Tips about Squats

Different people have varying femur and tibia lengths. Those with a longer femur tend to require a slightly wider stance to maintain an upright position during a squat.
 
The distance from the axis lengthens more dramatically as the knees bend and in order to compensate and keep the weight centered, they bend at the hips when a narrower stance is used.
Know your body structure and work with it, not against it.