After the 16th century, the colonial period saw the influx of genetic influence from other populations. This is evidenced by the presence of a small percentage of the Y-DNA Haplogroup R1b present among the population of the Philippines. DNA studies vary as to how small these lineages are. A year 2001 study conducted by Stanford University Asia-Pacific Research Center stated that only 3.6% of the Philippine population had European Y-DNA. According to another genetic study done by the University of California San Francisco, they discovered that a more "modest" amount of European genetic ancestry was found among some respondents who self-identified as Filipinos. Practicing forensic anthropology, while exhuming cranial bones in several Philippine cemeteries, researcher Matthew C. Go estimated that circa 6% of the mean amount, among the samples exhumed, have attribution to European descent. According to a genetic study written by Maxmilian Larena, published in the Proceedings of the National Academy of Sciences of the United States, the Philippine ethnic groups with the highest amounts of Spanish/European descent are the Bicolanos, with 2 out of 10 Bicolanos being Spanish, and Chavacanos, with 4 out of 10 Chavacanos being of Spanish descent. Other lowland urbanized Christian Filipino ethnic groups also show European descent.