You know, the pregnancy idea is one I've only heard once before, and that was in relation to some carvings at Buttony in Nbland, where it was suggested that they looked distinctly as if the carver was female. The idea was even put forward that the rings represented the number of finger widths needed to describe vulvic dilation, and that this explained why there are hardly ever more than 8 rings.

It got linked in with placement in the landscape by charting the multiple ringed motifs with caves or rockshelters that would have made suitably safe places to give birth, free from depredations of wolves etc. It was also pointed out that this may not have been anything to do with human birthing, and could have formed a part of the initial stages and passing on of oral lore regarding animal midwifery in the early days of domestication of animals, hence the frequent occurrence in areas of transhumanant activity.

All quite compelling in one way, but whilst it sort of works for some areas of Nbland, it falls flat on it's face when applied to Yorkshire, Cumbria, Kilmartin or even southern Northumberland.

But it should be added to the list :) As far as I know, no-one has compiled a definitive update of Morris' original 100. If anyone here on TMA (or anywhere else for that matter, including universities and Stan Beckensall's house) would know, it'd be RockArtUK. He might pop up here at some point.