SAT Critical Reading : Understanding the Content of Natural Science Passages
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Example Question #11 : Main Idea, Details, Opinions, And Arguments In Narrative Science Passages
Adapted from "Taking a Second Look: An Analysis of Genetic Markers in Species Relatedness" by Joseph Ritchie (2014)
Phylogenetics is the study of genetic composition in various species and is used by evolutionary biologists to investigate similarities in the molecular sequences of proteins in varying organisms. The amino acid sequences that build proteins are used to construct mathmatical matrices that aid in determining evolutionary ties through the investigation of percentage similarities. The study of these matrices helps to expose evolutionary relationships between species that may not have the same overt characteristics.
Species adapt and evolve based on the pressures that exist in their environment. Climate, food source, and habitat availability are only a few factors that act on species adaptation. These stressors can alter the physical characteristics of organisms. This divergence in evolution has made it difficult to determine the interrelatedness of organisms by analyzing their physical characteristics alone.
For instance, looking only at physical characteristics, the ghost bat resembles a pigeon more than a spider monkey; however, phylogenetics has found that the amino acid sequences that construct the beta hemoglobin molecules of bats are twenty percent more similar to those of mammalian primates than those of birds. This helps reject the assumption that common physical characteristics between species are all that is needed to determine relatedness.
The differences produced by divergent evolution observed in the forest-dwelling, arboreal spider monkey and the nocturnal, airborne ghost bat can be reconciled through homology. Homologous characteristics are anatomical traits that are similar in two or more different species. For instance, the bone structure of a spider monkey’s wrist and fingers greatly resembles that of a bat’s wing or even a whale’s fin. These similarities are reinforced by phylogenetic evidence that supports the idea that physically dissimilar species can be evolutionarily related through anatomical and genetic similarities.
The central idea of this passage is best described by which of the following statements?
Despite differences in physical appearance, genetic similarities can aid in determining species relatedness and evolutionary histories.
Genetic analysis is the only method of studying evolutionary ties and species relatedness.
Understanding divergent evolution is necessary for understanding species relatedness.
Phylogenetics is a relatively new area of study and has yet to yield supported conclusions on evolutionary histories.
Despite differences in physical appearance, genetic similarities can aid in determining species relatedness and evolutionary histories.
This is the correct answer because it is the only statement that is supported by the passage. The passage introduces the field of phylogenetics and the need to explore evolution beyond simple examination of physical characteristics. It does not state which field of study is better or correct. It simply states that they compliment the same cause: the study of relatedness. The other choices are unsupported opinions. The answer choice about divergent evolution is incorrect because while the passage's fourth paragraph is about divergent evolution, the entire passage encompasses many more topics.
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