Yesterday, Scientific American released a short essay by Michael Shermer, “Did This Extinct Human Species Commit Homicide?”. Shermer is a regular columnist and contributing editor of Scientific American and the editor of Skeptic magazine. He is widely recognized as a leader of the skeptic movement in the U.S.
Here’s a sentence summing up his idea of a violent fate for Homo naledi:
Whatever you call it—war or murder—it is violent death nonetheless, and further examination of the Homo naledi fossils should consider violence (war or murder for the adults, sacrifice for the juveniles) as a plausible cause of death and deposition in the cave.
“War or murder for the adults, sacrifice for the juveniles.” Shermer conjures the Dinaledi Chamber in the bowels of an Aztec pyramid.
It doesn’t sound like the work of a skeptic. Shermer does not seem to have read our open access paper very carefully, because he seems completely oblivious to the evidence most relevant to his idea.
Kids thinking like scientists
Just before heading off for our holiday trip to Kansas, I made a special trip to my son Goodwin’s 4/5 classroom at New Century School. The teachers had booked me for a 45-minute session talking about Homo naledi with around forty 9-year-olds and 10-year-olds.
I had a great time with the kids. I brought around twenty 3D prints of Homo naledi bones, and they made quick work identifying them. The kids and teachers were fascinated to learn more about the cavers and archaeologists who were part of the underground team. After the 45 minutes were up, many of the kids showed no shortage of questions, and twenty of them stayed on for another 45-minute period to ask more.
There was one thing that occupied their imaginations more than anything else: How did those bodies get into the Dinaledi Chamber?
All respect to Carl Sagan, but he was wrong when he wrote, “Every kid starts out as a natural-born scientist, and then we beat it out of them.” I’ve spent a lot of time doing science outreach for kids of all ages. Scientists and children look at evidence very differently.
A kid looks at a problem by inventing the story that may lead to the problem. The kids in Goodwin’s class thought of no end of stories that could lead to bodies being found in the Dinaledi Chamber.
“What if they were running from a lion and they hid in the cave, but they got trapped there and couldn’t find their way back out?”
“What if they were sick and their friends put them there like a quarantine?”
“What if another group killed them in a ritual and hid the bodies there?”
“What if they were really scared of lightning and went deep underground to be safe, but got stuck there?”
“What if it was a jail for the bad people and they died there?”
“What if they were living in some other part of the cave, and this was where they put them when they died?”
“What if there was an earthquake, and it trapped them in the cave?
“What if they were some kind of human sacrifice?”
“What if they were zombies and people locked them down underground?”
They came up with a hundred variations on stories that could end up with bodies in a deep underground chamber.
I explained that these were all very imaginative ideas, and imagination is an important part of scientific thinking. But there is more. A scientist looks at a problem by considering how to gather evidence to test hypotheses. One important part of science is recognizing that a story can be broken down into parts that can be tested with evidence.
The kids then thought of several ways to test some of their ideas, and I helped answer questions by pointing to the evidence in our research papers.
Why kids are better scientists than Michael Shermer
Now obviously Goodwin’s classmates don’t write for Scientific American, but you’ll recognize Shermer’s murder-sacrifice idea is very much the same as one of the kids’ ideas.
When I challenged the kids to think of how to test this murder hypothesis, they came up with an answer that would make a forensic anthropologist proud: Look at the bones for signs of violence. And I could tell them, that’s exactly what we did in our research paper (Dirks et al. 2015)!
We undertook a detailed taphonomic study of the surfaces and fracture patterns of the collection, led by Lucinda Backwell who is a world expert in the trace analysis of fossil remains. The bone in the collection is highly fractured and fragmented, but all of those fractures are consistent with breakage from static loading from sediment in the Dinaledi chamber. No fractures are indicative of a fresh, “green” fracture at or near the time of death. None of the bone fragments have traces of cutmarks or tooth marks that would result from butchery, disarticulation, percussion, or consumption of the remains. There are no cranial bone fragments with radiating fracture lines or signs of intentional breakage. In other words, none of the bone shows any traces that indicate that the individuals met a violent end.
