INDIRECT GENE SELECTION. “In the process of evolution, selection may act directly on regulatory functions but only indirectly on gene sequences, which is supported by the experimental observations that some orthologous genes with highly conserved expression patterns have substantial divergence in their promoter sequence. That means that functional conservation does not necessitate conservation on the sequence level.”
https://genomebiology.biomedcentral.com/articles/10.1186/gb-2007-8-10-r225