The trade-off between symmetry and asymmetry

Population-level asymmetry may be maintained, not by an "evolutionarily stable strategy" pitting a dominant bias against its nondominant opposite, but rather by a genetically based system pitting a directional bias against the absence of any such bias. Stability is then achieved through a heterozygotic advantage, maintaining balanced polymorphism. This model may better capture the fundamental trade-off between lateralization and bilateral symmetry.