Mr. Speidel gave the signal to open the cage door. Within seconds Unk was in the doorway, making his aggressive face at Suzy. The encounter was a precise duplicate of the earlier meeting: Unk attacked and Suzy tried frantically to get away. This time, however, the big male gibbon gave her no chance to escape. After what seemed like a very long two minutes, everyone realized that nothing would be accomplished by leaving the two animals together. In fact, it seemed essential to separate them quickly to prevent serious or fatal injury to Suzy.
The keeper had no intention of separating the gibbons with his bare hands. Although he outweighed Unk by a hundred pounds, Unk’s incredible strength was well-known, and any sensible human regarded the siamang’s teeth with respect. Tangling with an enraged Unk would have been foolhardy in the extreme.
Nevertheless, the keeper had to get Unk away from Suzy, and fast. He picked up a hose and turned on the water, directing a strong stream right at Unk through an opening at the bottom of the cage. Siamangs, like other apes, do not enjoy getting wet, and Unk was no exception. Immediately he forgot all about mauling Suzy. With no other objective than escaping the hateful spray, he dashed back into his own cage.
Meeting Number Two had proved as disastrous as the first. Most of the zoo staff despaired of ever getting the siamangs together. They could not continue to increase Unk’s tranquilizer dosage. Too much would make him sleep, and when he woke up, he was certain to be as bad-tempered as ever. Besides, only good luck had prevented injury to Suzy during the first two encounters. Sooner or later Unk was certain to hurt her. Nearly all the humans involved in the project wanted to give up.
George Speidel had to admit that the situation looked hopeless. Perhaps he should listen to advice and forget the idea of a pair of siamangs. He thought about the problem for weeks. But no solution came. Then one day he told the siamangs’ story to a friend, who suggested a completely new way of viewing Unk’s behavior.
Adult male siamang gibbons are normally bad-tempered toward unfamiliar animals. They have to be aggressive if they are to be successful defenders of a family territory in the jungle. In the wild, very docile male siamangs are probably not successful breeders. Unk, however, was far more aggressive than normal. After all, a wild male siamang without a mate should not attack an unmated female. If that were normal behavior, new siamang pairs would not be formed and the species would quickly die out.
Why was Unk’s behavior abnormal? Was it because he had been raised by humans, without a chance to learn normal siamang behavior? Perhaps he just did not know when aggression was appropriate and when it was not.
However, there was another possible explanation for Unk’s behavior. Perhaps his body produced male hormones in unusually large quantity. Hormones are substances produced in special glands in the bodies of animals (including humans). Some hormones are important in controlling physical processes such as growth and digestion. Some appear to affect behavior.
Most hormones are produced by animals of both sexes, but as few are produced only by females, a few only by males. Sex hormones help to create specific physical characteristics, but in animals whose behavior is largely controlled by hormones, sex hormones help to produce appropriate behavior as well. The ability of a female bird to lay eggs, for example, depends on female hormones, but so might her method of building a nest. Similarly, the ability of a male bird to fertilize eggs depends on male hormones, but so might his singing. In siamangs, aggression might well be dependent on the body’s production of male hormones. Too much aggression, as in Unk’s case, could mean that the body was overproducing male hormones.
The actions of hormones on animals’ bodies, and especially on animals’ behavior, are not very well understood, but biology researchers agree that male and female hormones often appear to counteract one another. Therefore, an animal’s overproduction of male hormones might be treated by giving him injections of female hormones. (No one has figured out how to make an animal’s body reduce its production of male hormones.)
