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, track how a trait affects survival and reproduction and how that could change the population over many years.
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 must combine all the details given (dry years, wet years, survival, reproduction, and change over time) and choose the statement that best explains the overall pattern, not just one detail.
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, longer legs help in dry years, and over time the population shifts slightly toward longer legs.
Connect advantage to population change over time
If longer-legged lizards survive and reproduce more during dry years, they will tend to have more offspring. Over many years (many generations), that advantage can make longer legs more common in the population, which would raise the average leg length.
Match the reasoning to the answer choices
The inference that fits the evidence must link (1) the dry-year advantage for longer legs to (2) survival and reproduction and (3) a gradual increase in average leg length over time.
Therefore, the best choice is: Dry years gave longer-legged lizards a survival and reproduction advantage, so longer legs became slightly more common over time.