As I write this blog post, the 2018–19 NFL season is just underway.
During the course of any NFL season, several key games are decided by a controversial call made by the officials. Nobody wants the officials to determine the outcome of a game, so the NFL has instituted a way for coaches to challenge calls on the field. When a call is challenged, part of the officiating crew looks at a computer tablet on the sidelines—reviewing the game footage from a number of different angles in an attempt to get the call right. After two minutes of reviewing the replays, the senior official makes his way to the middle of the field and announces, “Upon further review, the call on the field . . .”
Recently, a team of anthropologists from Spain and the UK created quite a bit of controversy based on a “call” they made from working in the field. Using a new U-Th dating method, these researchers age-dated the artwork in caves from Iberia. Based on the age of a few of their samples, they concluded that Neanderthals produced cave paintings.1 But new work by three independent research teams challenges the “call” from the field—overturning the conclusion that Neanderthals made art and displayed symbolism like modern humans.
U-Th Dating Method
The new dating method under review measures the age of calcite deposits beneath cave paintings and those formed over the artwork after the paintings were created. As water flows down cave walls, it deposits calcite. When calcite forms, it contains trace amounts of U-238. This isotope decays into Th-230. Normally, detection of such low quantities of the isotopes would require extremely large samples. Researchers discovered that by using accelerator mass spectrometry, they could get by with 10-milligram samples. And by dating the calcite samples with this technique, they produced minimum and maximum ages for the cave paintings.2
Call from the Field: Neanderthals Are Artists
The team applied their dating method to the art found in three cave sites in Iberia (ancient Spain): (1) La Pasiega, which houses paintings of animals, linear signs, claviform signs, and dots; (2) Ardales, which contains about 1,000 paintings of animals, along with dots, discs, lines, geometric shapes, and hand stencils; and (3) Maltravieso, which displays a set of hand stencils and geometric designs. The research team took a total of 53 samples from 25 carbonate formations associated with the cave art in these three cave sites. While most of the samples dated to 40,000 years old or less (which indicates that modern humans were the artists), three measurements produced minimum ages of around 65,000 years, including: (1) red scalariform from La Pasiega, (2) red areas from Ardales, and (3) a hand stencil from Maltravieso. On the basis of the three measurements, the team concluded that the art must have been made by Neanderthals because modern humans had not made their way into Iberia at that time. In other words, Neanderthals made art, just like modern humans did.
Figure: Maltravieso Cave Entrance, Spain. Image credit: Shutterstock
Shortly after the findings were published, I wrote a piece expressing skepticism about this claim for two reasons.
First, I questioned the reliability of the method. Once the calcite deposit forms, the U-Th method will only yield reliable results if none of the U or Th moves in or out of the deposit. Based on the work of researchers from France and the US, it does not appear as if the calcite films are closed systems. The calcite deposits on the cave wall formed because of hydrological activity in the cave. Once a calcite film forms, water will continue to flow over its surface, leeching out U (because U is much more water soluble than Th). By removing U, water flowing over the calcite will make it seem as if the deposit and, hence, the underlying artwork is much older than it actually is.3
Secondly, I expressed concern that the 65,000-year-old dates measured for a few samples are outliers. Of the 53 samples measured, only three gave age-dates of 65,000 years. The remaining samples dated much younger, typically around 40,000 years in age. So why should we give so much credence to three measurements, particularly if we know that the calcite deposits are open systems?
Upon Further Review: Neanderthals Are Not Artists
Within a few months, three separate research groups published papers challenging the reliability of the U-Th method for dating cave art and, along with it, the claim that Neanderthals produced cave art.4 It is not feasible to detail all their concerns in this article, but I will highlight six of the most significant complaints. In several instances, the research teams independently raised the same concerns.
- The U-Th method is unreliable because the calcite deposits are an open system. The concern that I raised was reiterated by two of the research teams for the same reason I expressed. The U-Th dating technique can only yield reliable results if no U or Th moves in or out of the system once the calcite film forms. The continued water flow over the calcite deposits will preferentially leech U from the deposit, making the deposit appear to be older than it is.
- The U-Th method is unreliable because it fails to account for nonradiogenic Th. This isotope would have been present in the source water producing the calcite deposits. As a result, Th would already be present in calcite at the time of formation. This nonradiogenic Th would make the samples appear to be older than they actually are.
- The 65,000-year-old dates for the three measurements from La Pasiega, Ardales, and Maltravieso are likely outliers. Just as I pointed out before, two of the research groups expressed concern that only 3 of the 53 measurements came in at 65,000 years in age. This discrepancy suggests that these dates are outliers, most likely reflecting the fact that the calcite deposits are an open system that formed with Th already present. Yet, the researchers from Spain and the UK who reported these results emphasized the few older dates while downplaying the younger dates.
- Multiple measurements on the same piece of art yielded discordant ages. For example, the researchers made five age-date measurements of the hand stencil at Maltravieso. These dates (66.7 kya [thousand years ago], 55.2 kya, 35.3 kya, 23.1 kys, and 14.7 kya) were all over the place. And yet, the researchers selected the oldest date for the age of the hand stencil, without justification.
- Some of the red “markings” on cave walls that were dated may not be art. Red markings are commonplace on cave walls and can be produced by microorganisms that secrete organic materials or iron oxide deposits. It is possible that some of the markings that were dated were not art at all.
- The method used by the researchers to sample the calcite deposits may have been flawed. One team expressed concern that the sampling technique may have unwittingly produced dates for the cave surface on which the paintings were made rather than the pigments used to make the art itself. If the researchers inadvertently dated the cave surface, it could easily be older than the art.
In light of these many shortcomings, it is questionable if the U-Th method to date cave art is reliable. After review, the call from the field is overturned. There is no conclusive evidence that Neanderthals made art.
Why Does This Matter?
Artistic expression reflects a capacity for symbolism. And many people view symbolism as a quality unique to human beings that contributes to our advanced cognitive abilities and exemplifies our exceptional nature. In fact, as a Christian, I see symbolism as a manifestation of the image of God. If Neanderthals possessed symbolic capabilities, such a quality would undermine human exceptionalism (and with it the biblical view of human nature), rendering human beings nothing more than another hominin. At this juncture, every claim for Neanderthal symbolism has failed to withstand scientific scrutiny.
Now, it is time for me to go back to the game.
Who dey! Who dey! Who dey think gonna beat dem Bengals!