Like obesity, alcoholism and voting Republican, laziness now has a genetic explanation. Maybe. The research is still as preliminary as the draft of your great American novel but, according to Time, an unimprovably named scientist, J. Timothy Lightfoot, has "identified 20 different genomic locations that work in tandem to influence activity levels in mice." The alpha rodents ran 5 to 8 miles a day on the treadmill (the equivalent of the 40-50 or so miles that Barack Obama runs), while the betas did more creative things with their workout equipment, such as turn it into a bed or toilet, or use it to get a better look at the weird machines monitoring their every non-movement. As ever, my money's on the inquisitive fatty.
[G]enes may affect either the way muscles work — perhaps causing them to use energy more efficiently and preventing fatigue — or some higher-order biochemical circuit in the brain, such as levels of the neurotransmitters dopamine or serotonin. Researchers have examined the muscle tissue of the mice in the study, however, and early data, which has not yet been published, suggests there's no difference in their function. So researchers' best guess is that the drive to exercise is at least partly influenced by brain chemicals...
Not to worry. Natural born sluggards can still smoke themselves thin.
[Time]