[loorinm]

I haven’t seen anyone posit a theory as to why Western people bend this way, so I’ll go:

Extreme sex and body shame.

We receive, from a young age, shame about exposing - even with clothing on - “sexual” parts of the body - breasts, butt, and crotch.

Women are strongly motivated to tuck in the backside because it is both shamed and unsafe in our society to stick out our butts. This is why women squat to tie their shoes in public. Rape, assault, catcalling, is so prevalent and a constant awareness for women in public. This pose would also be considered “unprofessional” in a workplace.

Men are discouraged as well, lest they incur the worst male insult in our society : “gay”. Men are shamed and called gay from childhood if they take this hip-hinge pose. So they stop.

Bending at the waist exposes the vulnerable backside in a way that is unsafe in historically Puritanical Western society.

[jeffdavis]

It seems like you are reaching pretty far for a social explanation. It seems more reasonable to start with lifestyle and work style. Maybe lots of sitting and standing are to blame? Maybe something about industrialization or household conveniences (washing machine, etc.)?

I suppose there are some social factors, but I would assume they are secondary unless I see evidence otherwise.

[loorinm]

I don't think I'm reaching. Read the comments below, about the fact that children learn this spine-bend posture early on, way before any sedentary lifestyle. I'm pretty sure 3-year-olds aren't using washing machines either.

I'm speaking from firsthand personal experience, and overwhelming experience seeing others go through the same cultural conditioning I described in my post.

[jeffdavis]

How is 3 years old "way before any sedentary lifestyle"? I consider my family moderately active, but my 3 year old is certainly familiar with the couch. In more agrarian societies, there are probably a lot fewer opportunities to sit somewhere comfortably.

And did you consider agrarian but sexually-conservative regions (maybe India or the Middle East?), or developed but sexually-liberal regions (maybe Mediterranean?), to see if those line up with your theory?