I examined 320 specimens from 27 species of canids (Canidae, Carnivora, Mammalia) (Table 1). All species were examined to clarify evolutionary patterns in relative molar sizes. The dietary pattern of each species was categorized as carnivorous (primarily eating mammalian flesh), omnivorous (eating various foods, with neither mammalian flesh nor insects comprising >50% of the diet), or insectivorous (primarily eating insects) using information from the literature (Sillero-Zubiri 2010). In order to estimate variability in molars, I examined individual variation in relative molar sizes. For this purpose, individual variation within seven species was examined whereby I measured >15 individuals from each species (Table 1, 2). In addition, I examined individual variation in the presence or absence of M3 in Vulpes lagopus and Nyctereutes procyonoides to clarify whether individual variation and missing of M3 are explained by the inhibitory cascade model. The specimens of N. procyonoides examined were those deposited in Kyoto University Museum, Kyoto University, Japan, which had been collected from a small island, Chiburi Island, Shimane Prefecture, Japan. Specimens of the other species were those deposited in the Department of Mammalogy, American Museum of Natural History, USA, which had been collected from large areas. I measured the size of each molar as the projected area in photos taken from the occlusal view using ImageJ software (NIH, Bethesda, MD), and compared the relative molar sizes in the morphospace: M2 size/M1 size versus M3 size/M1 size (abbreviated as M2/M1 vs. M3/M1) (Kavanagh et al. 2007). Any given point in morphospace represents the relative sizes of the three molars of a particular species or individual. I plotted the average values for each species to describe interspecific variation, and plotted each individual to describe individual variation. Reduced major axis (RMA) regressions were performed on these plots after performing Anderson-Darling normality test. I used M2/M1 as an index of activation versus inhibition during molar development. M2/M1 scores between carnivorous and omnivorous species were compared using the Mann–Whitney U test. Further, for V. lagopus and N. procyonoides, M2/M1 scores were compared between normal individuals and individuals that were missing M3 on one or both sides. Statistical analyses were performed using Minitab 14 (Minitab, Inc., PA), and RMA regressions were performed using PAST (Hammer et al. 2001). Several studies have utilized multiple regressions to elucidate how absolute molar sizes affect one another (Renvoisé et al. 2009; Wilson et al. 2012). However, this method tends to reflect variability in the absolute size of M1, and activation versus inhibition patterns can become obscured. Therefore, I focused on relative molar sizes, that is, the inhibitory cascade.