When we look at the spine from the back, we see a straight column that is formed by the arrangement of vertebrae on top of each other and passes through the exact center of the head and pelvis. However, when we look at the human spine from the side, we see that there is no such straight line and that there are physiological curvatures formed by each vertebra making an angle with each other. For example, while we have a kyphosis (hump) in our chest and back region, we have a hollow in our following waist region.
The degree of kyphosis in the chest and back region varies widely among individuals. In other words, as you observe around you, some people have a more hunched posture while others stand more upright. There is a quantifiable physiological limit to this hump.
In a lateral radiograph taken in a comfortable standing position, this limit varies between 20 degrees and 55 degrees when measured at an angle. In other words, a person with a kyphosis of 20 degrees and a person with a kyphosis of 55 degrees are both considered within the normal limits of kyphosis. Therefore, it is perfectly normal for one member of a family to be more or less hunched than another.