Whichever one you still have is the one that’s left, ipso facto.
Wow. I am a monumental dork:
Developmental asymmetry is is difficult and has been achieved to any great degree only in endoderm germ layer derived tissues (mainly internal organs except heart and spleen). The urogenital tissues are derived from the mesoderm, as are the skeleton and skeletal muscle tissue (whole 'nother topic about how “good bone structure” (i.e., beauty) is a direct indication of having highly functional reproductive system due to the high quality of it’s development).
It’s more a matter that the savings associated with exploiting the cheap accessibility of symmetry can more than cover having an “extra” testicle. No bad reason not to have one, and having a spare comes in handy.
While there are some interesting anecdotes about testicles (e.g., they trade production back and forth so the other can get some rest- same has been observed of ovaries) there’s not a whole lot of common and persistent behavioural quirks like the ones asked about in the OP. A given individual might have significant differences. Or all individuals might occasionally have significant differences for short periods of time… but nothing you can really generalize about with much of a “Huh! How 'bout that?” factor. 'Least not that I’ve come across.
Because any more would make it hard to walk?
Nitpick: Enik wasn’t from the future…he was from the past!..the past!..the past!..
In dogs (and I wonder, maybe humans as well) a retained right teste is more common than a retained left due to the longer journey required for the right to reach its destination.
On investigation, right is more common in humans as well. Cite:
http://pedclerk.bsd.uchicago.edu/cryptorchidism.html
I’m not sure how “common” a belief this ever was. Injury to the genitalia in the rough and ready world of days gone by was common enough that it’s mentioned in the Bible as a specific exclusion for entering the Temple of Solomon. It remains common in more recent times, due to both accident and surgery. It’s just not commonly discussed today (but would have been hard to keep secret in the smaller, fixed communities of generations long past (when people generally lived and died in the same community)
Such individuals would have provided instant refutation. But of course, there’s no shortage of easily refutable beliefs, even in First World today.
I would say that the real reason for two testicles in humans is ontological, having to do with the anatomical origin of the testes in the embryo. That’s a bit of a chicken and egg problem: sexual reproduction almost certainly preceded bilateral symmetry, and I’m sure some organisms have developed [retained?] a single midline structure.
I don’t think that it has a “reason” in the sense that Homo sapens outcompeted a race of one-balled men on the battlefield of fitness (or the equivalent at some ancient stage of evolution) A lot of the details of our construct “just happened”, and worked well enough to be the substrate for subsequent refinement.
I don’t know. I would probably think of it as the right one for me.