During the four millennia that saw the rise to power of states in western Asia and in Egypt, East Asia followed a unique trajectory, though – very early on – contacts led to the introduction of techniques and products from the west. China, where sedentary communities developed, was a primary center for the domestication of plants and animals. The Neolithic communities in the Yangtze valley region developed slightly later than in western Asia, possibly practicing agriculture during the eighth millennium bce (but more likely during the sixth); a process of rice domestication subsequently began, which led to the development of japonica varieties in the east (though it would be more correct to speak of sinica) and – for some authors – of indica types further south and west.