The difference between gene-expression estimates from multi- and single-species array analyses is plotted on the y-axis. Thus, positive values indicate that a greater difference was found in the multispecies analysis than in the single species one, while negative values point to the reverse. Probes are ordered by their log₂ expression difference, as estimated from the multispecies analysis (x-axis). (A) Human–human (for which the human and chimpanzee probes were used—mean absolute log₂ difference 0.07 ± 0.06) (B) Human–chimp (mean absolute log₂ difference 0.18 ± 0.16) (C) Human–orangutan (mean absolute log₂ difference 0.24 ± 0.21) (D) Human–rhesus (mean absolute log₂ difference 0.25 ± 0.20)