The origin of the Thai people is not clear. The Thai people have characteristic features that are different than that of Vietnamese or most Chinese. There are about three or four Thai ethnic sub-races as can be determined by facial features and skin tones. Those in Isan, for example, look like Cambodians, and many in Northern Thailand look like Burmese. Many think that some of the Thai ancestors came from the region of southern China. Some people think that some of the Thai ancestors came from central China around the Yangtze River. The Thai language is a tonal language, but linguists haven't found a link between the linguistic family group of the Thai language and other tonal language groups such as that in central China. This doesn't necessarily mean that some of the Thai ancestors didn't come from central China because perhaps they adopted the Thai regional language. The Thai people are probably mainly a mixture of people from around southern China and Southeast Asia.