The Sino-Austronesian hypothesis, on the other hand, is a relatively new hypothesis by Laurent Sagart, first proposed in 1990. It argues for a north–south linguistic genetic relationship between Chinese and Austronesian. This is based on sound correspondences in the basic vocabulary and morphological parallels. Sagart places special significance in shared vocabulary on cereal crops, citing them as evidence of shared linguistic origin. However, this has largely been rejected by other linguists. The sound correspondences between Old Chinese and Proto-Austronesian can also be explained as a result of the Longshan interaction sphere, when pre-Austronesians from the Yangtze region came into regular contact with Proto-Sinitic speakers in the Shandong Peninsula at around the 4th to 3rd millennia BCE. This corresponded with the widespread introduction of rice cultivation to Proto-Sinitic speakers and conversely, millet cultivation to Pre-Austronesians. An Austronesian substratum in formerly Austronesian territories that have been Sinicized after the Iron Age Han expansion is also another explanation for the correspondences that do not require a genetic relationship.