[Control of limb morphogenesis by the Hox genes]

Vertebrate limbs are an amazing example of successful adaptation to various environmental conditions. In higher vertebrates, forelimbs help to fly, swim, walk, dig or grasp, yet their basic structure (the sequence and spatial arrangement of bony elements) is always the same. This implies the existence of a unique developmental strategy for building a limb (a limb plan) that imposes early on a basic scheme, on the top of which subsequent species-specific customizations will occur. The description of such a universal limb plan, hence the idea that the genetic and developmental processes that generate this plan are very ancient, has been controversial for about a century. It is worth asking whether recent discoveries of important genes involved in these processes can bring novel arguments to the debate.