Last names are handy for more than constructing family trees—they can also trace population connections and movements across and between countries. Researchers in China recently mapped the country's so-called isonymy structure, which shows how likely people are to share their last name with those around them. The resulting patchwork matches patterns of ethnic distribution and tracks some of China's historic migrations, such as the diversity of people who settled in the Yangtze River basin over many centuries. Such basic surname calculations, the authors say, can offer quick insight into cultural dispersal in the world's most populous country.
Surnames can act as stand-ins for genetic markers that fathers pass to their children. Like genes, family names are subject to random drift: Over time, certain names become more prevalent than others purely by chance. A region with high surname similarity indicates that a stable population has inhabited the area long enough for drift to take place. A region of low surname similarity suggests the migration of different groups of people into the area.
Although researchers have studied surname structure to deduce the relatedness and movement of populations in a number of other countries, China's family names possess some unique features. The country's recorded history of surnames stretches back 4000 years, and Confucian traditions dictated that surnames were consistently passed through the paternal line without hyphenation or other changes. This stability provides a rare opportunity to study the effects of drift over a long period of time.
Furthermore, the total number of family names in China is staggeringly small. The 1.28 billion people included in the new study shared a mere 7327 surnames (compared with nearly 900,000 last names documented in a study of 18 million people in the United States). This name pool is limited partly because Chinese surnames traditionally consist of a single character. Another factor is that about 85% of the population shares the 100 most common surnames and one-fifth of Chinese people have the surnames Wang, Li, or Zhang.
Systems scientists at Beijing Normal University in China, who study relationships within complex networks, wanted to determine if they could spot patterns among the surnames of a sample of 1.28 billion people listed by China's National Citizen Identity Information Center. They calculated the likelihood that people shared a surname within a given region and then compared how similar the regions were to one another. They then made these comparisons on three geographic scales, which included 30 large provinces, 334 midsized prefectures, and 2811 counties. Finally, they drew on historical records for possible explanations of the patterns they observed.
When the researchers mapped their data, a few major features popped out. Many regions with a high prevalence of shared surnames also contained large populations of ethnic minorities, the team will report in an upcoming issue of the American Journal of Physical Anthropology. These regions in far western and southern China were also dissimilar from the rest of the country. This may reflect the fact that ethnic minorities often have unique surnames and tend to marry within their groups, the authors say.
The similarity in surnames between two locations tended to decrease as the distance between the locations increased. This "isolation by distance" is a hallmark of drift happening over a long period of stable habitation. However, the researchers also found evidence of migration's influence. The counties along either side of the lower Yangtze River exhibit very low surname similarity. This diversity is perhaps due to the many large-scale migrations to this region over China's history, the authors say. In addition, the very high surname similarity between the eastern province of Shandong and a cluster of provinces in the northeast of China may reflect the migration of more than 20 million people from Shandong to the northeast in the 19th and 20th centuries.
"We are surprised that famous large-scale migrations can be shown by such simple calculations," says study co-author Jiawei Chen.
However, the researchers describe just a few of the many migrations that are important to China's history, says Diana Lary, a historian at the University of British Columbia, Vancouver. Lary cautions that surname patterns are a simplified way of looking at stories of migration. "There's usually a specific reason why some places have very high numbers of migrants and others don't," she says. "People were relocated by the government, or were famine migrants, or refugees from various kinds of turmoil."
The study's findings add to an increasingly global perspective of surname distribution, says Malcolm Smith, an anthropologist at Durham University in the United Kingdom. He says that the paper provides a starting point to address additional questions. "You can look at a whole suite of things that are going on in China—genetic variation, linguistic variation, cultural traditions—and see the extent to which that is consistent with surname variation."
Just like all the Smiths in the United States are not related to each other, shared surnames in China do not necessarily reflect common ancestry. However, Chen says Chinese surnames still contain some genetic information, and as a next step his colleagues plan to investigate whether the country's mosaic of surnames matches up with genetic diversity.