Question 4·Easy·Inferences
On a small island, biologists tracked a population of lizards for twenty years. During unusually dry years, the insects that lizards eat became scarce. The researchers observed that lizards with longer legs could travel farther in search of food and were more likely to survive and reproduce in those dry years. In wet years, when insects were plentiful, leg length did not affect survival rates. By the end of the study, the average leg length of the island lizard population had increased slightly.
Taken together, these observations most strongly support which inference?
For inference questions in Reading & Writing, first restate in your own words what the passage shows—especially causes, effects, and patterns over time—before looking at the choices. Then, choose the option that best explains or extends that pattern without adding new, unsupported details or extreme language. For science-style passages like this, look for how a trait affects survival and reproduction, and how that could change the population over many years; answers that match this logic of cause → survival/reproduction → population change are usually stronger than ones that just restate a single fact or introduce new ideas.
Hints
Focus on all parts of the description
Reread the details about dry years, wet years, and the change in average leg length after twenty years. Ask yourself: what long-term pattern do these details describe?
Think about advantage and reproduction
Which lizards are more likely to survive and reproduce in the dry years? How would that affect the traits of the overall population after many generations?
Use the change over time
The last sentence says the average leg length increased slightly. Which answer choice actually explains this gradual change, rather than just mentioning precipitation or a single type of year?
Eliminate choices that add new ideas
Cross out any answer that talks about things the passage never mentions, like lizards leaving the island or muscles being weakened, or that uses extreme words like “solely” that the passage doesn’t support.
Step-by-step Explanation
Identify what the question is asking
The question asks: “Taken together, these observations most strongly support which inference?” That means you need to combine all the details given (dry years, wet years, survival, reproduction, and change over time) and choose the statement that best explains what is happening, not just restate one sentence.
Summarize the key observations
From the passage:
- In dry years, insects are scarce.
- In those dry years, lizards with longer legs can travel farther, are more likely to survive, and are more likely to reproduce.
- In wet years, insects are plentiful, and leg length does not affect survival.
- After twenty years, the average leg length increased slightly in the population.
So, a certain trait (longer legs) gives an advantage only in certain conditions (dry years), and after many years that trait becomes more common in the population.
Connect the pattern to the underlying concept
When a trait helps some individuals survive and reproduce more than others, those individuals are more likely to pass that trait to their offspring. Over many generations, that helpful trait becomes more common in the population, which shows up as a change in the average value of the trait (here, leg length). This process is called natural selection: the environment favors certain inherited traits, so they spread over time.
Match the reasoning to the answer choices
Now compare each option to this idea:
- The correct inference must explain why longer-legged lizards did better in dry years and why the average leg length increased over time.
- It should not introduce new claims (like lizards leaving the island or muscles weakening) that the passage never mentions.
Choice B) Natural selection favored longer-legged lizards during dry years, leading to an increase in average leg length over time. exactly matches the observations: longer legs gave a survival/reproduction advantage in dry years, so over many years the population’s average leg length increased. This is the best-supported inference.