A paper by Dr. Trut discussing these changes, translated from Russian, was published in the current issue of American Scientist, the magazine of Sigma Xi, a scientific research society. Dr. Trut wrote that by breeding the tamest animals from each of about 35 successive generations, the final offspring were not only tame from early puppyhood but also looked different from their wild forebears.

The normal pattern of coat color that evolved in wild foxes as camouflage changed markedly in the genetically tamed fox population, with irregular piebald splotches of white fur appearing in some animals. The tame foxes sometimes developed floppy ears in place of the straight ones of wild foxes. The domesticated foxes generally had shorter legs and tails than ordinary foxes, and often had curly tails instead of straight, horizontal tails.

Moreover, the faces of adult tame foxes came to look more juvenile than the faces of wild adults, and many of the experimental animals developed dog-like features, Dr. Trut reported. Although no selective pressures relating to size or shape were used in breeding the animals, the skulls of tamable foxes tended to be narrower with shorter snouts than those of wild foxes.

Even reproductive cycles changed in foxes bred to be docile; wild vixens are receptive to sex only once a year, but some of the docile females become receptive more often.

Domestication also apparently affects genes controlling the timing of physiological development. For example, the genetically tamable fox puppies open their eyes sooner after birth than do ordinary silver foxes, and they show a fear response to unfamiliar stimuli about three weeks later than their wild counterparts.

Over successive generations and increasing congenital tameness, Dr. Trut wrote, the Russian team measured a steady decline in the hormone-producing ability of the foxes' adrenal glands. Adrenal hormones prepare an animal for fight or flight.

Even the brain chemistry of the tame animals differed from that of their wild ancestors; after 12 generations of selective breeding, Dr. Trut reported, test animals' brains contained significantly higher levels of serotonin than did their forbears. Serotonin, a neurotransmitter, is intimately involved in an animal's psychological state.