Saturday, January 14, 2017

PORTABLE PALEOLITHIC ART FROM PARPALLO CAVE, SPAIN - A REVIEW:


Engraved horse head,
 Parpallo cave-6, 
http://www.arte-coa.pt

"Parpalló cave is located in the Monduber Mountains, close to Gandia, in the province of Valencia, Spain. The cave was discovered by Vilanova y Piera in 1872.

The cave was excavated by L. Pericot between 1922 and 1931. The resulting stratigraphical record, which was recently revised, shows a timeline of occupation extending from the end of the Gravettian period, through the entire Solutrean period to the Mediterranean Upper Magdalenian, indicating a time interval approximately ranging from 28,000 years to 11,000 years before the present.
                       

Engraving,  Parpallo cave-6, 
http://www.arte-coa.pt

Besides the importance of the artefacts uncovered - stone tools and worked bone - the main reason for Parpalló cave’s position of prominence in the field of Palaeolithic art is due to the impressive collection of mobile art found in the cave. This mobile art includes more than 5,000 decorated limestone plates and blocks discovered during archaeological excavations." (http://www.arte-coa.pt/)


Parpallo cave-1, 
http://www.arte-coa.pt

"The mobile art of Parpalló is designed on bone (more than one hundred objects) and, predominantly, on the famous collection of thousands (5,034) of limestone plates and blocks as well as some pebbles. The designs are primarily of animals (mainly horses, goats, deer and bovines, as well as very rare carnivores and some birds) and abstract signs (consisting of complex linear shapes, such as waves, zigzags, dotted step shapes and swirl shapes, squares, etc.) and there is a single anthropomorphic design.



Parpallo cave-3, 
http://www.arte-coa.pt

This impressive set of artefacts was primarily produced using the technique of engraving. In some cases the figures were subsequently filled in by painting or by a combination of these two procedures (engraving and painting) within the initially defined space of the representations." (http://www.arte-coa.pt/)


The examples of portable art from Parpallo were created over a vast period of time indicating repeated occupations of the cave for the same length of time. Examples have been dated from 28,000 B.P. to 11,000 B.P., a record of at least 17,000 years in the one location illustrating evolving styles and influences. "Its relatively slow start, in terms of numbers, was during the Gravettian occupation (28,000 - 21,000 years before present). This stage encompasses only 7 plates, all with animal engravings and some with a painted interior".

"The next period, identified as the Solutrean (21,000 – 16,500 years before the present) includes the time said to be the peak of Parpalló mobile art. It is the phase when artistic expression and originality are at a maximum. This phenomenon, as it happens, can be generalised for all Palaeolithic art south of the River Ebro. No-one knows why this is so, but it could be due to the concentration of Palaeolithic communities in this area, which was likely an area of refuge from the worsening climate conditions that occurred at the height of the last ice age.

Accordingly, more than 150 plates have been dated to the Lower Solutrean (± 21,000 years before the present).


Parpallo cave-7, 
http://www.arte-coa.pt

More than 850 decorated pieces were attributed to the Middle Solutrean (± 20,000 – 19,000 years before the present), , - the development of some innovative aspects can be seen, such as the increased variety and complexity of geometric patterns and, above all, the significant increase in the size of the stones on which the engravings and painting are made. That increase in size, reaching half a metre in length in some cases, seems to want to convey the idea that the art of Parpalló wishes to leave its mark in stone.

The Evolved Solutrean (19,000 – 16,500 years before the present) comprises two distinct phases of development. The initial phase (Upper Solutrean), to which 915 pieces are attributed, encompasses a reduction to the size of the stone media, returning to their usual standard, as well as a sharp decrease in the use of the some pictorial elements, especially as regards animation and the representation of scenes. In the final phase of this period, known as the Solutrean-Gravettian, and represented by 558 objects.

The mobile art attributed to the Magdalenian period (16,500 – 11,000 years before the present) can also be divided into different phases, like the art of the previous period.

