This may be related to their way of life.
Unlike other members of the cat family, lions live in prides — groups consisting of one male, several females, and offspring of various ages.
Members of the pride regularly interact with each other, not limited to just the mating season. In such a social structure, signals are important, which help regulate aggression, including allowing the determination of a clan member's sex from a distance.
The mane, which is a characteristic feature of adult males, serves precisely this function.
