Science: The Too-Warm Dinosaur

If heat can sterilize a bottle and a surgical instrument, why can't heat sterilize a man? A scientist who thought up this murky question, and has been brooding over it, is Biologist Raymond B. Cowles of the University of California at Los Angeles.

Dr. Cowles began by asking himself: why did the dinosaur become extinct? Dismissing the usual theories (the dinosaur's unwieldy size, an increase in the earth's carbon dioxide, etc.) Dr. Cowles decided that it was much more likely that dinosaurs simply perished of a declining birth rate—just stopped breeding during an interglacial heat wave. Last week he was ready to document his theory that there is a definite relation between heat and male fertility.

For reasons which biologists do not clearly understand, male sperm is extremely sensitive to heat, is quickly destroyed even at body temperature. In many animals (notably man), sperm is protected by a special cooling system in the scrotum which keeps it at 2 to 15° below normal body temperature. Experimenters have caused temporary sterility in dogs, rabbits, cats and bulls by artificially heating their testes; Australian sheep breeders recently reported that a sterile breed of rams became fertile when a thick growth of wool on their testicles was sheared off.

Dr. Cowles noted that the English sparrow apparently mates only during the cool early morning hours when its body temperature drops below normal. The garter snake rarely breeds in summer.

Dr. Cowles reasoned that the unadaptable dinosaur, lacking a cooling system, became sterile during a cycle of warm weather. To test his theory, he tried heat treatments on a descendant of the dinosaur, the night lizard (Xantusia vigilis).

A week in a 97° climate made the lizards sterile for a whole season; 100.5° sterilized them permanently.

Avoid the Noonday Sun. All this, thinks Dr. Cowles, may be a warning to man. He cites the fact that high fever sometimes causes temporary human sterility. A 1943 survey in Galveston, Tex. showed that the rate of conception of babies is higher in cool seasons than in warm. Other investigators have reported that the fertility of white men is greatly reduced in the tropics, and even natives conceive fewer children in the hot months. Dr. Cowles believes it entirely possible that a sustained cycle of hot climate on the earth might radically change or even wipe out the human race.

Much the same conclusions were reached independently at almost exactly the same time by a London scientist, H. Chapman Pincher, who reported his studies of temperature and male fertility in the British magazine Nature.

Tests were made on a group of healthy young men kept in a steam cabinet at 110° Fahrenheit for half an hour. After 18 days, their sperm counts fell well below the minimum for fertility, and they remained sterile for 67 days. Dr. Pincher, following up this study, investigated hospital and domestic bath temperatures which range from 105 to 110°. Putting two & two together, he suggested that the modern hot bath habit may be largely responsible for the declining birth rate in "civilized" countries.