Spiders have separate male and female sexes. Birds have two sexes&colon; either female or male. Learning capacities sometimes demonstrate differences between the sexes. Rules do not differ between the sexes. Lastly, there are differences between the sexes. This is due to the differences that occur between populations, sexes, and age groups. It is equally common in both sexes. Albinism usually occurs with equal frequency in both sexes. He held that "just relations between the sexes" involved women acknowledging their "inequality" with men. Macaque groups tend to contain a number of adults of both sexes. There were also marriages based on mutual consent of both sexes. Intermingling of the sexes is not permitted. There are several stories of depicting love between same sexes especially among kings and queens. Mixed groups contain animals of both sexes. There is little to visually distinguish between the sexes.