Passage Summary: Only primates have thumbs that can move against their fingers. Lemurs are the only primates in Madagascar, and some of them are the only lower primates active during the day. All higher primates come from one type of daytime-active lower primate.

Reasoning: Only primates have opposable thumbs; lemurs are the only primates in Madagascar; some lemurs are the only diurnal lower primates; and higher primates evolved from a diurnal lower primate species.

Analysis: This set of facts allows for several transitive deductions. Because only primates have opposable thumbs and lemurs are primates, it must be true that any lemur has opposable thumbs. Furthermore, since lemurs are the only primates in Madagascar, any animal in Madagascar with an opposable thumb must be a lemur. The information about diurnal lower primates also suggests a specific evolutionary branch, though the most airtight inferences will likely involve the unique physical trait of the opposable thumb. Focus on combining the 'only' statements to find a necessary overlap.