Phenotypic variations in a population can be influenced by neutral drift and threshold selection. In a study on antibiotic resistance, researchers found that under low antibiotic levels, neutral drift can lead to significant variation in resistance strength. They discovered that high-resistance variants can emerge without adaptation, due to a combination of mutation-selection balance and a threshold-like relationship between fitness and phenotype. This explains why genes in nature often exhibit phenotypic variation, contributing to population-level evolvability.