training (the) quartet pt. 0: why four?

I say ‘training,’ but what follows will hover somewhere between exercises, tutorials and a kind of improv meet and greet. These are not autonomous ‘compositions’ or ‘works’: they were never designed for public performance. They are teaching tools and also a way to train/rehearse an improvisative ensemble together in a relatively short space of time. Relatively novice improvisers can spend upwards of ten weeks on these; experienced improvisers can run through these in a couple of afternoons. Either way, after a group has run through the exercises, the strategies and tactics presented will affect an ensemble's collective behavior in improvised performances—some of it good, much of it problematic (but more of that later).
Although I am, and will be, more-or-less responsible for the (bloggified) written account, I can’t claim any kind of exclusive authorship of these exercises. What I will be presenting was developed with PH, AMC, DW, KN, SCL, EK, WW, SR and others, and I’ve borrowed some additional tactics from work with POD and PR. (Apologies for the code names, but, with some luck, the individuals involved will recognize themselves.)Why quartets? Why not duos? Trios? Quintets? Sextets? Dectets? Why not improvising orchestras? The short answer is a variant of the Goldilock’s response: It ain’t too big, and it ain’t too small.Additionally, the quartet is the smallest unit in which you start getting interesting sub groupings. Trios too easily break down into solo-plus-accompaniment (1+2); duos are duos (2) or two solos (1+1); and solos are, well, solos (1). Quartets, on the other hand, can be reconfigured as six double-solos-plus-duos (1+1+2), four solo-plus-trios (1+3), three double-duets (2+2), one quadruple-solo (1+1+1+1), and one quartet (4).

some (unanswered) questions

Is there really something special about the quartet?
Do the qualities that I’ve attributed to the quartet ring true to you? Is that Goldilock’s response just lazy dogma on my part?

The straight man: how do quartets break down socially?
Has anyone else observed the phenomenon of the ‘straight man’ in a quartet? A individual who doesn’t hang-out in the same places, doesn’t share the same sense of humour, has distictive dietary requirements, tends to play ’bop licks more (or less) than the rest of the quartet?