Asa general rule, the larger a social group of primates, the more time its members spend grooming one another. The main purpose of this social grooming is the maintenance of social cohesion. Furthermore, group size among primates tends to increase proportionally with the size of the neocortex, the seat of higher thought in the brain. Extrapolating upon the relationship between group size and neocortex size, we can infer that early human groups were quite large. But unexpectedly, there is strong evidence that, apart from parents grooming their children, these humans spent virtually no time grooming one another. Which one of the following, if true, would do most to resolve the apparent discrepancy described above? ['Many types of primates other than humans have fairly large neocortex regions and display frequent social grooming.', 'Early humans were not as extensively covered with hair as are other primates, and consequently they had less need for social grooming.', 'While early humans probably lived in large groups, there is strong evidence that they hunted in small groups.', 'Early humans developed languages, which provided a more effective way of maintaining social cohesion than social grooming.']