Monkeys and their psychologies
Harry Harlow settled on rhesus macaques as psychological subjects because they were more hardy and tolerant to his experimental whims.
Our most fundamental reason for selection of the rhesus monkey as a standard test primate lay in the fact that we had gradually come to appreciate their behavioral capabilities in informal test situations. Although these monkeys are almost devoid of personality, in the common sense meaning of the term, they are stable and dependable test subjects, that tame rather readily and adapt to experimental test conditions in a highly satisfactory manner. The rhesus monkey lacks the gay abandon of the cebus monkey, the elegant grace and composure of the spider, or the buffoonery of the chimpanzee. But beneath the gray or grim exterior of the rhesus is a central nervous system waiting to grind out a hundred test trials a day. The difference between a cebus monkey and a rhesus is all the difference between a southern belle and a New England store keeper. Our primary interests concerned learning and intelligence.
Rhesus monkeys are definitely not "devoid of personality" (Harlow's later researchers showed that they are full of it), but he is spot on that an informal appreciation of your study subjects elbows and jostles your project along. Rather than being a too-tangy relish overpowering what is really there in an animal's behavior, a tinge of anthropomorphism is the sweet flavor that gives meaning and motivation to our work.
