• New Study shows that different coloration of primates doesn’t indicate fertile phases, but individual characteristics and reproductive status.
  • Previous studies of ornamentation in female primates have focused mostly on the fertility signaling function of the female anogenital male attraction and female to the female competition.
  • The study aimed at determining if skin coloration changes actually signify the probability of conception in selected female macaques.
  • In summary, the result of the study shows that this color ornamentation shows social status rather than accurate sexual signaling.


Quick Summary

A new study from a team of Kyoto University’s Primate Research Institute published in Behavioral Ecology and Sociology proposes that the Japanese macaques’ red skin coloration denotes social rank rather than fertility.


The research team hoped to understand better human sexuality by examining the biological and evolutionary roots of sexual communications of primates.

While previous studies have primarily focused on the coloration of the female anogenital, which was thought to act as a fertility signal to attract males. This study provides more insight that information contained in this color signaling has to do with social rank.


The study team in a bid to have accurate results analyzed 12 in-captive female Japanese macaques. These Macaca fuscata’s were analyzed in the variation of their hindquarter and facial coloration (luminance and redness) in timely according to the fertile phase, the cycle number and also whether the cycle was non-conceptive or conceptive. This was analyzed with their individual characteristics like parity, social rank, and body mass.


The hindquarter and facial coloration don’t accurately propose the timing of the primate’s fertility phase, while the hindquarters luminance variation indicated differences between the different ovulation stages.

The faces became lighter while the hindquarters turned less red as the successive cycles increased. The hindquarters of these primates became redder during non-conceptive cycles as compared to conceptive ones.

In good lighting, the skin luminance and redness appear perceptible. Darker hindquarters can be seen on top-ranking females. Also, the study found that color variations might contain information relating to body mass differences but not in parity.

The female Japanese macaques’ coloration might be indicative of specific female characteristics and inter-cycle variation rather than their fertile phase.


  • The study focused only on in-captive female Japanese macaques and not the wild and free ones.
  • The study adds to a growing list of other scientific studies about female coloration, and it’s contained sexual information which is susceptible to additional research.