The mane on a male lion serves as ornamentation, akin to the beautiful iridescent feathers on a male peacock, and it is used to attract attention from lionesses and to intimidate competing males. The quality and color of the mane also signal a particular lion's overall health and fitness.
A long, black mane is the most desirable to lionesses and the most intimidating to male rivals. However, scientists speculate that increasing global temperatures may introduce considerable heat stress on lions possessing this otherwise desirable physical trait. Consequently, as of 2014, male lions--particularly those that possess the long, black mane--may lose their manes altogether in the coming years if global temperatures continue to increase.