Is introversion genetic?

Twin studies put the heritability of extraversion-introversion at roughly 40 to 60%, among the highest for personality traits. Most of the remaining variance is 'non-shared environment', the experiences that differ even between siblings in the same home; shared family environment contributes little. Identical twins raised apart score far more alike than fraternal twins.

Source: Bouchard & McGue (2003), Journal of Neurobiology; Vukasović & Bratko (2015), Psychological Bulletin