In 2012 during excavation for a shopping mall near San Francisco, a mass grave containing 7 men was unearthed. The manner in which they were buried led archaeologists to believe that they had been murdered, and quickly buried, not ceremonially buried as tribal members would be. They were found among more than 200 other burials.
The victims ages ranged from about 18 to about 40 and scientists concentrated on analyzing the wounds, cause of death and DNA of these men. In part, they wanted to see if they were related to each other and if they originated in this area or came from elsewhere. In other words, were they unsuccessful invaders as suggested by the circumstances of their burials?
This article tells more about the excavations and includes some photos.
Analysis suggests the men lived about 1200 years ago, clearly before European contact. Analysis of the men’s teeth provided information about their history. These men had spent their lives together, but their isotope signatures were clearly different than the individuals in the balance of the burials. Indeed, they look to have been invaders.
An academic paper titled “Isotopic and genetic analysis of a mass grave in central California: Implications for precontact hunter-gatherer warfare” was published a few weeks ago in the American Journal of Physical Anthropology. The article itself is behind a paywall available here. The abstract is provided below:
Analysis of a mass burial of seven males at CA-ALA-554, a prehistoric site in the Amador Valley, CA, was undertaken to determine if the individuals were “locals” or “non-locals,” and how they were genetically related to one another.
The study includes osteological, genetic (mtDNA), and stable (C, N, O, S) and radiogenic (Sr) isotope analyses of bone and tooth (first and third molars) samples.
Isotopes in first molars, third molars, and bone show they spent the majority of their lives living together. They are not locals to the Amador Valley, but were recently living to the east in the San Joaquin Valley, suggesting intergroup warfare as the cause of death. The men were not maternally related, but represent at least four different matrilines. The men also changed residence as a group between age 16 and adult years.
Isotope data suggest intergroup warfare accounts for the mass burial. Genetic data suggest the raiding party included sets of unrelated men, perhaps from different households. Generalizing from this case and others like it, we hypothesize that competition over territory was a major factor behind ancient warfare in Central California. We present a testable model of demographic expansion, wherein villages in high-population-density areas frequently fissioned, with groups of individuals moving to lower-population-density areas to establish new villages. This model is consistent with previous models of linguistic expansion. Am J Phys Anthropol, 2015. © 2015 Wiley Periodicals, Inc.
I was extremely disappointed with the genetic information. Working with the local Ohlone community, the scientists did attempt to extract DNA from the 7 individuals in the mass grave, with 6 extractions being successful.
They only analyzed the HVR1 region of the mitochondrial DNA.
In the paper, the authors indicate that nuclear DNA which would include the Y chromosome as well as autosomal DNA was too degraded to recover. While disappointing, there is nothing they can do about that.
However, only analyzing the mitochondrial DNA, which they clearly were able to amplify, at the HVR1 level is an incredible lost opportunity. They obtained enough resolution in 6 of the individuals to obtain general haplogroup assignments. However, the HVR2 and coding regions would have provided the defining information about extended haplogroups and individual mutations, including, perhaps, haplogroups never seen previously in the Americas.
Furthermore, given the information above, we can’t tell if the D1 individuals are related to each other matrilineally or not. The B2 individuals are clearly not related in a recent timeframe nor are the A2, B2 and D1 people related to each other on their matrilineal line. What a shame more information wasn’t obtained.
While I’m grateful that DNA testing was undertaken, I’m saddened by the partial results, especially in this day of full genomic sequencing for ancient DNA specimens. I’m perplexed as to why they would not have obtained as much information as was possible, given the significant effort expended in recovering any ancient DNA specimen.
How do they know that the men with different genetic profiles were victim of a boat wreck or natural disaster?