q or S.
Species Q: the streamlined outline is analogous, arising from the demands of swimming, and the cartilage skeleton together with 71 differences places it distant.
Species S: wings of different construction are analogous too, and 94 differences make it the most distant of the four.
Explain the trap in Q: outline is shaped by environment and function and can arise independently, so it is not inherited evidence; the cartilage skeleton and the sequence differences are inherited features and they point the other way.
Improve the ranking: compare several genes rather than one protein, and use dated fossils to calibrate the branching order against time.
The ranking from closest to most distant is P, R, Q, S, following the molecular differences of 6, 19, 71, and 94. For P the evidence is strongest because two independent lines agree: few sequence differences and the same forelimb bone arrangement. R is informative in a different way, since its forelimb has the ancestral bone arrangement adapted to flight — a homologous structure with a changed function, which is evidence of ancestry rather than of current similarity. Q is the instructive case: its streamlined outline resembles the reference, but outline is analogous, produced by the demands of swimming in unrelated lineages, while its cartilage skeleton and 71 sequence differences are inherited features placing it far away. S's wings are likewise analogous. The ranking would be improved by comparing many genes rather than one protein, which reduces the effect of unusual rates at a single locus, and by using dated fossils to calibrate branching order against actual time.
Scientific references and adapted source figures
Parent / teacher teaching notes
The homologous-against-analogous distinction is the whole unit, and the fastest way to test it is to ask what the similarity is in: inherited plan, or current function. Dolphins and sharks make the point in one exchange. Be explicit that each line of evidence has weaknesses and that their agreement is the argument, because that is both the honest account and the reasoning pattern this course keeps returning to. Ask for an explanation of each label, arrow and axis before calculation. Keep first and revised models; attempt the changed case before consulting guidance. Distinguish invented instructional records from named historical sources. Source chromosome symbols are allele-category models, not DNA sequences. These independently authored high-school supplements are not the full OpenSciEd teacher editions or an endorsement.
The key idea
Common ancestry is supported by at least five independent lines of evidence — the fossil record, comparative anatomy (homologous and vestigial structures), embryology, molecular similarity in DNA and proteins, and biogeography — and their agreement, despite using completely different methods, makes the case for evolution extremely strong.
Worked examples
Example 1
- Homologous structures share the same underlying skeletal plan because of common ancestry; analogous structures share only a function.
- The dolphin flipper has the mammalian limb bones (it is homologous with the human arm), but the tuna fin lacks them and is built differently.
- So the dolphin flipper and tuna fin are similar in function only — they are analogous, a product of convergent evolution to swimming.
Example 2 · Worked application
- Similar shapes can result from similar swimming demands.
- Independent anatomical and molecular evidence is needed for relatedness.
- Shared function alone can reflect convergence.
Use multiple characters rather than one superficial similarity.
Example 3
- Principle: the more recently two species share a common ancestor, the more similar their DNA sequences tend to be.
- Higher shared percentage means a more recent common ancestor.
- Order the percentages from highest to lowest: chimp (99%), mouse (85%), chicken (70%), fruit fly (40%).
Example 4
- The corresponding skeletal arrangement is a homologous pattern.
- Inherited modification can produce different functions from a shared structure.
Example 5 · Find and fix the mistake
- Test the claim against the stated conditions: Use multiple characters rather than one superficial similarity.
- Convergence and differing rates of change can mislead appearance-based comparisons.
Use multiple characters rather than one superficial similarity.
Example 6 · Reason from the visual evidence
- An alignment places corresponding sequence positions for comparison. Differences can reflect mutation, shared history and other processes, while different regions evolve under different constraints and rates. A short sequence match alone can arise by chance or be insufficiently informative. Compare suitable homologous sequences, account for uncertainty and test multiple independent regions when possible. Shared derived patterns can support relationships, but a simple difference count does not directly give elapsed time without a calibrated model and assumptions.
- No. Dating requires appropriate models, rates/calibration, more evidence and uncertainty, not just a match.
Original short illustrative sequences, not genomic data from named taxa or a calibrated molecular clock.
Avoid these mistakes
- Similar function alone is not proof of close common ancestry.
Check your understanding
A bat wing and human arm share an underlying bone pattern but differ in function. What inference fits?
Discuss the answer
The pattern supports common ancestry, with other evidence strengthening the relationship.
How can convergent evolution produce similarities without close relationship?
Discuss the answer
Similar pressures can produce analogous functional features through different histories. Appropriate structural, developmental and molecular records help distinguish convergence from close ancestry.
Return to the phenomenon
Return to the initial case. Why can similar function coexist with different ancestry? Revise your drawing or explanation using two named ideas and one stated limitation.
