Abstract
Mechanisms underlying phenotypic divergence across species remain unresolved. In this issue of Cell Genomics, Hansen, Fong, et al.(1) systematically dissect human and rhesus macaque gene expression divergence by screening tens of thousands of orthologous elements for enhancer activity in lymphoblastoid cell lines, revealing a much greater role for trans divergence at levels equal to those of cis effects, counter to the prevailing consensus in the field.