HUMAN EVOLUTION 



that the extended dependency characteristic of human children 

 could develop in a society without food sharing. The amount 

 of information which needs to be transduced in a communica- 

 tion system for plant eaters, a group in which each mammal 

 gets his own food, is small compared to that needed in a group 

 which cooperates in the hunting of large animals and bringing 

 the resultant food to a central place for distribution among sub- 

 ordinate members of the group. The food-getting behavior of 

 Pleistocene hominids puts a premium on social behavior. This 

 brings us to a biological factor important in the social organi- 

 zation of primate groups. 



5. Cortical Control of Sexual Behavior 



On a fundamental biological level sex, obviously, has the 

 same function in the human species as in other mammals: it is 

 the way new members are recruited into the species, and it 

 provides the genetical advantages of gene recombination. On 

 the social level sexual behavior offers one of the strongest con- 

 trasts between non-human primate and human behavior. Here, 

 however, as in many other biological characters, the behavior 

 of man is less distinct from that of the apes than the behavior 

 of the apes is from that of other mammals. In the majority of 

 mammals, sexual behavior is seasonal, and the mating periods 

 correspond to times when the female has a high probability of 

 ovulation and conception, since the reproductive physiology is 

 timed so that births occur during a period when the maximum 

 amount of food is available for the newborn. In such mammals, 

 including the lower primates, copulation is invoked by the re- 

 lease of gonadal hormones in the body fluids. In animals with 

 sexual seasons we can induce copulation out of season by hor- 

 monal injections or prevent copulation in season by gonadec- 

 tomy. The living primates fall into a graded series according 

 to the degree of hormonal control of sexual behavior. In man 

 and the chimpanzee, and probably also in the other pongids, 

 copulation is strongly under cortical control and is not pre- 

 vented by gonadectomy (Ford and Beach, 1951). 



An important primate adaptation for culture is the change 

 from wired-in reflex pathways to neural connections over as- 



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