Interspecies comparison produced by the VISTA server [37, 38], highlighting conserved elements. The conservation profiles were obtained with the human sequence as reference (chromosome 6, human genome build 34, megabase coordinates as indicated on the horizontal axis, in an intergenic region). The percentage identity was computed in sliding 100 bp windows by comparison with five different species. Frog is Xenopus tropicalis, and fish is Fugu rubripes. Arrows indicate: (a) an element conserved in mouse, frog and chicken, but not in rat; (b) ultraconserved element uc.196  (221 bp, 100% conserved in mouse and rat); (c) an element conserved in all five species down to fish. The somewhat arbitrary conservation relationships (for example, a segment highly conserved between human and frog but not found in rat) is indicative of a stochastic process, in line with notions embodied in Figures 4 and 5.