Concept of Burden in Evo-Devo

The concept of burden was developed around the 1970s by Austrian zoologist Rupert Riedl, based on morphological insights rooted in Karl Ernst von Baer’s embryological tradition. Burden’s main tenet is that as a morphological character evolves, it develops more relationships with other characters, becoming more and more interconnected. Through this process, the morphological character acquires more biological “responsibilities” within the organism. Two main consequences of the burden hypothesis are that (1) a character’s evolvability will be limited by these responsibilities and (2) a set of heavily burdened characters could be considered as part of the body plan of a taxonomic group. The concept of burden is intimately related to that of developmental constraint, and as such, it is central to evo-devo.