Spare a thought during the Christmas festivities, for those bloggers who explore the art-science interface. This is a difficult time of year for us, assaulted on all sides by anatomically-implausible depictions of angels. I have written previously about how the work of Renaissance artists such as Leonardo di Vinci was based on a deep understanding of human anatomy (see “”I am only teaching you how to see””) yet we find a liberal sprinkling of angels in their works. To be fair, Leonardo, to the best of my knowledge, only depicts angels in two early works (before his anatomical studies), but Titian and Tintoretto are repeat offenders (see “The Geography of Art” and “walking in Tintoretto’s shadow”).
I will, for now, by-pass the theology of angels, except to comment that the Bible never states that angels possess wings. Angels appear in both the Old and New Testaments as messengers from God, but we get no clues to their appearance. The appearance of angels in art owes as much to descriptions of Seraphim and Cherubim in the Old Testament, particularly the book of Ezekiel. Though these are very different to the angels we see in western art (and on Christmas cards), they do, at least, possess wings.
My faint memories of zoology lectures reinforced the idea of a basic four-limbed body plan in vertebrates which, in humans, is modified to two arms and two legs. Yet angels have six limbs and, when I started to think about the practicalities of this, my head soon started spinning. Our locomotion relies on the tensions generated as muscles encounter resistance from the bones to which they are attached. Adding two extra limbs to the abdomen of a human body plan requires upwards of a dozen new muscles each, all of which need points of attachment on bones, particularly the scapula (shoulder blade), clavicle (collarbone) and sternum (breastbone). Bear in mind, too, that a wing would require substantial muscles (as large as or larger than the thigh muscles) and, also, that the arrangement of both bones and muscles in birds is substantially different to that in mammals in order to facilitate flight. In particular, the pectoralis muscles is enormous, relative to the rest of the body (it’s the source of all that breast meat that your Christmas turkey yielded yesterday lunchtime) and it is also attached to a much larger sternum than the human model. This allows for a powerful downpull which helps the bird to fly. The upward motion of the wing is facilitated by the supracoracoideus muscles, which pulls on a tendon that loops over the furcular (“wishbone”) and around the scapula and finally attaches to the humerus in the upper part of the wing.
So our anatomically-correct angel needs to have a very highly-modified chest, and two sets of pecs, one set of which would be mightily impressive by the standards of the average fit human. If you passed an angel in the street, you might think (assuming that you did not notice the wings) that the guy was a body-builder, probably pumped-up on steroids. He could, quite possibly, be mistaken for a night-club bouncer. Just don’t try calling him “cherub”.