In Nearly All Human Populations, A Majority of Individuals can Taste the Artificially Synthesized Chemical Phenylthiocarbonide (PTC).

Reading Passage Question

In nearly all human populations, a majority of individuals can taste the artificially synthesized chemical phenylthiocarbonide (PTC). However, the percentage varies dramatically—from as low as 60 percent in India to as high as 95 percent in Africa. That this polymorphism is observed in nonhuman 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 percent 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 nonhuman 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.

“In nearly all human populations, a majority of individuals can taste the artificially synthesized chemical phenylthiocarbonide (PTC)” - this is a GMAT reading comprehension passage with answers. Candidates need a strong knowledge of English GMAT reading comprehension.

This GMAT Reading Comprehension consists of 3 comprehension questions. The GMAT Reading Comprehension questions are designed for testing candidates’ abilities in understanding, analyzing, and applying information or concepts. Candidates can actively prepare with the help of GMAT Reading Comprehension Practice Questions.

Solution and Explanation

1. It can be inferred from the passage that human populations vary considerably in their

(A) sensitivity to certain bodily odors.
(B) capacity for hearing.
(C) ability to assimilate artificial chemicals.
(D) vulnerability to certain toxins found in plants.
(E) ability to discern bitterness in taste.

2. Which of the following provides the most reasonable explanation for the assertion in the first paragraph that evolutionary history “obviously” did not act on PTC?

(A) PTC is not a naturally occurring chemical but rather has been produced only recently by scientists.
(B) Most humans lack sufficient taste sensitivity to discriminate between PTC and bitter chemicals occurring naturally.
(C) Variability among humans respecting PTC discrimination, like variability respecting earwax, cannot be explained in terms of evolutionary adaptivity.
(D) The sense of taste in humans is not as discriminating as that in nonhuman primates.
(E) Unlike nonhuman primates, humans can discriminate intellectually between toxic and nontoxic bitter substances.

3. Which of the following best expresses the main idea of the passage?

(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.
(E) The human senses of taste and smell have evolved considerably over the course of evolutionary history.

Suggested GMAT Reading Comprehension Samples

• A One-Child Policy was Implemented in China in 1979
• The Pioneers of the Teaching of Science Imagined that its Introduction into Education would Remove the Conventionality, Artificiality, and Backward-Lookingness
• A Fundamental Principle of Pharmacology is that all Drugs have Multiple Actions. Actions that are Desirable in the Treatment of Disease are Considered therapeutic
• In the 1980's, Astronomer Bohdan Paczynski Proposed a Way of Determining Whether the Enormous Dark Halo Constituting the Outermost Part of the Milky Way Galaxy
• The General Density Dependence Model can be Applied to Explain the Founding of Specialist Firms
• Many People Believe that Wages are Lower in Developing Countries than in Developed Countries
• More Selective than Most Chemical Pesticides in that they Ordinarily Destroy only Unwanted Species
• Citing the Fact that the Real Gross Domestic Product (GDP) per capita was Higher in 1997
• Historians have Identified Two Dominant Currents in the Russian Women's Movement of the Late Tsarist Period.
• Some Historians Contend that Conditions in the United States During the Second World War
• Comparable Worth, as a Standard Applied to Eliminate Inequities in Pay
• The United States Government has a Long-Standing Policy of Using Federal Funds to Keep Small Business Viable.
• A Recent Study has Provided Clues to Predator-Prey Dynamics in the Late Pleistocene Era.
• Even More Than Mountainside Slides of Mud or Snow, Naturally Occurring Forest Fires Promote the Survival of Aspen Trees.
• The Black Death, a Severe Epidemic that Ravaged Fourteenth Century Europe
• The System of Patent-Granting, Which Confers Temporary Monopolies for the Exploitation of New Technologies
• Ethnohistoric Documents from Sixteenth-Century Mexico Suggesting that Weaving and Cooking were the Most Common Productive Activities for Aztec Women
• Solar Ponds are Bodies of Water in Which Circulation is Incomplete and There is a Very High Salt Concentration that Increases with Depth
• Traditional Social Science Models of Class Groups in the United States are Based on Economic Status
• Conventional Wisdom has it that Large Deficits in the United States Budget Cause Interest Rates to Rise.