Light on Sex

Even schoolboys know that birds mate in the spring, but even a bright schoolboy could hardly tell why. Biologist James C. Perry of Cincinnati's Xavier University, no schoolboy by a long shot, was convinced last week that it is not so much the flowers that bloom in the spring as what birds eat that affects their mating cycle. Other investigators had advanced the theory that increased exposure to sunlight in the spring is the sex stimulus. This theory they checked experimentally by inducing sex gland activity with artificial illumination. It looked as if the light stimulated the front lobe of the pituitary ("master gland"), which in turn roused the gonads.

In his laboratory Dr. Perry induced unseasonable sex activity by shining ordinary 25-watt lamps on sparrows much less than a year old. The beaks of the males turned dark and their testes developed spermatozoa; the ovaries of the females were swollen, contained numerous eggs. The scientist evoked even more pronounced gland changes with ultraviolet light.

Though some connection between light and sex was thus made obvious, Dr. Perry was not convinced that it was a case of cause and effect. Perhaps, he reasoned, the radiation first altered some factor in the diet, which then stimulated the pituitary and through it the sex mechanism. With this hypothesis in mind. Perry irradiated whole-wheat grains with ultraviolet light, fed them to his birds. That did the trick, whereas the sex glands of other birds which received the same (normal) illumination, but did not eat the irradiated, aphrodisiac wheat, remained in the "resting condition."

In the Proceedings of the Society for Experimental Biology and Medicine, Dr. Perry concluded: "This interpretation, which . . . shifts the emphasis from light affecting the animal to light producing a change in the diet, may well apply to the seasonal sexual development of other vertebrates as well.* The results . . . point to an increase of Vitamin D or some kindred substance as the specific dietary factor."

*Not including man, since human beings engage in year-round sex activity.

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