Infants younger than six months who have normal hearing can readily distinguish between acoustically similar sounds that are used as part of any language -- not only those used in the language spoken by the people who raise them. Young adults can readily distinguish between such sounds only in languages that they regularly use. It is known that the physiological capacity to hear begins to deteriorate after infancy. So the observed difference in the abilities of infants and young adults to distinguish between acoustically similar speech sounds must be the result of the physiological deterioration of hearing. The reasoning in the argument is flawed because the argument ['does not explain the procedures used to measure the abilities of two very different populations', 'takes a factor that might contribute to an explanation of the observed difference as a sufficient explanation for that difference', 'sets an arbitrary cutoff point of six months for the age below which infants are able to distinguish acoustically similar speech sounds', 'assumes that what is true of a group of people taken collectively is also true of any individual within that group']