Scientitsts at the University of North Carolina believe that laziness might have genetic precursors. Labratory studies in mice have shown that there is a link between certain genomic locations and how far these mice are willing to run. They believe that there might be human analogs which could help to explain laziness.

From Time,

"Exercise-prone mice put in a good 5 to 8 miles per day (the equivalent of an average man running 40 to 50 miles a day), versus 0.3 mile per day for inactive mice. While the exercise wheels of the activity-prone mice would turn all night, some of the sedentary mice devised ingenious ways to avoid activity. One stuffed wood shavings around the wheel and turned it into a bed; one used it as an, ahem, toilet; and one climbed on top of her wheel only to get a better look at the overhead sensors tracking her movements."