in their natal clan. Alliances between males are poorly developed in most bonobo communities, while females will form alliances with each other and alliances between males and females occur, including multisex hunting parties. There is a confirmed case of a grown male bonobo adopting his orphaned infant brother. A mother bonobo will also support her grown son in conflicts with other males and help him secure better ties with other females, enhancing her chance of gaining grandchildren from him. She will even take measures such as physical intervention to prevent other males from breeding with certain females she wants her son to mate with. Although mothers play a role in aiding their sons, and the hierarchy among males is largely reflected by their mother's social status, some motherless males will still successfully dominate some males who do have mothers. Female bonobos have also been observed fostering infants from outside their established community. Bonobos are not known to kill each other, and are generally less violent than chimpanzees, yet aggression still manifests itself in this species. Although female bonobos dominate males and selectively mate with males who do not exhibit aggression toward them, competition between the males themselves is intense and high-ranking males secure more matings than low-ranking ones. Indeed, the size difference between male and female bonobos is in fact more pronounced in bonobos than it is in chimpanzees, as male bonobos do not form alliances and therefore have little incentive to hold back when fighting for access to females. Male bonobos are known to attack each other and inflict serious injuries such as missing digits, damaged eyes and torn ears. Some of these injuries may also occur when a male threatens the high ranking females and is injured by them, as the larger male is swarmed and outnumbered by these female mobs. Due to the promiscuous mating behavior of female bonobos, a male cannot be sure which offspring are his. As a result, the entirety of parental care in bonobos is assumed by the mothers. However, bonobos are not as promiscuous as chimpanzees and slightly polygamous tendencies occur, with high-ranking males enjoying greater reproductive success than low-ranking males. Unlike chimpanzees, where any male can coerce a female into mating with him, female bonobos enjoy greater sexual preferences and can rebuff undesirable males, an advantage of female-female bonding, and actively seek out higher-ranking males. Bonobo party size tends to vary