Hence, in the Lower Magdalenian (16,500 – 14,000 years before the present), the first phase of development (Ancient Magdalenian A) has links to some of the standards and norms of the preceding early Solutrean period i.e. a decrease in pictorial richness (less dynamics and detail, and even the evident regression of pictorial technique) and fewer pieces of art (323 plates). The standards and precepts are again reversed in the final phase of this period (Ancient Magdalenian B). This reversal comprises, in the first instance, an increase in the quantity of figures (671 pieces of art), as well as the establishment of the qualities that come to represent the essential characteristics of art of the late Pleistocene in Europe, i.e. the dominance of representations of animals, realism, respect for proportions and the attention to anatomical details. The Ancient Magdalenian B phase is also noted for the reappearance of geometrical patterns and their increased complexity and diversity.

Finally, the Upper Magdalenian (14,000 – 11,000 years before the present) is represented through 440 objects (including stone plates and engraved bone tools). The trend for naturalist representations in this period entails continuity of the processes initiated in the previous stage."
(http://www.arte-coa.pt/)


Parpallo cave, 
http://www.arte-coa.pt

A recent study published in the online journal PLOS studied the pigments used to paint the Parpallo Cave plaquettes by energy dispersive X-ray fluroescence spectometry (EDXRF), for 73 sides with red paint from 67 plaquettes, and 15 sides with yellow images from 14 plaquettes. Samples were also studied under Fourier Transform Infrared spectroscopy (FT-IR) to confirm the EDXRF findings. These confirmed that all red and yellow pigments used at Parpallo were iron based (oxides and/or hydroxides) with the addition of a large number of elements in smaller amounts such as arsenic, manganese, and lead (Garcia et. al. 2016). We are rushing into an era where the study of rock art can be viewed in many aspects as a hard science. For full details of this interesting study I will direct you to the original paper listed below.

NOTE: The images used to illustrate this review were retrieved from the Internet with a search for Parpallo Cave Art Public Domain. If any of these images were not public domain I apologize to the owners of the rights to the image.

REFERENCES:
http://www.arte-coa.pt/index.php?Language=en&Page=Saberes&SubPage=ArteAlemCoa&Menu2=Parpallo

Garcia, Clodoaldo Roldan; Bonilla,Valentin Villaverde; Marin, Isabel Rodenas, and Mascaros, Sonia Murcia,
2016   A Unique Collection of Palaeolithic Painted Portable Art: Characterization of Red and Yellow Pigments from the Parpalló Cave (Spain), PLOS, http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0163565

Saturday, January 7, 2017

CAVE ART PROVIDES A CONFIRMATION OF A HYBRID BISON SPECIES IN PALEOLITHIC EUROPE:


Male European bison, Poland.
Rafal Kowalczyk.


European bison, Poland.
Rafal Kowalczyk.

From time to time we hear discussion of the possibility of using cave paintings and other rock art to add to scientific knowledge by identifying animals by species for a given time period and/or location. We now may have an example of just that. Writing in Smithsonian.com of October 19, 2016, Jason Daley reported on a paper from Science by Jessica Boddy that announces that genetic testing, confirmed by cave art, has discovered an unknown species of European bison. Named the "Higgs Bison", a tongue-in-cheek reference to the Higgs Boson particle only recently detected by physicists after a 50-year search.

First detected when a team at the Australian Centre for Ancient DNA at the University of Adelaide, led by Alan Cooper, began sequencing DNA from ancient European bison looking for past impacts of climate change. The DNA from many of the bones had a different genetic makeup to anything they had previously known, which looked to them like a new species.


Aurochs, Lascaux Cave, France.
Photograph public domain.

"The researchers dubbed the creature Bison-X and Higgs Bison. Furtheer examination of the DNA showed that this new animal was actually a hybrid between the steppe bison and the aurochs, a species of wild cattle believed to be the ancestor of modern cows Beyond that the researchers knew very little about the animal including what it looked like." (Daley 2016)


Aurochs, Lascaux Cave, France.
Photograph public domain.

"Cooper contacted French cave researchers to see if the animal might have been captured by the hunters who decorated the caves of Lascaux and Pergouset. And indeed there was a record of this creature." (Daley 2016)


Steppe bison, Chauvet cave, France.
httpwww.zmescience.com - public domain.


Steppe bison, Chauvet cave, France.
httpwww.zmescience.com - public domain.

They found that images of cave bison which could be dated to between 18,000 to 22,000 years ago clearly depict the steppe bison with its long horns and stout forequarters. However images from 5,000 years later show a creature without such a barrel chest and thinner horns. Researchers of cave art had previously assumed that the differences were ones of style and regional variation in portrayals.

