(2) Swellings vary in size within an individual across cycles. Females of most primate species PF2341066 repeatedly before conceiving. In chimpanzees and baboons, where sexual swellings have been the most intensively studied, maximal swelling size increases from cycle to cycle within one individual (Deschner et?al., 2004, Emery and Whitten, 2003, Fitzpatrick et?al., 2014 and Higham et?al., 2008b). This type of variation may signal differences in the probability of conception across cycles. Although variation in conception probability from one cycle to the next has not, to our knowledge, been described empirically for any species, data from our study population suggest that the cycles immediately following postpartum amenorrhea are less likely to result in conception than later ones (data presented in Fitzpatrick et al., 2014). Furthermore, in four populations of baboons (three wild and one captive), alpha males were shown to successfully target conceptive cycles, further suggesting that, within a given female, cycles vary in the probability of conception (Alberts et?al., 2006, Bulger, 1993, Daspre et?al., 2009, Gesquiere et?al., 2007 and Weingrill et?al., 2003).