The adoption of Cao Cao’s father, Cao Song, was common knowledge. But in ancient times, there was no way to prove that Cao Song had been adopted from within his own clan, or to disprove that he was adopted from beggardom as Cao Cao’s opponents claimed. Nowadays with complex genetic analyses we have the ability to answer this and many other questions of heritage and ancestry.
Cao Cao rose to power in the final years of the Eastern Han Dynasty in the early 3rd century. He was a cruel and merciless warlord, but also a brilliant ruler and a military genius.
He is described in literature as a leader “able enough to rule the world, but evil enough to destroy it.” He was posthumously honored as “Emperor Wu de Wei,” since he played such a central role in establishing the foundation for what was to become the state of Cao Wei in the Three Kingdom period.
Cao Cao claimed to be a descendant of Marquis Cao Can and therefore of aristocratic ancestry. However, this claim has been questioned for around 1800 years. There is also suspicion that his father Cao Song had been adopted from beggardom, putting more of a question on Cao Cao’s right to rule.
Was Cao Song adopted, by the eunuch Cao Teng, from within his own family clan (a common practice at the time)? Or did Cao Teng choose a child from beggardom?
Testing the claim to aristocratic ancestry
In 2012, scientists set out to use genetic analyses to test the claim the emperor descended from Marquis Cao Can. They obtained Y-DNA profiles from clans that claim to be descendants of Cao Cao or Cao Can (with records available to prove their ancestry for at least 70-100 generations).
Y-DNA is passed down from father to son along the direct paternal lineage. So all males who have descended from the same paternal lineage are expected to have exactly the same or very similar Y-DNA profiles.
Two different types of Y-DNA markers are used to trace ancestry: fast changing STRs (short tandem repeats) and slow changing SNPs (single nucleotide polymorphisms). In this case, researchers used Y-DNA STRs to map the descendants of Cao Cao and Cao Can to the Y chromosome evolutionary tree.
An evolutionary tree is like a family tree, showing all the different family groups. The major branches of the tree are called haplogroups identified by letters (A to T). Haplogroups can be thought of as ancient family groups that existed thousands of years ago.
If they are related, the Y-DNA profiles of clans that claim to be descendants of either the Emperor or the Marquis would belong to the same haplogroup. However, this was not the case.
Descendants of Cao Cao belonged to the Y-DNA haplogroup O2*, while he Marquis Cao Can’s descendants belonged to the haplogroup O3*. Genetic evidence therefore didn’t support Cao Cao’s claim that he descended from Cao Can.
Can Song’s adoption
With Cao Cao’s haologroup mapped out, it was possible to tackle an 1800-year-old debate about Cao Song’s (Cao Cao’s father) ancestry. If Cao Song was adopted from within his own clan, as claimed by the emperor, Cao Cao should share the same Y-DNA profile as his paternal granduncle, Cao Ding.
A partial Y-DNA STR profile was obtained from a tooth from the tomb of Cao Ding to test this hypothesis. This partial profile matched closely to the Y-DNA haplogroup O2* – the same haplogroup as Cao Cao’s descendants.
This means DNA evidence corroborates the historical documents. Cao Song was indeed adopted from within his own clan, possibly the son of a brother or a paternal uncle of Cao Teng.
These studies have defined the presumed Y-DNA STR paternal line profile of Emperor Cao Cao from modern clans that proclaim to be his descendants. If you have taken the DNA Paternal Ancestry Test, you can compare your DNA against Emperor Cao Cao to see if you have descended from the same Cao clan.
Wang C et al. (2013) Ancient DNA of Emperor CAO Cao’s granduncle matches those of his present descendants: a commentary on present Y chromosomes reveal the ancestry of Emperor CAO Cao of 1800 years ago. J Hum Genet. 58:238-239.