Why do lions have manes?
Executive summary
Lions’ manes are best understood as a multifunctional trait shaped by sexual selection, male–male competition and environmental trade‑offs: manes signal male quality to females and rivals, can protect the neck during fights, but impose costs in hot climates that limit their expression [1] [2] [3]. Empirical work — from field observations and experimental models to regional comparisons — supports a composite explanation rather than a single cause [1] [4] [2].
1. The competing origin stories: protection vs. signal
Two long-standing hypotheses explain why male lions evolved manes: Darwin’s idea that the mane provides physical protection in fights, and the sexual‑selection hypothesis that manes evolved as conspicuous signals of male quality to mates and rivals; scientists have treated these as complementary, not mutually exclusive, pathways [5] [1] [6].
2. Sexual selection: mane color and size as honest signals
Field experiments and long‑term studies show that darker, fuller manes correlate with attractiveness to females and with perceived threat by other males — females prefer darker manes and males avoid longer, darker‑maned rivals — indicating manes function as sexual and dominance signals that increase reproductive success [1] [4] [3].
3. Protection and intimidation in male–male contests
Observational and theoretical work supports the protective and intimidating roles of the mane: the hair around the head and neck can cushion bites and make a male appear larger, reducing the likelihood of lethal injury and deterring challengers, which matters in intense pride takeover and territorial fights [7] [8] [9].
4. Costs: heat, fertility and ecological trade‑offs
Manes carry measurable costs in hot environments — heavily maned males overheat more readily and can suffer downstream effects on sperm production and feeding — explaining why populations in warmer, more humid regions often show reduced or lighter manes; this trade‑off illustrates natural selection constraining sexually selected traits [2] [3] [5].
5. Variation: genes, hormones and environment
Mane development is influenced by testosterone and genetics, but temperature and condition also shape expression: testosterone drives mane growth yet similar hormone levels don’t fully predict mane size, and studies link colder climates to fuller manes while nutrition and injury influence individual variation, indicating a multilayered developmental basis [10] [4] [1].
6. Evidence, experiments and the limits of certainty
Rigorous approaches — toy‑lion experiments that revealed male avoidance of long manes and female preference for darker manes, plus longitudinal field data — give strong empirical weight to signaling hypotheses, while comparative regional data bolster the climate‑cost argument; however, not every pattern is universal and some sources (for example creationist interpretations) frame the trait through non‑evolutionary lenses that carry explicit ideological agendas and are not consistent with mainstream empirical work [1] [11] [10].
7. Bottom line: a multifunctional, context‑dependent crown
The mane is an evolved, male‑specific trait that functions primarily as a signal of fighting ability and reproductive quality while providing secondary protection in fights; its expression reflects a balance between sexual advantage and ecological cost, producing the geographic and individual variation observed across lion populations [6] [3] [2].