Researchers believe that the shift in dominant types was likely due to the periodic changing climates in the Paleolithic period. "Cooper and his colleagues traced the Higgs Bison back over 120,000 years using DNA from fossil bones from Europe, the Urals and  the Caucusus Mountains, according to a press release. During warm spells, the steppe bison was the dominant bovine in western Eurasia. During cold spells, the fossil record suggests that the hybrid animals did better. While the steppe bison eventually went extinct, Higgs Bison survived and is the ancient ancestor of modern European bison." (Daley 2016)

"'Once formed, the new hybrid species seems to have successfully carved out a niche on the landscape, and kept to itself genetically,' Cooper says in the press release. 'It dominated during colder tundra-like periods, without the warm summers, and was the largest European species to survive the megafaunal extinctions.'" (Daley 2016)

Wisent, Higgs bison, Lorblanchet cave,
 France. www.zmescience.com. 
Public domain.


Wisent, Higgs bison
Public domain.

One contributing factor in the large difference observed in the genome of the Higgs Bison compared to the European Bison is that the modern European Bison went through a genetic bottleneck. During the 1920s the population declined to only 12 animals so the genome looks quite different from its ancient ancestors. (Daley 2016)

With the origin of the hybrid bison traced back to approximately 120,000 years we now have to wonder if the North American bison also carries the genetic markers of the hybrid species. There would have been plenty of opportunity for them to enter North America across Beringia. Careful analysis of North American rock art and genetic testing of Bison bison DNA could reveal new information as well.

(Read the whole story at: http://www.smithsonianmag./smart-news/how-cave-art-helped-dig-new-animal-species-180960833/#lcLx3TozUKrd8Hah.99)

REFERENCE:

Daley, Jason
2016       Cave Paintings Help Unravel the Mystery of the 'Higgs Bison', http://www.smithsonianmag.com, October 19, 2016

Saturday, December 31, 2016

2016 C.R.A.P. AWARD GOES TO UTAH SENATORS ORRIN HATCH AND MIKE LEE, AND CONGRESSMAN JASON CHAFFETZ:

It is once again time for RockArtBlog to award the coveted annual C.R.A.P. (Certifiable Rock Art Prevarication) award for what is one of the year's biggest rock art related prevarications. This year's 2016 award goes to Utah senators Orrin Hatch and Mike Lee for their legislative attempt to block the creation of Bear's Ears National Monument in southeastern Utah, to protect uniquely beautiful lands as well as amazing cultural resources including a large quantity of rock art. A late addition to this prestigious pool is Utah congressman Jason Chaffitz. 


Rock art in proposed Bear's
Ears National Monument.
http://img.deseretnews.com

According to Thomas Burr of the Salt Lake Tribune (published on September 15, 2016) "Utah Sens. Orrin Hatch and Mike Lee introduced the legislation Thursday to exempt the state from a law allowing the president to designate new national monuments, but critics dismissed the move as a desperate 'Hail Mary' in trying to halt protection of the Bear's Ears region in southeastern Utah."

"The measure would prohibit the president's use of the 1906 Antiquities Act within Utah, extending a loophole that now covers Wyoming, as part of an effort to keep President Barack Obama or his successors from using the unilateral power to create national monuments."
Rock art in proposed Bear's
Ears National Monument.
Photo: Shanna Lewis, httpwww.cpr.org

Senator Lee stated "New Yorkers would not appreciate it if Utahns came in and told them what they could and couldn't build in Manhattan, and Utahns don't like it when out-of-state special-interest groups tell us how to use our land either. Over 50 years ago, the state of Wyoming was granted protections from Antiquities Act abuse in their state, and all Utahns are asking is for that same protection to be extended to their state. (The 1950s legislation creating an expanded Grand Teton National Park was passed with the significant concession to opponents that the Antiquities Act would not again be used in Wyoming without the consent of Congress.)" (Burr 2016)

Rock art in proposed Bear's
Ears National Monument.
Photo: Tim Peterson, http://d1jrw5jterzxwu.cloudfront.net

Hatch explained his opposition to the monument with the statement "today, we are again faced with the threat of a unilateral designation of another 1.8 million-acre monument in southeast Utah," Hatch said. "Such a designation would far exceed the purpose of the Antiquities Act, which was written specifically to protect special cultural sites and objects limited to the smallest compatible area necessary." (Burr 2016)


