DNA ANALYSIS FROM CAVE PAINTINGS:

                

DNA from sediment reveals history of Denisova Cave. Image from phys.org.

For some time now it has been possible for scientists to extract DNA from the sediments in caves, including human and hominin DNA. This leads me to speculate that perhaps we may also be able to detect DNA from manually applied cave paintings such as positive handprints and get an analysis of the artists themselves. Considering that the human body sheds cells constantly it would seem logical that any paint on a cave wall that was applied by hand might contain detectable DNA in human skin cells shed during the application of that paint. And with the advances in DNA analysis this might be a way to personal data such as skin color, eye color, gender, and other data that would allow us to generate a detailed picture of the artist.

Denisova Cave sediment. Image from sci.news.

“Organisms are constantly shedding cells throughout their lives. Humans, for example, shed some half a billion skin cells every day. Much of this genetic material is quickly degraded, but some small fraction is safeguarded for millennia through sedimentary mineral-binding and is out there waiting for us to recover and study it. Now, we can conduct some remarkable research by recovering an immense diversity of environmental DNA from very small amounts of sediment, and in the total absence of any surviving biological tissues.” (Donovan 2020)

       

Negative handprint on cave wall. Online image, public domain.

For the negatively applied handprint, the kind where the hand is placed on the wall of the cave as a stencil and paint is blown around it to leave the image of the hand in outline, we usually assume that the paint was blown from the artist’ mouth. This paint sample should then have traces of human saliva as well as cells shed from the lining of the mouth that could be detected and analyzed.

Much like modern paints, ancient paints were combinations of pigments providing the color, binders hardening and preserving the paint, and the vehicle or liquid that carries the other ingredients for application. For ancient artists the pigments were invariably natural materials such as ochers, colored clays, charcoal, and less commonly plant dyes and materials. The binder could be natural fats, resins, plant saps, milk or eggs. Another possibility was urine used as a mordant (a chemical that fixes a dye or paint by combining with it to form an insoluble compound). In the case of milk used as a binder it also provides the vehicle (as would urine) but most commonly the vehicle would probably have been water (one benefit of mixing your paint with urine would have been that it would not have to have been carried separately, the artist would have a readily available supply).

“So how did the DNA get there? The researchers can’t say exactly, but it wouldn't be too difficult. Humans shed DNA constantly. Any traces of urine, feces, spit, sweat, blood or hair would all contain minute bits of DNA. These compounds actually bind with minerals in bone, and likely did the same with minerals in the soil, preserving it, reports Charles Q. Choi at LiveScience.” (Daley 2017) Once the science of DNA analysis was developed scientists used it to find what life forms had existed prehistorically in a place by testing undisturbed soil samples. The results were surprisingly rich turning up DNA from virtually every animal and insect that had passed that way, and stratigraphy allowed researchers to estimate timelines for those occupations.

“As Lizzie Wade at Science reports, when the team first sequenced the DNA from the sediments, they were overwhelmed. There are trillions of fragments of DNA in a teaspoon of dirt, mostly material from other mammals, including woolly mammoth, woolly rhinoceroses, cave bears and cave hyenas. To cut through the clutter and examine only hominid DNA, they created a molecular “hook” made from the mitochondrial DNA of modern humans. The hook was able to capture DNA fragments that most resembled itself, pulling out fragments from Neanderthals at four sites, including in sediment layers where bones or tools from the species were not present. They also found more DNA from Denisovans, an enigmatic human ancestor found only in single cave in Russia.” (Daley 2017) So, if DNA can be retrieved from cave soil there would seem to be no reason that it could not also be retrieved from paint. This, however, would depend on human contact with the paint.

Positive handprints. Image from Shutterstock.

In his 1993 paper on cave paint analysis Jean Clottes wrote “In the large cave of Niaux, direct observation and macrophotographs have shown that on the panels of signs dubbed ‘the signpost panels’, located were three passages branch off, the paint for some of the dots and red lines had been applied with fingers. On a few, even the fingerprints can be made out.” (Clottes 1993) So, we do have examples of manually applied paint and, since we know that human skin is constantly shedding cells from the outer surface we may be able to detect DNA in these examples. This would also apply to positive handprints where the paint was applied to the hand which was then pressed to the stone.

The other example I mentioned above is the negative handprint where the hand is placed on the wall of the cave as a stencil and paint is blown around it to leave the image of the hand in outline, we usually assume that the paint was blown from the artist’ mouth. This paint sample should then have traces of human saliva as well as cells shed from the lining of the mouth that could be detected and analyzed.

            

Positive and negative handprints, Cueva de los Manos,Argentina. Image from pinterest.

So, to what extent could we hope to use these techniques to learn about the artist’s genetics? “This ancient DNA appears to be relatively widespread. The scientists tested sediments from nine known archaeological sites in Belgium, Croatia, France, Russia and Spain. The sediments dated from between 14,000 and 550,000 years ago, with the oldest intact DNA found in sediments dating from 240,000 years ago.” (Henriques 2017) These examples cited do not distinguish between mitochondrial and nuclear DNA.

B. Vernot et al. (2021) have developed techniques to retrieve and analyze nuclear DNA to retrieve even more data. “Mitochondrial DNA has been retrieved from cave sediments, but provides limited value for studying population relationships. We therefore developed methods for the enrichment and analysis of nuclear DNA from sediments, and applied them to cave deposits in western Europe and southern Siberia dated to between approximately 200,000 and 50,000 years ago. We detect a population replacement in northern Spain approximately 100,000 years ago, accompanied by a turnover of mitochondrial DNA. We also identify to radiation events in Neanderthal history during the early part of the Late Pleistocene. Our work lays the ground for studying the population history of ancient hominins from trace amounts of nuclear DNA in sediments.” (Vernot et al. 2021)

Genetic analysis of DNA can provide a world of information about the person that the DNA came from. Such things as gender, hair, eye and skin color, and even susceptibility to some diseases could be determined. With DNA it would be possible to learn if a painter had contributed more than one image to a panel, or images in more than one location. It may also be possible to determine the group identity and population dynamics of the painters once a sufficient number of samples have been identified and analyzed. 

I am in no way a geneticist so I pass this suggestion to someone who is, perhaps a graduate student looking for a thesis project. Will it not be exciting to actually get to know a cave painter on an individual basis? I, for one, can hardly wait.

NOTE: Some images in this posting were retrieved from the internet with a search for public domain photographs. If any of these images are not intended to be public domain, I apologize, and will happily provide the picture credits if the owner will contact me with them. For further information on these reports you should read the original reports at the sites listed below.

REFERENCES:

Clottes, Jean, 1993, Paint Analyses from Several Magdalenian Caves in the Ariega Region of France, Journal of Archaeological Science, 1993, 20, pp. 223 - 235. Accessed online 4 August 2024.

Daley, Jason, 2017, Scientists Extract DNA From Ancient Humans Out of Cave Dirt, 28 April 2017, Smithsonian Magazine Online, https://www.smithsonianmag.com. Accessed online 6 August 2024.

Donovan, Michelle, 2020, Thousands of species recorded in a speck of soil, 10 September 2020, News release, McMaster University, Hamilton, Ontario, Canada.

Henriques, Martha, 2017, DNA from ancient humans discovered in 240,000-year-old soil, 27 April 2017, International Business Times, 4 August 2017. Accessed online 5 August 2024.

Vernot, B. et al., 2021, Unearthing Neanderthal population history using nuclear and mitochondrial DNA from cave sediments, Science, 15 April 2021, www.sciencemag.org. Accessed online 4 August 2024.