Mice don’t have tails on their backs, and their ribs don’t grow from lumbar vertebrae. And for a good reason. EPFL scientists have discovered the mechanism that determines the shape that many animals take – including humans, blue whales, and insects.
Why don’t our arms grow from the middle of our bodies? The question isn’t as trivial as it appears. Vertebrae, limbs, ribs, tailbone … in only two days, all these elements take their place in the embryo, in the right spot and with the precision of a Swiss watch. Intrigued by the extraordinary reliability of this mechanism, biologists have long wondered how it works. Now, researchers at EPFL (Ecole Polytechnique Fédérale de Lausanne) and the University of Geneva (Unige) have solved the mystery. Their discovery will be published October 13, 2011 in the journal Science.
via From whales to earthworms, the mechanism that gives shape to life.
Biosingularity 
How does this work?
Does the “HOX-clock” get copied at division with both copies synced at the same time?
The time is the unwinding of the DNA, how then can this be copied with cell-division?