Rock art in proposed Bear's
Ears National Monument.
natgeocreative.com, Public Domain

A representative for the pro-designation effort explained that "Senator Lee confuses private land in New York for the public lands in Utah that belong to all Americans," said Jen Ujifusa, legislative director of the Southern Utah Wilderness Alliance. "The Utah delegation had three years to develop a meaningful and reasonable conservation solution with the Public Lands Initiative, but squandered that opportunity by listening only to industry and parochial interests. This last-ditch Hail Mary shows they know the PLI has failed." (Burr 2016)

In a related internet report on Newsmax.com, on December 29, 2016, Karl Nelson, quoted Utah congressman Jason Chaffetz "The midnight move is a slap in the face to the people of Utah." (Nelson 2016)

"Obama said in a statement that the monument will 'protect some of our country's most important cultural treasures, including abundant rock art, archaeological sites, and lands considered sacred by Native American tribes.'" (Nelson 2016) Please note the wording in President Obama's statement above. This might be the first time that the President of the United States has said the words "rock art" in a press conference, a historic occasion!

It seems to me that this opposition is somehow missing the point. The National Monument designation is intended to protect this wonderful place from mining and petroleum production, uncontrolled four-wheel driving and dirt-biking, and pot-hunting and vandalism of cultural remains and rock art. How is protection a bad thing? Hatch, Lee, and Chaffitz, for their support and advocacy of vandalism and destruction, in this case, are awarded the RockArtBlog 2016 C.R.A.P. award. Congratulations gentlemen.

NOTE: The photographs illustrating this story were retrieved from the internet through a search for "Bear's Ears rock art public domain". If any of them were used mistakenly without permission I apologize.

PS: As of December 29, 2017, President Obama has signed the order to make Bear's Ears a National Monument. President-elect Trump and the Republicans in congress are vowing to overturn it after the change of office in January. I may have to enlarge the recipient pool of the C.R.A.P. award to include the whole Republican party.


REFERENCES:

Burr, Thomas,
2016     Hatch,Lee seeking Utah exemption from monument-creating Antiquities Act, WWW.SLTRIB.COM, Sept. 16, 2016.

Nelson, Karl
2016     Chaffetz Slams Obama 'Midnight Land Grab', Newsmax.com.

Friday, December 23, 2016

MERRY

 CHRISTMAS

2016

From
RockArtBlog


     Santa  Dasher   Dancer   Prancer  Vixen   Comet   Cupid   Donner   Blitzen   Rudolph

Who forgot the

sleigh?

Photograph courtesy of Robert Dundas


Saturday, December 17, 2016

NEW ROCK ART DISCOVERIES IN JORDAN:




Petroglyphs found in the
Black Desert of Jordan.
Photo: Peter Akkermans.

A November 21, 2016, article on LiveScience, written by Owen Jarus, covers the recording of "thousands of inscriptions and petroglyphs dating back around 2,000 years - in the Jebel Qurma region of Jordan's Black Desert." (Jarus 2016) The article details discoveries by a team led by Peter Akkermans, of  The Netherlands Leiden University, who leads a study project at Jebel Qurma. "Nowadays, the Jebel Qurma area, and the Black Desert in general, is a highly inhospitable area, very arid and difficult to cross," said Akkermans.


Petroglyphs found in the
Black Desert of Jordan.
Photo: Peter Akkermans


Petroglyphs found in the
Black Desert of Jordan.
Photo: Peter Akkermans

"The inscriptions are written in Safaitic, and alphabetic script used by people who lived in parts of Syria, Jordan, and Arabia in ancient times." (Jaris 2016) The team's discoveries show that the Jebel Qurma area had trees, wildlife, and a large human population around 2,000 years ago.


