  Biological genotypes do not code directly for phenotypes; developmental
physiology is the control layer that separates genomes from capacities
ascertained by selection. A key aspect is competency, as cells are not a
passive material but descendants of unicellular organisms with complex
context-sensitive capabilities. We used an evolutionary simulation in the
context of minimal artificial embryogeny to probe the effects of different
degrees of cellular competency on evolutionary dynamics. Virtual embryos
consisted of a single axis of positional information values provided by cells'
genomes, operated upon by an evolutionary cycle in which embryos' fitness was
proportional to monotonicity of the axial gradient. Evolutionary dynamics were
evaluated in two modes: hardwired "mosaic" development (genotype directly
encodes phenotype), and a more realistic mode in which cells interact prior to
evaluation by the fitness function ("regulative" development). Even minimal
competency with respect to improving their position in the embryo results in
better performance of the evolutionary search. Crucially, we observed that as
competency of cells masks the raw fitness of the genomes, the phenotypic
fitness gains are then mostly due to improvements of cells' developmental
problem-solving capacities, not the structural genome. This suggests the
existence of a powerful ratchet mechanism: evolution progressively becomes
locked in to improvements in the intelligence of its agential substrate, with
reduced pressure on the structural genome. A feedback loop in which evolution
increasingly puts more effort into the developmental software than perfecting
the hardware explains the very puzzling divergence of genome from anatomy in
species like planaria, identifies a possible drive for scaling intelligence
over time, and suggests strategies for engineering novel systems in silico and
in bioengineering.
