Common chimpanzees, bonobos, gibbons and baboons exhibit forms of bipedalism. Chimpanzees and bonobos are equally humanity's closest living relatives. Chimpanzees, bonobos, and gorillas eat the fruits of "Aframomum angustifolium". The zoo has bred and maintained bonobos (pygmy chimps) since 1960. Recent studies show that there are significant brain differences between bonobos and chimps. This indoor building features a large troop of bonobos and gorillas. Adult female bonobos are somewhat smaller than adult males. Takayoshi Kano observed similar practices among bonobos in the natural habitat. These bonds made between females are for protection against male bonobos. This dynamic is similar to the mating system of bonobos. Adult male bonobos have sex with infants, although without penetration. Sexual interaction has also been witnessed in female bonobos to avoid aggression. Immature bonobos, contrariwise, perform genital contact when relaxed. One study analyzed sounds made by human babies and bonobos when tickled. Its tibial and tarsal lengths indicate a leaping ability similar to bonobos.