What constitutes a Chinese?
First and foremost, I need to emphasize that once again (and it’s the fact): Chinese is a not a single race. Chinese is a a sense of belonging for all the people that live under the influence of Chinese culture and develop (either voluntarily or involuntarily) their identity and affiliation to Chinese civilization, such as adopting Classic Chinese language, adjusting into Chinese agricultural societal order, converting into Chinese philosophy, recognizing the orthodox Chinese historiography, and using Chinese naming system etc. In the Chinese history, there were innumerable counts that northern Turkic/Mongolic/Tungusic/Tocharian nomads invaded the agriculture-based China and gradually submerged in the widening gene pool of modern Chinese population (mostly between Mongoloid nomads and Chinese, e.g. Turkic, Mongolic, and Tungusic; Tocharian influx is very limited), as well as southern Hmong-Mien/Tai-Kadai tribes that integrated the Northern Chinese settlers and became sinicized over the time. Basically Chinese agricultural civilization is like an super vortex that kept on engulfing its neighboring steppe riders and forest dwellers. The China Proper today is a direct result of Chinese culture expansion up to late 19th century and early 20th century (from both cultural assimilation and Han Chinese immigration). Countries like Korea and Vietnam would be rather difficult to strive for independence if they did not struggle out of sinosphere – their artificially-made written script plays a vital role in keeping their original identity from the gradual sinificiation process.
On the same time, it is rare in the history that Chinese expanded China proper through successful military campaigns. As a matter of fact, after Anshi rebellion in mid-Tang dynasty, or around 750AD, China had always been passive in dealing with the nomads. China proper even started to be at the hands of steppe riders completely by the Mongols in 1279AD and later by Manchus in 1644AD (while Northern China proper briefly under Nomad’s control in Wu Hu era (304AD-439AD) before Anshi rebellion and Ming dynasty (1368AD-1644AD) be the only effective Chinese central government’s control on Northern China Proper after the Tang dynasty). However, the expansion of China proper (Chinese culture) went even further and more swiftly after the influx of nomads in Northern China and outflux of Chinese in the Southern “savage land”.
To explain the extremely elastic vitality of Chinese culture before the arrival of Western influence (communism being the ultimate terminator of classic Chinese culture), I always like to compare Chinese culture to the expansion of Christianity in Europe. Those two share a lot of similarities. They both hold a holistic and coherent worldview and social codes to help maintain an agricultural-centric society; they both highly adopted by the ruling class as a sense of identity to increase the centripetal force among all social classes; and they both expand outwards while outer culturally inferior tribes were militarily superior and invading inwards. The only difference is that while Christianity was more proactive in converting nomadic tribes and forest hunters in the name of religion, which emphasizing more on the recognition of its religious worldview and less on the assimilation of culture and language (Christianity being the major force in creating the written script for many European languages and thus preserving their own ethnic/cultural identities in Europe); Chinese never proactively preached non-Chinese, instead it was largely those nomads and tribes that have got in contact with the Chinese consciously decided to fully assimilate into Chinese, therefore taking up the whole package of Chinese philosophy (language, history, worldview etc.) and developing into the defenders of Chinese culture (the most notable case being the sinification process of Emperor Xiaowen of Northern Wei in late 400AD).
The reason behind the strong magnetic effect of Chinese culture is quite straightforward: Chinese civilization (especially Confucianism) provides a stable social order for the agriculture-based regime, and thus a much easier livelihood for steppe nomads and southern mountainous tribes. Chinese culture superiority in East Asia was thus based on its complementary agricultural ethics and technology as well as the enormous luxury it produced. Who would rather go to hunt in the mountains and herd sheep while they realize could just make food out of agriculture? Classic Chinese therefore became to Lingua-Franca in the whole East Asia.
As a result, many Northern Chinese would probably carry more blood of Hu (Chinese term for all northern nomads) and many Southern Chinese with Man (Chinese term for all Southern tribes) blood. Interestingly, at certain point there were even speculations that a Chinese village in Northwestern China might have lived the descendants of the missing Roman legion after the Battle of Carrhae in 53BC. Though this proved falsified later, DNA test did confirm a significant contribution of Caucasian gene in the village (probably more likely as a result of Persian-Sogdian influx). All of these point to the fact that the identity of being a Chinese is rather a sense of cultural identification than a result of kinship expansion. And Classic Chinese culture (which is a result of thousands of years’ gradual assimilation of all agricultural breeds in the Yellow River basin until 221BC) played a vital role in connecting different breeds into the China proper.
However, Classic Chinese culture experienced drastic downfall since the May-fourth Movement in 1919. The traditional Sino-centric worldview has bee fiercely attacked by Chinese intellectuals who viewed Classic Chinese as the dead-weight that held back China modernization. A wave of aggressive anti-classicism movement surged at that time. At that time someone even proposed to totally abandon Chinese script, one of the three independently developed written script (the one being Sumerian cuneiform and Egyptian hieroglyph) and the only one that has been continuously developed and used ever since, to adopt a total romanization of Chinese language. Though this was even seen extreme at that time, classic Chinese was gradually downplayed in the Chinese education ever since. Vernacular Chinese, a colloquial interpretation of Northern Mandarin Chinese dialect, was promoted nationwide as the standard Chinese ever since. Without the support of Classic Chinese, the cultural identity of Chinese significantly declined. Instead, the modern nationalism stepped in and replaced Chinese culture as the main source of Chinese identity afterwards. Chinese Classicism was later put into an end after the takeover of the extreme left-wing communist regime after 1949, especially after the introduction of the modern ethnic definition in China and the Cultural Revolution. Nowadays, alas, Chinese Classic culture becomes merely an exclusive possession of a very few number of Chinese intellectuals like me, who could only find a sense of comfort and admiration in the past while looking at the contemporary desinicizing China.
What constitutes a Chinese? As much as I am aware of every logic reasoning in this question, I still firmly believe a proper Chinese could have a full understanding and appreciation of Classic Chinese culture and language. Just because you happen to have genes that give you Mongoloid facial feature and speak vernacular Chinese (or even don’t know how to speak among some overseas Chinese), doesn’t mean you are qualified as a Chinese (Starting calling yourself Asians, good for both of us). As a Chinese Classicist I found it quite hard to obtain a sense of belonging in the modern China (ill-manner, money-worshiping, dishonesty are never classic Chinese!). Classic China is all I could relate to. If you want to be a real Chinese, act like a proper Chinese. 君子明春秋大義也！