Poor posture over a person's lifetime. And improper lifting techniques can harm the back.
If many people in an office develop one, it can be stress related. Also, poor ergonomics of chair to desk heights can result in problems. Most couches and recliners offer poor support.
Also, abdominal weight gain (not just for pregnant women!) can also exacerbate the problem. Mild exercise, including walking, can help keep the back flexible as well as helping keep the extra pounds down. Unaligned posture