Ancient Humans: Violent? Caring?

A report in the November 21 issue of PNAS opens a sobering window into the lives and deaths of Ice Age humans. The report analyses a skull found in China and dating to 126,000 years ago and showing clear evidence of blunt force trauma.

[See photo, left. This is the right superolateral view of the Maba cranium showing the position (A) and detail (B) of the depressed lesion. Credit: University of the Witwatersrand.]

Was it aggression or an accident, deliberate violence or just an sharp but unlucky bump to the head? No one knows for sure. Based on comparison with similar findings, however, researchers suspect human-to-human violence.

One thing that makes this discovery stand out is its early date. Quite possibly, it is the earliest known evidence of human aggression against another human being.

The injury was not fatal. The trauma to the skull shows clear evidence of healing. For researchers, this healing is proof that the victim lived months and possibly years after the injury, quite possibly because of care offered by fellow Middle Pleistocene humans. If true, then the skull may be evidence of human caring as well as human violence.

According to Prof. Lynne Scheparz, one of the authors of the study, “this wound is very similar to what is observed today when someone is struck forcibly with a heavy blunt object. As such it joins a small sample of Ice Age humans with probable evidence of humanly induced trauma, and could possibly be the oldest example of interhuman aggression and human induced trauma documented.”

At the same time, the skull’s “remodelled, healed condition also indicates the survival of a serious brain injury, a circumstance that is increasingly documented for archaic and modern Homo through the Pleistocene,” according to Schepartz. In other words, this skull is not unusual in suggesting that ancient humans cared for each other after serious brain injury. As Schepartz puts it in a press release from the University of Witwatersrand, this individual “would have needed social support and help in terms of care and feeding to recover from this wound."

According to the report itself, “the lesion…appears most likely to have been the result of a localized, blunt force trauma, sufficiently strong to produce the concentric ridges, the external depression, and the internal bulge. At the same time, the bone was extensively remodeled…Such remodeling minimally takes several months to develop,” possibly longer.

According to the report, it “is probable that it [the injury] was the result of an interpersonal altercation, with blunt-force trauma, given its form, but accidental injury cannot be excluded. It may be the oldest such case known…”

The report provides a sobering picture of the past. A single skull provides what might be the oldest snapshot of human violence and human caring, a scant 14mm in length but a powerfully accurate view of the best and the worst in us.

The report, “New evidence of interhuman aggression and human induced trauma 126,000 years ago, was published in the November 21, 2011 issue of PNAS.

Complicating the Family Tree

Our view of our past keeps getting more complicated. Our family tree, it turns out, is more of a twisted vine than a neatly linear branch.

Evidence keeps building by the day that our anatomically modern human (AMH) ancestors interbred with earlier forms of “archaic” humans. In the 31 Oct 2011 early online issue of PNAS, Pontus Skoglund and Mattias Jakobsson present evidence for the view that the genetic legacy of the Denisovans is wider than ever thought before.

First is was the Neandertals. This branch of the human family diverged from our own somewhere around 500,000 years ago. Somewhere between 100,000 and just 50,000 years ago, however, AMHs and Neandertals interbred successfully. The result lives on today in our genes. For many of us, our DNA is 2-3% from our Neanderthal ancestors. The Neandertals may be extinct, but their DNA lives on in every cell in the human body.

Then it was the Denisovans, a recently discovered branch of the human family more closely related to Neandertals than to us. What about AMH-Denisovan iInterbreeding? An international team of researchers led by Svante Pääbo of the Max Planck Institute for Evolutionary Anthropology in Leipzig was able to extract Denisovan DNA from tiny fragments of remains. From the extracts, they reconstructed the Denisovan genome and compared it with the human genome. What they found was clear evidence of interbreeding. Some living human beings—those identified as Melanesians—carry Denisovan genes. That was reported in December 2010.

In September, however, Pääbo was joined by David Reich and Mark Stoneking and other colleagues in reporting that the legacy of Denisovan DNA extends beyond the Melanesians. It’s all over the islands that extend below Southeast Asia, including Australia. Not just Aboriginal Australians but Near Oceanians, Polynesians, Fijians, east Indonesians, and other groups as far as the Philippines are carriers of the Denisovan legacy.

According to this study, the genetic legacy of AMH-Denisovan admixture does not include East Asians. This led the authors to conjecture that there are at least two main waves of AMH migration into southeast Asia. The first wave interbred with Denisovans while the second, apparently, did not.

Their work appeared in the 7 Oct 2011 issue of the American Journal of Human Genetics. Reich discusses these findings in a video. Hint: start at minute 22:30.

But now a study published in the online early edition of the Proceedings of the National Academy of Sciences for the week of 31 Oct 2011 presents evidence that East Asians are also descended in part from the Denisovans. In the paper, the authors (Pontus Skoglund and Mattias Jakobsson) write that “we found a significant affinity between East Asians, particularly Southeast Asians, and the Denisova genome.”

Experts in the field will no doubt debate these findings. Just how widespread is the effect of AMH-Denisovan interbreeding? How widely did AMHs and archaic humans interbreed? To what extent does admixture provide any benefit? Does it shed any light on observable differences between different groups within the human family today?

According to Skoglund and Jakobsson, the “history of anatomically modern and archaic humans might be more complex than previously proposed.”

If our past is more complex than we thought, so is our present. What does it mean to be human? It no longer seems to mean that we are all part of a biological species. Whether we like to call ourselves "anatomically modern humans" (AMHs) or Homo sapiens, we are learning that the very concept of species is becoming unfocused by research. Should we speak of AMH-Denisovan "interbreeding" or "hybridization"? Does it matter? Are we separate species or one slightly-tangled humanity?