Petroglyphs found in the
Black Desert of Jordan.
Photo: Peter Akkermans


Petroglyphs found in the
Black Desert of Jordan.
Photo: Peter Akkermans

"The petroglyphs, or rock art, show images of lions, gazelles, horses, and large birds that may be ostriches. The inscriptions found near these petroglyphs tend to be very short. "Most of the texts are simply names, like so-and-so, the son of so-and-so," Akkermans said.  A few inscriptions suggest that the population of Jebel Qurma had conflicts with the people of the ancient city of Petra, the Nabataeans. (Jarus 2016)


Petroglyphs found in the
Black Desert of Jordan.
Photo: Peter Akkermans

"Other inscriptions tell of  the challenges and setbacks encountered by the people who lived at Jebel Qurma. "May there be strength against hunger," one inscription reads, while another was written by a man who said he was 'distraught over his beloved.'" (Jarus 2016)

The changes in habitability indicated by the petroglyphs and inscriptions should be seen in light of our present challenges caused by climate change. If such major environmental changes can happen under natural conditions in a relatively short time, under essentially natural conditions, what kinds of changes can we expect in the relatively near future under conditions of increasing global warming caused by human activities? Perhaps we should take this as a serious warning.

Note: to see the full article visit LiveScience at http://wwwllivescience.com/56944-ancient-inscriptions-found-in-black-desert.html.

REFERENCE:

Jarus, Owen,
2016    Ancient Inscriptions Show Life Once Flourished in Jordan's 'Black Desert', LiveScience, November 21, 2016, http://wwwllivescience.com/56944-ancient-inscriptions-found-in-black-desert.html.

Saturday, December 10, 2016

METEOROLOGICAL RECORDS IN ROCK ART - CHINESE CAVE INSCRIPTIONS:



Chinese drought inscription,
Davu Cave, Qinling mountains,
China. From Ghose, LiveScience,
August 20, 2015.

A subject in rock art that has long fascinated me is evidence of verifiable events recorded on the rocks. As everyone's daily life is directly impacted by meteorology, that is one area that we should expect to find evidence of in rock inscriptions or pictures. An example of this can be found in inscriptions in Davu Cave, in southeastern China. Located in the Qinling Mountains, this cave contains written inscriptions of droughts occurring in the region and their impact upon the population.

Writing for LiveScience on August 20, 2015, Tia Ghose cited an August 13 article from the journal Scientific Reports that outlined a series of droughts in that area and the inscriptions that record them. The droughts were confirmed by analysis of chemical elements in stalagmites from the cave. Study co-author Sebastian Breitenbach, a paleoclimatologist at the University of Cambridge, England explained that the team analyzed the proportions of carbon, uranium, oxygen, and other isotopes, in stalagmites  to detect climate changes over time that signaled droughts." The amounts of radioactive uranium and carbon, which decay at a known rate, tied specific parts of the stalagmite to particular historic times." (Ghose 2015)  And, "because the water seeping into the cave was likely groundwater, the levels of oxygen and carbon isotopes could provide information about surface conditions outside the cave. The team found that oxygen and carbon levels rose when rainfall was low, suggesting that those markers could reliably reveal when drought conditions occurred." (Ghose 2015)

Comparing this scientific record then with cave inscriptions revealed a very accurate correlation.

"One inscription, which is dated to July 27, 1596, says directly that there is a big drought, and that the writers had come to the cave to get water and pray for rain. Another, dating to 1891m reads: 'On May 24th, 17th year of the Emperor Guangxu period, Qing Dynasty, the local mayor, Huaizong Shu, led more than 200 people into the cave to get water. A fortune-teller named Zhenrong Ran prayed for rain during the ceremony.'" (Ghose 2015)

"Another inscription mentions a Dragon Lake that may have been in the cave." (Ghose 2015)

All in all, records of seven droughts over the past 500 years corresponded quite well with the recorded droughts in the cave formations. The team even used their data from the chemical record and the inscriptions to construct a model to predict future periods of drought in that region. That model predicts that "in the next decade, China is in for more severe and more frequent droughts, though the model can't predict exactly where or when the droughts will occur." (Ghose 2015)

Rock art, not only as a record of the past, but as a predictor of the future. How about that?

REFERENCES:

http://www.livescience.com/51929-cave-graffiti-reveals-drought.html

Saturday, December 3, 2016

MYTHOLOGY IN ROCK ART:

We have long been convinced that mythology could offer insights into the meaning of rock art. I am sure that we all know of examples where we are convinced that this works, that the meaning of a rock art panel can be inferred by knowledge of the mythology of the people who created it. Now an article in the December 2016 issue of Scientific American makes the fascinating claim that mythology can be used to decipher meaning in cave art produced during the Paleolithic period.



Drawing of the Polyphemus
myth panel in Les Trois-Freres. 
Public domain.

