Lions are definitely not loners. In fact, lions are unique among felids in that they are the only species of cat that forms social groups. All other cats are solitary hunters that, outside of mating season, shy away from others of their kind.
The two social groups that shape the lives of lions are prides and coalitions. A pride is a group of 1 to 18 female lions and their young. A coalition is a group of 1 to 9 male lions.
A coalition of males competes with other male coalitions for exclusive access to a pride of females. A coalition that wins a pride remains associated with the pride for a period of about 3 to 4 years. After that time, challenges from other coalitions of nomadic males often prevail and the resident coalition is displaced.
When one coalition ousts another from its place within a pride, the consequences are fatal for any unweaned cubs sired by the previous coalition's males. The incoming coalition males kill the cubs and evict any subadult males from the pride. Adult females are thus hastened to return to estrous and mate with the new males.
Within the pride-coalition group, males compete with one another to form pairs with females. Once all males have paired off with females, they prevents other males from mating with their mate. But often there are more females than there are males and the unpaired females choose among the males as mates. In this case, unpaired females often prefer darker-maned males, as they are more likely to have greater vitality, fighting prowess and social status than their lighter-maned counterparts.
Kingdon J. 2007. The Kingdon Field Guide to African Mammals. Harcourt Brace & Company. New York, NY. 464 p.