Parallel bottlenecks were proposed to exist among chimpanzees, gorillas, rhesus macaques, orangutans and tigers. Two examples of systems in primates are promiscuous mating chimpanzees and bonobos. Pygmy chimpanzees (bonobos) share many physical characteristics with humans. However, chickenpox has been caused in other primates, including chimpanzees and gorillas. Informally, "monkey" may refer to apes, particularly chimpanzees, gibbons, and gorillas. These include primates such as chimpanzees, some dolphin communities, and crows. Female Bili apes have genital swellings similar to other chimpanzees. He saw similarities between this environment and the habitat of the chimpanzees and gorillas. A 2014 study also found bonobos to be less aggressive than chimpanzees, particularly eastern chimpanzees. Scoliosis has not been found in chimpanzees or gorillas. The canines are ape-like but reduced, like those found in Miocene apes and female chimpanzees. It walks on its front knuckles similar to gorillas and chimpanzees. This view is supported by studies of higher apes, particularly chimpanzees. The sounds used for the monkeys were actually those of chimpanzees and siamangs. The current primate exhibit features chimpanzees (Pan troglodytes).