Compare explanations after your attempt
Homology, analogy and convergence concern different histories; multiple independent records are stronger than resemblance alone.
What should we investigate next?
Which comparison would test a remaining uncertainty? State what you would change, keep comparable and measure.
Investigate, explain and revise
Complete these tasks after the teaching parts. Preserve your first model and a supported revision; use guidance after a real attempt.
Activity 1 · Return to the opening case
Use the opening question, defined terms, Parts 1–4 and your notebook. The supplied-data route needs no equipment or external account.
Your task
Return to the initial case. Why can similar function coexist with different ancestry? Revise your drawing or explanation using two named ideas and one stated limitation.
Success criteria
- Use relevant stated observations.
- Explain the mechanism with a labeled model.
- Distinguish quantities and assumptions.
- Describe a revision and a useful next test.
Hint
Follow objects, materials and information separately. Check what each measured quantity means.
Response guidance — discuss after your attempt
Homology, analogy and convergence concern different histories; multiple independent records are stronger than resemblance alone.
Activity 2 · Transfer to a changed case
Cover the worked guidance and use the unit explanations/figures to solve a changed problem.
Your task
Two organisms have similar flight function but different structural/developmental details, while other sequences support separate lineages. Explain how convergence differs from evidence of close ancestry.
Success criteria
- Use the stated measurements or conditions, with correct units.
- Connect the result to the biological mechanism or evidence relationship.
- Identify the assumption, model limit or further evidence requested.
Hint
Name the stated conditions, select the relevant mechanism and show intermediate reasoning.
Response guidance — discuss after your attempt
Similar selection pressures can produce analogous functional resemblance through convergence. Close ancestry requires appropriate shared derived/homologous evidence, supported by independent records; function alone does not settle it.
Words to know
- homologous structures
- Body parts that share the same underlying anatomical plan because they were inherited from a common ancestor, even when they now perform different functions — such as the forelimbs of humans, whales, and bats.
- analogous structures
- Body parts that perform a similar function and may look alike but do not share a recent common origin — such as the wings of insects and birds — resulting from convergent evolution.
- vestigial structure
- A reduced, often nonfunctional structure that is a leftover of a fully functional feature in an ancestor, such as the human appendix or the internal hip bones of a whale.
- transitional fossil
- A fossil that shows a mix of traits from an ancestral group and its descendants, documenting change between forms — such as Tiktaalik, between fish and four-legged animals.
- biogeography
- The study of where species live and how they are distributed across the globe, which reflects their evolutionary history and the movement of the continents.
- molecular evidence
- Similarities in DNA, RNA, and protein sequences among species; the more recently two species shared an ancestor, the more alike their molecules tend to be.
A prediction written in rock: finding Tiktaalik
In the early 2000s, paleontologist Neil Shubin reasoned that the transition from fish to four-legged animals should have happened in rocks about 375 million years old, so his team searched Devonian-age rock in the Canadian Arctic. In 2004 they found Tiktaalik, a creature with fish scales and gills but also a mobile neck, sturdy wrist-like bones, and lungs. The power of the discovery wasn't just the fossil — it was that evolutionary theory predicted the age and type of rock to dig in before anyone found it.
From land to sea: tracing whale ancestry
Few fossil sequences are as complete as the whales'. A chain of fossils — from the four-legged, deer-sized Pakicetus, to the crocodile-like Ambulocetus ('walking whale'), to species with ever-smaller hind limbs — documents mammals returning to the ocean over roughly ten million years. Modern whales still carry tiny, internal hip and leg bones, vestigial echoes of those walking ancestors, and their DNA confirms they are most closely related to hippos among living animals.
The same code in every cell
A gene taken from a firefly can be inserted into a tobacco plant and make it glow, and a human gene can be read correctly by bacteria — because virtually every organism on Earth uses the same genetic code, the same rules for translating DNA into proteins. If life had arisen many separate times, we would expect many different codes. Instead, the near-universal code is exactly what we'd predict if all life shares a single common ancestor, making it some of the deepest molecular evidence for evolution.
Shared typos: what broken genes reveal
Most mammals make their own vitamin C, but humans, chimpanzees, and other apes cannot — we all carry the same broken version of the GULO gene, disabled by the same genetic 'typo.' A shared functional gene could be a coincidence, but sharing the identical mistake is powerful evidence of inheritance from a common ancestor, just as two students with the exact same unusual error on a test suggest a shared source. Our genomes are full of such shared pseudogenes and viral insertions sitting at identical positions across related species.
