The mane of the male lion, unique amongst cats, is one of the most distinctive characteristics of the species. It makes the lion appear larger, providing an excellent intimidation display; this aids the lion during confrontations with other lions and with the species' chief competitor in Africa, the spotted hyena. The presence, absence, color, and size of the mane is associated with genetic precondition, sexual maturity, climate and testosterone production; the rule of thumb is the darker and fuller the mane, the healthier the lion. Research in Tanzania also suggests mane length signals fighting success in male-male relationships. Darker-maned individuals may have longer reproductive lives and higher offspring survival, although they suffer in the hottest months of the year. In prides led by a coalition of two or three males, it is possible that lionesses solicit mating more actively with heavily maned lions.
Scientists once believed that the distinct status of some subspecies could be justified by morphology, including the size of the mane. Morphology was used to identify subspecies such as the Barbary lion and Cape Lion. Research has suggested, however, that environmental factors influence the color and size of a lion's mane, such as the ambient temperature. The cooler ambient temperature in European and North American zoos, for example, can result in a heavy mane. Thus the mane is an inappropriate marker for identifying subspecies. However the males of the Asiatic subspecies are characterized by sparser manes than average African lions.
Maneless lions have been reported in Senegal and Tsavo East National Park in Kenya, and the original male white lion from Timbavati was also maneless. Castrated lions have minimal manes. The lack of a mane is found in inbred lion populations; inbreeding also results in poor fertility.
Cave paintings of extinct European cave lions exclusively show animals with no mane or, just the hint of a mane, suggesting to some that they were more or less maneless, however, the females hunting for a pride are more likely the subjects of the drawings—since they are shown in a group related to hunting—so these images are not reliable to make a judgment about whether the males had manes. The drawings do suggest that the extinct species used the same social orginazation and hunting strategies as contemporary prides.
http://en.wikipedia.org/wiki/African_lion