PTSD-associated CpG sites that overlap the RNA polymerase II pre-initiation complex binding motifs evolved on the ape (cg10498097/MGC50811), primate (cg04033774/GPSM2 and cg20318748/NANP), and placental (cg24673765/HSPB6) stem lineages, while those that overlap with Beta2/NeuroD binding motifs evolved on the ape (cg04587829/FN3K) and primate (cg00427635/TBC1D21) stem lineages. This evidence concerns the gene TBC1D21 and post-traumatic stress disorder.