# When evolution runs backwards: answers and explanations

Cambridge IELTS 10, Test 4, Reading Passage 3

Source: Passage, questions and answer key from Cambridge IELTS 10, Test 4, Reading Passage 3. © Cambridge University Press & Assessment. Used for educational practice. Explanations and evidence notes are written by Testmigo.

## Answer key

| Q | Answer | Proof |
| --- | --- | --- |
| 27 | C | Early 20th-century biologists came to a similar conclusion, though they qualified it in terms of probability |
| 28 | D | Explorer Roy Chapman Andrews argued at the time that the whale must be a throwback to a land-living ancestor. |
| 29 | C | If these silent genes are somehow switched back on, they argued, long-lost traits could reappear. |
| 30 | B | The salamander example fits with Raff's 10-million-year time frame. |
| 31 | A | digit loss and gain has occurred on more than one occasion over tens of millions of years. |
| 32 | F | most biologists have been reluctant to use those words, mindful of a principle of evolution that says 'evolution cannot run backwards' |
| 33 | G | While Lombroso was measuring criminals, a Belgian palaeontologist called Louis Dollo was studying fossil records and coming to the opposite conclusion. |
| 34 | A | And this poses a puzzle: how can characteristics that disappeared millions of years ago suddenly reappear? |
| 35 | B | similar structures can independently arise in unrelated species, such as the dorsal fins of sharks and killer whales. |
| 36 | D | the genetic information needed to make toes somehow survived for tens or perhaps hundreds of millions of years in the lizards and was reactivated. |
| 37 | NOT GIVEN | biologist Gunter Wagner of Yale University reported some work on the evolutionary history of a group of South American lizards called Bachia. |
| 38 | YES | the toed species re-evolved toes from toeless ancestors |
| 39 | NO | Early embryos of many species develop ancestral features. |
| 40 | YES | 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. |

## Why these answers are right

**27. C.** You need what the writer says about Louis Dollo's theory. Paragraph C explains that early 20th-century biologists reached a similar view but "qualified it in terms of probability," saying reversal was unlikely rather than impossible. Qualifying a theory means modifying it, so C is right.

**28. D.** The question asks why the Vancouver Island humpback whale is mentioned. Paragraph D focuses on its leg-like appendages and on Roy Chapman Andrews's explanation that it must be a throwback to a land-living ancestor. That is the reason given for its unusual features, option D.

**29. C.** This asks what the passage says about silent genes. Paragraph E reports Raff's argument that if these switched-off genes are "switched back on," long-lost traits could reappear. Traits reappearing is the re-emergence of certain characteristics, so the answer is C.

The why and the trap for questions 30 onwards are free with an account on the [answers page](https://testmigo.com/ielts/reading/when-evolution-runs-backwards/answers).

[Practice When evolution runs backwards](https://testmigo.com/ielts/reading/when-evolution-runs-backwards)