When evolution runs backwards: reading answers and analysis
Biologists long held, following Dollo, that evolution can't run backwards, but examples of 'throwbacks' keep appearing. Raff suggested silent genes could revive lost traits within about 10 million years. Wagner's toed lizards break that limit, so the writer turns to embryos, which often show ancestral features before development removes them.
The multiple choice (27-31) follows the examples in order, from Dollo to Wagner. The sentence endings (32-36) jump between paragraphs 1, 2-3, 5 and 9. YES / NO / NOT GIVEN (37-40) is in paragraph 8 and the last paragraph.
Answer key and self-check
Type what you wrote and hit mark. Hide the key first if you haven't done the passage yet. Every question number jumps to its explanation.
How to attack this block: Each question asks why an example is there, so find the sentence where the writer comments on it. Dollo's idea was qualified, the whale matters for the explanation of its legs, the salamander fits Raff's timescale, and Wagner's lizards lost and regained toes repeatedly.
Question 27
Answer: CParagraph 3, second half
What does the writer say about Louis Dollo's theory?
Early 20th-century biologists came to a similar conclusion, though they qualified it in terms of probability
Question says → Passage says
biologists in the early twentieth centuryEarly 20th-century biologists
modifiedqualified it in terms of probability
Why: To 'qualify' a claim is to limit or adjust it. Early 20th-century biologists changed Dollo's 'impossible' into 'very unlikely', so the theory was modified: C.
The trap: A tempts because the name 'Dollo's law' is mentioned, but the passage says the idea 'stuck and came to be known as' that, which suggests over time, not immediately. B is the opposite of his view.
Question 28
Answer: DParagraph 4, second half
Why is the humpback whale caught off Vancouver Island mentioned?
Explorer Roy Chapman Andrews argued at the time that the whale must be a throwback to a land-living ancestor.
Question says → Passage says
the reason givenargued at the time that
its unusual featuresa pair of leg-like appendages over a metre long
Why: The whale had legs, and Andrews explained them as a throwback to a land ancestor. The passage cares about that explanation, because it's an exception to Dollo's law: D.
The trap: A picks up 'over a metre long', but that's the size of the leg-like parts, not the whale's body. B is the reverse: the whale is an exception to Dollo's law, not an example of it.
Question 29
Answer: CParagraph 5, last sentence
What does the passage say about 'silent genes'?
If these silent genes are somehow switched back on, they argued, long-lost traits could reappear.
Question says → Passage says
could lead toIf… switched back on… could reappear
the re-emergence of certain characteristicslong-lost traits could reappear
Why: Switched-off genes might be switched back on and bring old traits back. 'Re-emergence of characteristics' is 'traits reappearing': C.
The trap: D is contradicted in the next paragraph: silent genes collect mutations and survive about 6 to 10 million years at most. A and B aren't mentioned.
Question 30
Answer: BParagraph 7, last sentence
Why does the writer mention the mole salamander?
In other words, metamorphosis in mole salamanders is an atavism. The salamander example fits with Raff's 10-million-year time frame.
Question says → Passage says
suggests that Raff's theory is correctfits with Raff's 10-million-year time frame
Why: Raff's team itself pointed to the salamanders 'as a possible example', and the writer ends by saying it fits Raff's time limit. That supports Raff's theory: B.
The trap: C describes the Bachia lizards in the next paragraph, which lost and regained toes more than once. A is wrong because the axolotl is the exception to normal amphibian development.
Question 31
Answer: AParagraph 8, last sentence
What does Wagner claim?
the toed species re-evolved toes from toeless ancestors and, what is more, digit loss and gain has occurred on more than one occasion over tens of millions of years
Question says → Passage says
lost and regaineddigit loss and gain
certain featurestoes / digit
several timeson more than one occasion
Why: Wagner says toes were lost and regained more than once in the Bachia family. Toes are 'certain features', and 'on more than one occasion' is 'several times': A.
The trap: C is the opposite: the paragraph opens by saying these examples 'break the time limit', so they challenge Raff rather than support him. B and D are never mentioned.
Sentence endings (A-G)
Questions 32-36
How to attack this block: Several endings sound alike, so match the exact relationship. What biologists rejected is reversibility. The puzzle the examples raise is how lost traits return. Sharks and killer whales show one feature in unrelated species, and the second explanation for Wagner is genetic information surviving.
Question 32
Answer: FParagraph 1, second sentence
What did biologists reject for a long time?
For the better part of a century, most biologists have been reluctant to use those words, mindful of a principle of evolution that says 'evolution cannot run backwards'.
Question says → Passage says
for a long timeFor the better part of a century
rejectedhave been reluctant to use those words
the possibility of evolution being reversibleevolution cannot run backwards
Why: Biologists avoided the term because they believed evolution can't go backwards. In other words, they rejected the idea that it's reversible: F.
The trap: E (doubts about throwbacks) reads like the same topic, but biologists held those doubts. They didn't reject them.
Question 33
Answer: GParagraphs 2 and 3
Who represents the opposing views on evolutionary throwbacks?
While Lombroso was measuring criminals, a Belgian palaeontologist called Louis Dollo was studying fossil records and coming to the opposite conclusion.
Question says → Passage says
opposing viewscoming to the opposite conclusion
Dollo's findings and the convictions held by LombrosoLombroso… Louis Dollo
Why: Lombroso believed criminals were throwbacks; Dollo concluded that evolution can't reverse. The passage itself calls Dollo's view 'the opposite conclusion': G.