This is the simple answer to Shermer’s question, already available in our open access paper. The bones bear no trace of violence. So how did Shermer miss this evidence?
Storytelling and skepticism
The schoolkids understood right away that the idea of murder and sacrifice don’t match the evidence that we have so far. Shermer preferred to speculate without evidence and publish an essay without fact-checking.
It doesn’t seem like the work of a skeptic.
He concludes his essay:
It's a side of our nature we are reluctant to admit, but consider it we must when confronted with dead bodies in dark places.
The kids in Goodwin’s class were not at all reluctant to talk about dead bodies in dark places. Their imaginations turned immediately to murder and sacrifice, jails and quarantines. Their ideas reflect their cultural background and education, not the world of Homo naledi. “Jail” is not a concept that would be familiar to non-human primates. Neither is “burial”. Or “quarantine”. Or “sacrifice”. A skeptic must recognize these cultural assumptions and biases so that she can look beyond them.
Shermer’s essay displays some of his own assumptions and background. He has written a great deal about the dark side of human nature, including his recent book, The Moral Arc: How Science Makes Us Better People. He thinks about ancient people through the lens of moral progress. He has read extensively about the archaeology of violence and warfare among recent humans. He expresses disdain about our team’s decision to publish in open access journal instead of “prestigious journals” like Nature or Science. He assumes that our team has not “meticulously sorted through the 1550 fossils” because we haven’t spent “many years” describing them.
That last one especially irks me, since “meticulously sorting through the 1550 fossils” has basically been my job description for the past two years.
Any skeptic can tell you that a common rhetorical trick is to pack a story full of details that seem to corroborate each other, usually details that satisfy the reader’s pre-existing assumptions and biases. Shermer’s essay gives us some interesting details about violence in the past. But he has ignored the Dinaledi evidence entirely.
Shermer should think like a skeptic. Irrelevant details do not strengthen a story or make it more credible. Logic tells us that a story must be less probable than the least probable of its parts.
Look closely at Shermer’s story: Homo naledi murdered some adults and ritually sacrificed some children, and then deliberately deposited the bodies into the Dinaledi Chamber. This uses a logical “AND” to combine the hypothesis of deliberate deposition with the hypothesis of murder and sacrifice. To Shermer murder and sacrifice seem probable, possibly because they seem to supply Homo naledi with a motive to deposit bodies in a remote chamber. But a skeptic should have taken note of that logical “AND”. There are many possible reasons why bodies might have been deposited in the Dinaledi Chamber, murder and sacrifice are only one such hypothesis, and the evidence presently stands against them.
Obviously, we cannot predict the future. We may someday uncover evidence to establish a violent cause of death for one or more of the bodies. We cannot predict what we may find in future excavation of the Dinaledi Chamber. We should keep an open mind.
But Shermer is wrong to ignore the evidence that already exists. The editor of Skeptic magazine failed to do the one thing that any journalist should do: simply ask someone whether he was missing some important evidence that might make him look like a fool. I’m very sorry that he has misled so many Scientific American readers about the nature of evidence about Homo naledi and how we approach the science of human origins.
Berger, L. R., Hawks, J., de Ruiter, D. J., Churchill, S. E., Schmid, P., Delezene, L. K., ... & Zipfel, B. (2015). Homo naledi, a new species of the genus Homo from the Dinaledi Chamber, South Africa. eLife, 4, e09560. doi:10.7554/eLife.09560
Dirks, P. H., Berger, L. R., Roberts, E. M., Kramers, J. D., Hawks, J., Randolph-Quinney, P. S., ... & Tucker, S. (2015). Geological and taphonomic context for the new hominin species Homo naledi from the Dinaledi Chamber, South Africa. eLife, 4, e09561. doi:10.7554/eLife.09561