Highlight Correct Summary – This is an item type that integrates listening and reading skills, and requires test takers to understand, analyze and combine information from a recording, and then identify the most accurate summary of the recording.
Listen to the following audio and choose most accurate summary of the recording.
[A]. Artificially synthesized chemicals might eventually serve to alter the course of evolution by desensitizing humans to certain tastes and odors.
[B]. Some human polymorphisms might be explained as vestigial evidence of evolutionary adaptations that still serve vital purposes in other primates.
[C]. Sensitivity to taste and to odors have been subject to far greater natural selectivity during the evolution of primates than previously thought.
[D]. Polymorphism among human populations varies considerably from region to region throughout the world.
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TRANSCRIPT (Only for reference, it will not be given in actual PTE Academic Test)
In nearly all human populations a majority of individuals can taste the artificially synthesized chemical Phenylthiocarbamide (PTC). However, the percentage varies dramatically–from as low as 60% in India to as high as 95% in Africa. Click here to read full transcript
That this polymorphism is observed in non-human primates as well indicates a long evolutionary history which, although obviously not acting on PTC, might reflect evolutionary selection for taste discrimination of other, more significant bitter substances, such as certain toxic plants.
A somewhat more puzzling human polymorphism is the genetic variability in earwax, or cerumen, which is observed in two varieties. Among European populations 90% of individuals have a sticky yellow variety rather than a dry, gray one, whereas in northern China these numbers are approximately the reverse. Perhaps like PTC variability, cerumen variability is an incidental expression of something more adaptively significant. Indeed, the observed relationship between cerumen and odorous bodily secretions, to which non-human primates and, to a lesser extent humans, pay attention suggests that during the course of human evolution genes affecting body secretions, including cerumen, came under selective influence.