The trap: C (behaviour and appearance) picks up Lombroso's idea of identifying criminals by physical features. That's one detail of one side, not the two opposing views.
Question 34
Answer: AParagraph 5, first two sentences
What have examples of evolutionary throwbacks led to?
And this poses a puzzle: how can characteristics that disappeared millions of years ago suddenly reappear?
Question says → Passage says
have led tothis poses
the question of howa puzzle: how can
certain long-lost traits could reappearcharacteristics that disappeared millions of years ago suddenly reappear
Why: So many examples have been found that evolution can't be called irreversible, and that raises a puzzle: how can lost traits come back? A puzzle is a question: A.
The trap: F (the possibility of evolution being reversible) also follows from the examples, but F is already the answer to question 32. The ending that matches 'poses a puzzle' word for word is A.
Question 35
Answer: BParagraph 9, second sentence
What are the shark and the killer whale examples of?
in much the same way that similar structures can independently arise in unrelated species, such as the dorsal fins of sharks and killer whales
Question says → Passage says
a particular featuresimilar structures / the dorsal fins
in different speciesin unrelated species
Why: Sharks and killer whales aren't related, yet both have dorsal fins. They show the same feature appearing in different species: B.
The trap: D (genetic information surviving) is the other explanation in the same paragraph, and it fits question 36, not the sharks.
Question 36
Answer: DParagraph 9, third sentence
What is one explanation for Wagner's findings?
Another more intriguing possibility is that the genetic information needed to make toes somehow survived for tens or perhaps hundreds of millions of years in the lizards and was reactivated.
Question says → Passage says
one explanationAnother more intriguing possibility
the continued existence of certain genetic informationthe genetic information needed to make toes somehow survived
Why: The lizards' toes could have come back because the genetic information for making toes survived and was switched on again. 'Survived' is 'continued existence': D.
The trap: B also explains how features reappear, but it's the shark example of independent evolution. The ending about information surviving is D.
YES / NO / NOT GIVEN
Questions 37-40
How to attack this block: Read Wagner's own view carefully, because the paragraph first gives the simple explanation he rejects. The NO turns on 'many species', which makes ancestral features in embryos common, not rare.
Question 37
Answer: NOT GIVENParagraph 8, second sentence
Was Wagner the first to research South American lizards?
biologist Gunter Wagner of Yale University reported some work on the evolutionary history of a group of South American lizards called Bachia
Question says → Passage says
research on South American lizardsreported some work on the evolutionary history of a group of South American lizards
Why: The passage says Wagner published work on these lizards, but not whether anyone studied them before him. NOT GIVEN.
The trap: 'More recently' at the start of the paragraph can feel like 'new' research. It means recent, not first.
Question 38
Answer: YESParagraph 8, last two sentences
Does Wagner think the Bachia lizards with toes came from toeless ancestors?
According to his analysis of the Bachia family tree, the toed species re-evolved toes from toeless ancestors
Question says → Passage says
Wagner believesWagner begs to differ. According to his analysis
lizards with toes had toeless ancestorsthe toed species re-evolved toes from toeless ancestors
Why: Wagner's analysis says the toed species grew toes again from ancestors without them. That matches the statement directly: YES.
The trap: 'The simplest explanation is that the toed lineages never lost their toes' is the view Wagner rejects. Don't confuse that with his own belief.
Question 39
Answer: NOLast paragraph, third and fourth sentences
Is it rare for embryos to show long-lost traits for a while?
Early embryos of many species develop ancestral features. Snake embryos, for example, sprout hind limb buds.
Question says → Passage says
long-lost traitsancestral features
temporary occurrenceLater in development these features disappear
raremany species
Why: The writer says embryos of many species develop ancestral features that later disappear. 'Many species' means it's common, which contradicts 'rare': NO.
The trap: The atavism that stays (when the feature doesn't disappear) is the unusual case. The temporary appearance in embryos is what's common.
Question 40
Answer: YESLast paragraph, last two sentences
Could throwbacks be caused by something going wrong in development in the womb?
The answer may lie in the womb… If for any reason this does not happen, the ancestral feature may not disappear, leading to an atavism.
Question says → Passage says
might be caused bymay lie in / leading to
developmental problemsIf for any reason this does not happen
evolutionary throwbacksan atavism
Why: Normally a developmental program removes the ancestral feature. If it fails, the feature stays and you get an atavism. A failed program is a developmental problem, and 'may' matches 'might': YES.
C. Early 20th-century biologists 'qualified' Dollo's idea, turning impossible into very unlikely. The name 'Dollo's law' came later.
Words from this passage worth keeping
throwback(Paragraph 1)
a living thing showing features of a much earlier ancestor
connotations(Paragraph 2)
ideas or feelings a word suggests beyond its meaning
irreversible(Paragraph 3)
impossible to change back
qualified(Paragraph 3)
limited or modified a statement
appendages(Paragraph 4)
parts such as limbs that stick out from the body
lineage(Paragraph 7)
a line of descent from an ancestor
minuscule(Paragraph 8)
extremely small
degrade(Last paragraph)
break down and get worse over time
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The full Cambridge 10 Test 4 reading paper: all three passages, 60 minutes, marked the second you finish with a review of every answer. Already done it? Take it again and see if the same traps still get you.
Cambridge IELTS 10, Test 4, Reading Passage 3. The passage and questions belong to Cambridge University Press and are not reproduced here. We quote short extracts only as evidence for our own commentary, and the answers are published for self-marking. Get the book for the full text, or sit the test on Langujet.
