The spine has no curvature at birth. The midback gradually develops quite a fixed forward hunched curvature in young childhood. Early on in development a flexible neck arch develops from the infant starting to raise its head while lying on its stomach and crawling around on all four limbs.
The flexible lower back curvature starts to develop at the end of the first year when the child starts to walk. These curvatures give springiness/shock absorbance flexibility and the ability to maintain a good standing posture.
When we get dysfunction, rigidity, and degenerative changes in the spine often these healthy curvatures in the neck and lower back diminish or even disappear completely.
As funny as it may sound an argument could be made for restoring neck health by arching the neck up while being on all four (like a baby) and re-stimulate the musculature that helped the healthy neck curvature to develop in the first place. Similarly squatting, lunging, cruising along furniture in a half squat might be helpful in re-habilitate the lower back and pelvis.
A common cause of de-generation of the muscular-skeletal system is lack of use or low variety of movements over repetitive work tasks. The key is to get back to frequent, varied movements in a healthy functional movement pattern like what the growing child instinctively does.