A baby's circadian clock is fully formed before he's born, but until he's 2 to 5 months old, his brain isn't mature enough to fully respond to it. By then, he'll sleep more like you do -- for at least five to six hours at a time at night.
But you can foster the process. "Expose your baby to normal light and dark cycles," he says. "Just because a newborn developed in the dark environment of the womb doesn't mean he needs it that way now!" When he wakes up in the morning, feed him in a well-lit room. In the evening, dim the lighting. This will reinforce his circadian clock and help him establish a good daily rhythm. Keep up this pattern through his first few months.