Early birds who rise at sun-up, and smugly suspect that everyone could if they had enought drive, may be ignoring genetic differences decreed by nature, The first findings to link genes with the human body clock are reported in a new study by Emmanuel Mignot, a sleep expert at Standford Medical School in Palo Alto, California . A mutation on a Chromosome 4 gene dubbed the Clock gene in mammals because it helps regulate their body clocks helps determine preference for morning or night activity, Mignot says.