Researcher: People are able to tell whether a person is extroverted just by looking at pictures in which the person has a neutral expression. Since people are also able to tell whether a chimpanzee behaves dominantly just by looking at a picture of the chimpanzee' s expressionless face, and since both humans and chimpanzees are primates, we conclude that this ability is probably not acquired solely through culture but rather as a result of primate biology. Which one of the following, if true, most strengthens the researcher's argument? ['Some of the pictures of people used in the experiments were composites of several different people.', 'People are generally unable to judge the dominance of bonobos, which are also primates, by looking at pictures of them.', 'Any common ancestor of humans and chimpanzees would have to have lived over 7 million years ago.', 'Extroversion in people and dominant behavior in chimpanzees are both indicators of a genetic predisposition to assertiveness.']