Yawn contagion occurs when one individual yawns in response to another’s yawn. Studies of this behavior in primates have
focused on populations in captivity, but biologist Elisabetta Palagi and her colleagues have shown that it can occur in wild
primate populations as well. In their study, which focused on a wild population of gelada monkeys (Theropithecus gelada) in
Ethiopia, the researchers further reported that yawn contagion most commonly occurred in males and across different
social groups instead of within a single social group.
It deﬁnes a phenomenon that is discussed in the text.
It introduces a problem that is examined in the text.
It makes a claim that is challenged in the text.
It presents a hypothesis that is evaluated in the text.
Choice A is the best answer because it most accurately describes how the ﬁrst sentence functions in the text as a whole.
The ﬁrst sentence introduces what yawn contagion is, explaining that it occurs when an individual yawns in response to the
yawn of another individual. The text goes on to describe Elisabetta Palagi and her colleagues’ study of this phenomenon in a
wild population of gelada monkeys. According to the text, the study showed that wild primate populations experience yawn
contagion and that the behavior occurs most commonly in male monkeys and across social groups. Thus, the function of
the ﬁrst sentence is to deﬁne the phenomenon of yawn contagion that is discussed in the text.
Choice B is incorrect. Although the ﬁrst sentence introduces the text’s discussion of yawn contagion, it doesn’t present this
behavior, or anything else, as a problem. Choice C is incorrect because the ﬁrst sentence doesn’t present a claim but instead
explains what yawn contagion is. Moreover, the text doesn’t challenge anything; it’s an informative text that describes the
ﬁndings of a research study about yawning in wild primate populations. Choice D is incorrect. Although the text describes a
scientiﬁc study, and most scientiﬁc studies are guided by a hypothesis, the text doesn’t say what Palagi and her colleagues’
hypothesis was; the text discusses their ﬁndings instead.