Julien d'Huy, in The Evolution of Myths, explains his process of phylogenetic analysis using statistics to generate "phylogenetic trees (that) reveal that species of myths evolve slowly and parallel patterns of mass human migration out of Africa and around the globe." (d'Huy 2016:64)

D'Huy explained that "my phylogenetic studies make use of the extra rigor of statistical and computer modeling techniques from biology to elucidate how and why myths and folktales evolve." (d'Huy 2016:64)

One of the myth families that he has applied this technique to is the "Cosmic Hunt", where "a man or an animal pursues or kills one or more animals and the creatures are changed into constellations." (d'Huy 2016:64) This story, in a number of variations, was common to the ancient Greeks in the story of Callisto who becomes the constellation Ursa Major, the great bear, and to the Iroquois, Chukchi, and Finno-Ugric tribes of Siberia. According to d'Huy "although the animals and the constellations may differ, the basic structure of the story does not." (d'Huy 2016:64)

D'Huy has traced the Cosmic Hunt myth back through history and around the world. He found it to be "nearly absent in Indonesia and New Guinea an very rare in Australia, but present on both sides of the Bering Strait, which geologic and archaeological evidence indicates was above water between 28,000 and 13,000 B.C. The most credible working hypothesis is that Eurasian ancestors of the first Americans brought the family of myths with them." (d'Huy 2016:65)

Another myth family that d'Huy has traced back to early origins is known as the Polyphemus myth after the one-eyed giant in the Odyssey who trapped Ulysses' crew in a cave and devoured some of them. In the same way as Polyphemus kept his herd of sheep in a cave, in variations of this myth animals are kept concealed by a trickster or other being, and a hero bring them to the surface of earth to sustain the people. The Algonquin Blackfoot people acquired buffalo in this way. "A composite phylogenetic tree of Polyphemus myths indicates that the stories followed two major migratory patterns: The first, in Paleolithic times spread the myth in Europe and North America. The second, in Neolithic times, paralleled the proliferation of livestock farming." (d'Huy 2016:68)


Drawing of the hero in the
Polyphemus myth panel in
Les Trois-Freres. Public domain.

"Phylogenetic reconstructions of both the Polyphemus and Cosmic Hunt stories build on decades of research by scholars who based their work primarily on oral and written versions of folktales and legends. The current models also incorporate empirical observations of mythological motifs in prehistoric rock art. Similarities in certain rock art motifs and the reconstructed stories open a new window on the mental universe of the first humans who migrated across the Bering Strait to the New World between 30,000 and 15,000 years ago. 
In the myth of Polyphemus, as its original public most likely heard it, a hunter faces one or many monsters that possess a herd of wild animals. He enters the place where the monster keeps the animals and finds his way out blocked by a large obstacle. The monster tries to kill him. The hero manages to escape by clinging to the underbelly of one of the animals.
This protomyth - revealed by three separate phylogenetic databases, many statistical methods and independent ethnological data - reflects the belief, widely held by ancient cultures, in the existence of a master of animals who keeps them in a cave and the need for an intermediary to free them." (d'Huy 2016:69)


Drawing of the hero of the
Polyphemus myth panel in
Les Trois-Freres. Public domain.

D'Huy believes that this theme to can be applied to the Paleolithic world view on the origin of game. "At the Cave of the Trois-Freres (or "three brothers")
in the French Pyrenees, frequented during the upper Paleolithic, a panel shows a small creature with the head of a bison and the body of a human, which seems to be holding a short bow. Lost in the middle of a herd of bison, another animal, similar to a bison, turns its head toward the human hybrid, and the two exchange gazes." (d'Huy 2016:69)

This, he sees as an illustration of the herd of game animals being brought out of concealment (hidden in the cave perhaps) by a hero, to the people.
Now I have been relatively critical of statistical analysis in the past, especially when applied to rock art, but even without relying on statistics this explanation makes a great deal of sense, and when combined with the phylogenetic analysis of the mythology, I have to concede that I believe there is something here that is possibly of great importance to rock art studies. I look forward in the future to more contributions by Julien d'Huy. 

NOTE: Read the whole article in the December 2016 Scientific American magazine.

REFERENCE: 

Julien d'Huy,
2016  The Evolution of Myths, Scientific American, December 2016, Volume 315, Number 6, pages 62 - 69.