Text 1
For decades, researchers debated the function of the narwhal’s () elongated tusk. In a 2014 study, Martin Nweeia and colleagues proposed that the tusk serves as a sensory organ. By analyzing the tusk’s structure, they discovered millions of nerve endings connecting the outer environment to the narwhal's brain. Nweeia's team demonstrated that exposing the tusk to varying salinity levels triggered immediate changes in the whale’s heart rate, suggesting that narwhals use their tusks to detect oceanographic variations and navigate through Arctic ice.
Text 2
While the sensory hypothesis is intriguing, evolutionary biologist Zackary Graham argues that the narwhal tusk is primarily a product of sexual selection. Graham’s team analyzed physical measurements of hundreds of narwhals, finding that tusk length is highly variable among males of the same age, a trait characteristic of ornaments used to signal social status or attract mates. Furthermore, because females rarely grow tusks and survive without the sensory input they supposedly provide, Graham contends that the tusk’s primary function is as a visual signal in male-male competition, rather than a critical survival tool.
Based on the texts, how would Graham (Text 2) most likely characterize the finding in Text 1 that narwhals exhibit changes in heart rate when their tusks are exposed to different salinity levels?
- As a physiological response that, while genuine, does not demonstrate that the tusk is necessary for survival, since female narwhals navigate successfully without one.Answer
- BAs a flawed finding that mistakenly attributes cardiovascular changes to salinity rather than to the stress of male-male competition.
- CAs evidence that helps explain why male narwhals exhibit more erratic heart rates than female narwhals during seasonal migrations.
- DAs support for his own theory that male narwhals use changes in ocean salinity to locate potential mates in icy waters.