Any idea why so many words and phrases referring to a certain rigidity of personality, spring from roots associated with the same area of the human anatomy? I mean, of course:

costive
constipated
anal retentive
rectitude

slightly off-track:

fundamental

plus, of course, the other favoured use:

ers-hole (in Chaucerian spelling)

But it's the first group I am most intrigued about. And no, this is not meant to be a scatological thread.

well, as a starting point, the Latin root for constipate is constipatus, past participle of constipare,
to crowd together, from com- + stipare to pack tight.

I think you have to use your body to get the full feeling that the words imply. Breathe in, holding as much in as you are capable of (harder for some of us than others) then clench everything that can be clenched, then try to talk to yourself in the mirror. Then think of a word to describe yourself. Then I don't think you need to wonder why so many words and phrases referring to a certain rigidity of personality, spring from roots associated with the same area of the human anatomy.

>anal retentive<
Freudian, i think, to describe people who have never, in some ways moved past the issues they had with parents (mothers) about toilet training.

From a 2 years perspective, he/she can make mother happy by moving his/her bowels. by tightening up, and withholding, he/she can exersize some control over parent.. (but it is a sort of cut of your nose to spite your face action--even though analogy is from the other end of the anatomy)
Freud speculated that some people got stuck in mode of behavior that was akin to a 2 year old being anal retentive-- withholding normal functions and emotions, in order to try to control the emtions of other.

on the other end of the alimentary canal, mouth and lip, are used to describe people who often break (as least verbally) with authority. (wise mouth, "don't give me any lip, she (he) got lippy with me)

>the Latin root for constipate<

You may want to consider the Latin root of rectitude too - rectus, straight.

So two of your original list of four (key) words are from common and non-scatological roots that also have scatological derivatives. Looked at that way, there is a lot less coincidence going on here than first appears.

Reminds me of a wonderful book I have just finished (Why Flip a Coin? - The art and science of decision making) where the author talks about the human propensity to spot a pattern where none exists. (I recommend the entire book to anyone who gambles, invests or cares about voting and how governments are elected - which may be more than usual at this time!)

yes! and costive comes from the same root as constipate, and has gone from being a synonym for same to related senses: slow; stingy.