regulatory genes have an average of 1.6 downstream connections. All
else being equal, nodes with more downstream connections such as
kernels here should be more conservative, because their activity can
bring more consequences. If they are changed, it is more likely that
something will go wrong. One model to explain this idea was
proposed by Riedl (1978). In this model, Riedl raised the idea of
“burden” which states that the evolvability of a character change
during evolution depends on the importance of the functions and
structures depending on it. The kernels of the gene regulatory
networks which determine the phylo-level body plan are thought to
have “heavier” burden than other parts of gene regulatory works,
since it is the base of animal body plan. So kernels are likely to be
more conserved.