Killing of a sibling is the most extreme manifestation of sibling conflict. Siblicides can be either obligate or facultative. In species exhibiting obligate siblicide, sibling conflicts inevitably lead to the death of the other sibling. Whereas in facultative siblicide, heavily influenced by the prevalent environmental conditions, sibling conflict may occasionally lead to the death of a sibling. Although siblicide is rare among mammals and extremely rare among humans, facultative siblicide does occur.