The recent spate of discussion surrounding the issue of sacral nutation/counternutation in the blogosphere had many a yogi/yogini bent all out of shape (no pun intended) trying to use differing terms to describe what is essentially the same phenomenon.
At the risk of stirring up still more... discussion, I'm going to share a few things related to this whole issue that will hopefully give us some interesting new perspectives.
First, a few totally useless factoids about the sacrum (courtesy of wikipedia, which is of course not a scholarly source, but then again, I'm not a medical doctor, so what the heck):
(1) The word "sacrum" is derived from the Latin sacer, "sacred", a translation of the Greek hieron (osteon), meaning sacred or strong bone.
(2) Since the sacrum is the seat of the organs of procreation, animal sacrums were offered in sacrifices.
(3) The sacrum is noticeably differently-shaped in males and females:
"In the female the sacrum is shorter and wider than in the male; the lower half forms a greater angle with the upper; the upper half is nearly straight, the lower half presenting the greatest amount of curvature. The bone is also directed more obliquely backward; this increases the size of the pelvic cavity and renders the sacrovertebral angle more prominent.
In the male the curvature is more evenly distributed over the whole length of the bone, and is altogether greater than in the female."
(4) There is much debate over this, but some evolutionary biologists believe that the sacrum is an evolutionary vestige: It served the useful function of stabilizing the tail back when our ancestors still had tails (hence "tailbone"), but no longer serves any function in the human body. As I mentioned, this is a very contentious issue, as there are at least an equal number of scientists who believe that the sacrum still serves a vital function by supporting certain internal organs and the perineal muscles.
Actually, factoid (3) is not totally useless to us yogis and yoginis. There is a longstanding myth in yoga circles that generally, yoginis tend to be more "backbendy" than yogis. Confession: I myself played a part in perpetuating this myth. Back in grad school, when I first started going to yoga classes, I would notice that almost all the people who were proficient in backbends in class were women. Over lunch after yoga class, a few fellow male yogis and I would exchange notes, and we all agreed that, for some reason, women generally seemed to be more backbendy. I wonder if (3) might lend some scientific basis to this myth (or not). Any thoughts on this?
Last but not least, I will end by saying something obvious: Whether we like it or not, the sacrum is here to stay. It's not going anywhere! So, we might as well celebrate its presence in our bodies. With this in mind, I have composed a poem (written pretentiously in old English) to celebrate this, uh, occasion:
Ode to the Sacrum
Hail Os Sacrum!
Thy Sacred Presence
Hath graced the spinal base of Homo Sapiens
For many a Millenium.
Thy workings hath been the source of constant wonder;
Might thou be an Evolutionary Vestige
Or is thy working yet shrouded in Mystery
Its full functioning to be revealed
To us mortal minds only with the passage of Time?
Art Thou a Boon or Bane
To the backbendy practices of many a Yogi and Yogini?
If Thou be a Boon
Wherefore art thy workings so Inscrutable and Unfathomable?
Wherefore do Yogis and Yoginis fall all over themselves
In valiant attempts to unravel the secret workings of thy Nutation and Counter-nutation?
If Thou be a Bane
Wherefore hath Evolution not acted sooner
To banish thy baneful presence from our all-too-mortal spines?