The species has been isolated by a variety of mechanisms including behavioural differences and genic incompatibility but hybridization is not unknown. Some phylogenetic studies of junglefowl show that this species is more closely related to the Sri Lankan junglefowl "Gallus lafayetii" than to the red junglefowl, "Gallus gallus", but another study shows a more ambiguous position due to hybridization. However, the time of divergence between the grey junglefowl and Sri Lankan junglefowl around 1.8 million years ago is more recent than 2.6 million years ago calculated for between the grey junglefowl and red junglefowl. This divergence time support sister relationship between grey junglefowl and Sri Lankan junglefowl.