Why kangaroos live in Australia
Australia is overrun with marsupials — kangaroos, koalas, wombats — and has almost no native placental mammals, while the rest of the world shows the reverse. Biogeography explains why: Australia broke away and drifted in isolation for tens of millions of years, so its early marsupials diversified there without competition from placental mammals. The naturalist Alfred Russel Wallace even mapped a sharp boundary, now called the Wallace Line, where Asian and Australian animal groups abruptly change — a border drawn not by today's geography but by deep evolutionary history.
In the real world
Because all life shares the same genetic code and deeply similar molecules, researchers can insert a human gene into bacteria and have those bacteria mass-produce human insulin for people with diabetes — a life-saving payoff of the shared evolutionary chemistry that molecular evidence reveals.
Exit check
Why is agreement between molecular and anatomical evidence useful for common ancestry?
Check your explanation after answering
Independent evidence constrains alternative explanations and supports a consistent branching model; any one feature can be ambiguous or convergent.
Explain your reasoning without notes. If a key idea is missing, revisit the lesson and try again.
Problem 1
- a total absence of any evolutionary relationship
- descent from a common ancestor
- convergent evolution from unrelated ancestors
- traits acquired during life
Answer and explanation
descent from a common ancestor
Homologous structures share an underlying anatomical plan because the species inherited it from a common ancestor, even though the structures now serve different functions.
Problem 2
- Humans and chimpanzees share about 98-99% of their DNA sequence
- A bat wing and a bird wing both allow flight
- Fossils in deeper rock layers are older
- Kangaroos are found mainly in Australia
Answer and explanation
Humans and chimpanzees share about 98-99% of their DNA sequence
Molecular evidence compares DNA, RNA, or protein sequences. High DNA similarity indicates a recent common ancestor. The other choices are anatomical, fossil, and biogeographic evidence.
Problem 3
Answer and explanation
Homologous structures share the same underlying anatomical plan because of a common ancestor, even if they now have different functions (like a human arm and a bat wing). Analogous structures share only a function and are built differently (like a bird wing and an insect wing), arising from convergent evolution. Only homologous structures are evidence of common ancestry.
Problem 4
- Vestigial structures
- Comparative embryology
- Biogeography — Australia's long isolation let its mammals diverge separately from those on other continents
- The universal genetic code
Answer and explanation
Biogeography — Australia's long isolation let its mammals diverge separately from those on other continents
Biogeography examines how species are distributed. Australia's tens of millions of years of isolation allowed its marsupials to diversify separately, which is why they are found there and almost nowhere else.
Problem 5
Answer and explanation
40 million years
8 differences x 5 million years per difference = 40 million years.
Problem 6
Answer and explanation
The pattern supports common ancestry, with other evidence strengthening the relationship.
The corresponding skeletal arrangement is a homologous pattern.
Inherited modification can produce different functions from a shared structure.
Response criteria
- Use the stated conditions.
- Show the evidence or calculation.
- Explain the conclusion and any stated limitation.
Problem 7
Hints
Use multiple characters rather than one superficial similarity.
Answer and explanation
Inheritance explains nested shared features; compare many positions and alternative explanations.
Problem 8
Hints
State what the supplied observations or conditions establish, and separate that from any assumption.
Answer and explanation
No. Preservation and sampling are incomplete; evaluate all available evidence and the model's predictions.
Problem 9
Answer and explanation
No. Dating requires appropriate models, rates/calibration, more evidence and uncertainty, not just a match.
An alignment places corresponding sequence positions for comparison. Differences can reflect mutation, shared history and other processes, while different regions evolve under different constraints and rates. A short sequence match alone can arise by chance or be insufficiently informative. Compare suitable homologous sequences, account for uncertainty and test multiple independent regions when possible. Shared derived patterns can support relationships, but a simple difference count does not directly give elapsed time without a calibrated model and assumptions.
No. Dating requires appropriate models, rates/calibration, more evidence and uncertainty, not just a match.
Response criteria
- Read the structures, axes, directions and units correctly.
- Connect the evidence with the biological mechanism.
- Respect stated model assumptions and distinguish an observation from a further inference.
Problem 10
Answer and explanation
Similar selection pressures can produce analogous functional resemblance through convergence. Close ancestry requires appropriate shared derived/homologous evidence, supported by independent records; function alone does not settle it.
Similar selection pressures can produce analogous functional resemblance through convergence. Close ancestry requires appropriate shared derived/homologous evidence, supported by independent records; function alone does not settle it.
Response criteria
- Use the stated measurements or conditions, with correct units.
- Connect the result to the biological mechanism or evidence relationship.
- Identify the assumption, model limit or further evidence requested.