When Evolution Runs Backwards — IELTS Reading Answers

When discussing the theory developed by Louis Dollo, the writer says that

1. Ait was immediately referred to as Dollo’s law.
2. Bit supported the possibility of evolutionary throwbacks.
3. Cit was modified by biologists in the early twentieth century.correct
4. Dit was based on many years of research.

“Early 20th-century biologists came to a similar conclusion, though they qualified it in terms of probability, stating that there is no reason why evolution cannot run backwards – it is just very unlikely.”

Later biologists kept Dollo's conclusion but qualified it in terms of probability, which is a modification by early twentieth-century biologists, option C.

The humpback whale caught off Vancouver Island is mentioned because of

1. Athe exceptional size of its body.
2. Bthe way it exemplifies Dollo’s law.
3. Cthe amount of local controversy it caused.
4. Dthe reason given for its unusual features.correct

“Explorer Roy Chapman Andrews argued at the time that the whale must be a throwback to a land-living ancestor.”

The whale is cited because Andrews explained its features as a throwback to a land-living ancestor, which is option D, the reason given for them.

What is said about ‘silent genes’?

1. ATheir numbers vary according to species.
2. BRaff disagreed with the use of the term.
3. CThey could lead to the re-emergence of certain characteristics.correct
4. DThey can have an unlimited life span.

“If these silent genes are somehow switched back on, they argued, long-lost traits could reappear.”

Switching silent genes back on would let long-lost traits reappear, matching option C's re-emergence of certain characteristics.

The writer mentions the mole salamander because

1. Ait exemplifies what happens in the development of most amphibians.
2. Bit suggests that Raff’s theory is correct.correct
3. Cit has lost and regained more than one ability.
4. Dits ancestors have become the subject of extensive research.

“As a possible example, the team pointed to the mole salamanders of Mexico and California.”

The team pointed to the mole salamanders as a possible example, so the creature supports Raff's theory, which is option B.

Which of the following does Wagner claim?

1. AMembers of the Bachia lizard family have lost and regained certain features several times.correct
2. BEvidence shows that the evolution of the Bachia lizard is due to the environment.
3. CHis research into South American lizards supports Raff’s assertions.
4. DHis findings will apply to other species of South American lizards.

“According to his analysis of the Bachia family tree, 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.”

Wagner finds digit loss and gain occurred on more than one occasion over tens of millions of years, so features were lost and regained repeatedly, option A.

For a long time biologists rejected

“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.”

For the better part of a century biologists avoided those words, holding that evolution cannot run backwards, which is ending F.

Opposing views on evolutionary throwbacks are represented by

“While Lombroso was measuring criminals, a Belgian palaeontologist called Louis Dollo was studying fossil records and coming to the opposite conclusion.”

Dollo reached the opposite conclusion to Lombroso, so the pair represents the opposing views on throwbacks, ending G.

Examples of evolutionary throwbacks have led to

“Since then, so many other examples have been discovered that it no longer makes sense to say that evolution is as good as irreversible. And this poses a puzzle: how can characteristics that disappeared millions of years ago suddenly reappear?”

So many examples were discovered that calling evolution irreversible no longer made sense, and this poses a puzzle, which is ending A.

The shark and killer whale are mentioned to exemplify

“in much the same way that similar structures can independently arise in unrelated species, such as the dorsal fins of sharks and killer whales.”

The dorsal fins of sharks and killer whales show similar structures arising independently in unrelated species, illustrating convergent evolution, ending B.

One explanation for the findings of Wagner’s research is

“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.”

One explanation is that the genetic information needed to make toes survived for millions of years and was reactivated, ending D.

Wagner was the first person to do research on South American lizards.

“In a paper published last year, biologist Gunter Wagner of Yale University reported some work on the evolutionary history of a group of South American lizards called Bachia.”

The text introduces Wagner's paper on Bachia lizards but never says whether anyone researched South American lizards before him.

Wagner believes that Bachia lizards with toes had toeless ancestors.

“According to his analysis of the Bachia family tree, the toed species re-evolved toes from toeless ancestors”

Wagner's analysis says the toed species re-evolved toes from toeless ancestors, exactly the belief stated in the question.

The temporary occurrence of long-lost traits in embryos is rare.

“Early embryos of many species develop ancestral features.”

Ancestral features appear in the early embryos of many species, making the phenomenon common rather than rare, so the statement is contradicted.

Evolutionary throwbacks might be caused by developmental problems in the womb.

“If for any reason this does not happen, the ancestral feature may not disappear, leading to an atavism.”

When normal development fails, the ancestral feature may not disappear, leading to an atavism, linking throwbacks to disrupted development before birth.