Tuesday, June 10, 2014

Knives, Forks, Overbites, Brains, and Neanderthals: Anthropology Reveals Its Secrets

In 2011, Kathleen McAuliffe published a fascinating article in Discover magazine: If Modern Humans Are So Smart, Why Are Our Brains Shrinking? Her article and its implications are discussed here.

McAuliffe was startled to learn that anthropologists (paleoanthropologists) had discovered the human brain had been shrinking in size over the last 20,000 years but neglected to tell anyone about it.

"As I soon discover, only a tight-knit circle of paleontologists seem to be in on the secret, and even they seem a bit muddled about the matter. Their theories as to why the human brain is shrinking are all over the map."

There was quite a bit of interest in this finding. In an era when many researchers seem intent on having their conclusions and hypothesis published simultaneously in scholarly journals and in the New York Times, this seeming lack of interest in publicity is surprising.

In 2012, Bee Wilson published her book Consider the Fork: A History of How We Cook and Eat in which she revealed another anthropologic secret of great interest. She revealed that the manner in which our top incisors overlap and close over our lower teeth "like a lid on a box" to produce an overbite has only recently occurred in our society.

"….the overbite is a very recent aspect of human anatomy and probably results from the way we use our table knives. Based on surviving skeletons, this has only been the ‘normal’ alignment of the human jaw for 200 to 250 years in the Western world. Before that, most human beings had an edge-to-edge bite, comparable to apes. The overbite is not a product of evolution—the time frame is far too short. Rather, it seems likely to be a response to the way we cut our food during our formative years."

Wilson points out that the timing of this transition to an overbite is consistent with a change in table manners, not a change in diet.

"What changed substantially by the late eighteenth century was not what was eaten but how it was eaten. This marked the time when it became normal in upper- and middle-class circles to eat with a table knife and fork, cutting food into little pieces before it was eaten."

Eventually, this dining habit trickled out to the rest of society and became the norm. It would only take a generation for this change in habit to initiate the change in the structure of our teeth. For this to have been observed suggests that the growth of our upper front teeth must have been inhibited by constant pressure from the food ingested. Presumably, people were biting and/or tearing food with their front teeth with sufficient force to change the position and extent of the teeth.

Wilson attributes the evidence and explanation of this transition to Charles Loring Brace, an anthropologist at the University of Michigan. Brace provided the most compelling data to support this hypothesis in China. The Chinese had long ago developed the habit of cutting their food into small pieces before cooking and eating it. Brace was able to observe the "pickled" remains of a young man that dated back to the era when the use of chopsticks in eating became common. He was thrilled to discover the young man had a generous overbite.

"Over subsequent years, Brace has analyzed many Chinese teeth and found that—with the exception of peasants, who often retain an edge-to-edge bite well into the twentieth century—the overbite does indeed emerge 800-1,000 years sooner in China than in Europe."

Brace, who seemed to prefer the appellation C. Loring Brace, is an interesting person. The University of Michigan produced a long summary of his work. The word "overbite" appears only once, and that is in the title of a thesis produced by one of his students. The most concise summary of his conclusions on the origin of the overbite is probably a short three-page note submitted as a "Commentary" in American Anthropologist. He provides this background:

"My interest in the form of the bite was originally stimulated….by Coon’s observations-in my case by reading his account of the relation between age and occlusal form in the mountains of northern Albania in1930 (Coon 1950….). Coon raised questions concerning the possible role played by changes in foodstuffs and eating habits, but he wisely avoided any summary judgment other than noting that the difference between an edge-to-edge bite and an overbite was not genetically determined."

Similar observations were made as far back as the 1930s.

"Others also have noted that, in such diverse examples as Australian Aborigines (Price 1938, 1939; Brace 1980) and Eskimos (Price 1936, 1939; Waugh 1937), the change from an edge-to-edge to an overbite took place in the space of a single generation. The association between this change and the adoption of the diet of Western "civilization" has been duly observed."

He attributes the dental transition not to changes in diet but to changes in the way food was eaten.

"Prior to that point, the accepted method of reducing ingested food to bite-sized proportions was to grasp it with the fingers of the left hand and thrust a portion into the mouth to be gripped by the front teeth and sliced off at lip level with the knife held in the right hand —what I have referred to as the "stuff and cut" school of etiquette (Brace 1977….). Practiced since childhood, it would be this that prevents the continuing eruption of the incisors which is the source of the overbite."

With the modern use of knife and fork:

"The role of the incisors as clamps ceases at that moment, overeruption is no longer opposed, and the result is the deep modern overbite that is now thought of as being ‘normal’."

The "creation" of the overbite, coupled with the "stuff and cut school of etiquette" would be the makings of a book by an enterprising contemporary scientist. One might envisage talk show appearances and, perhaps, tales of self mutilation as amateurs tried to reproduce the eating technique. However, Brace’s passion was focused elsewhere.

His main interest was in Neanderthals and their relationship with the species generously referred to as Homo sapiens. He believed that the fossil evidence was consistent with the notion that modern humans were descendents of the Neanderthals. From Wikipedia:

"Brace argued that cultural factors, especially the increased use of tools by Neanderthals, produced morphological changes that led the classic Neanderthals to evolve into modern humans."

Brace’s view was controversial. Others took an almost exactly opposite view that Neanderthals were rendered extinct, one way or another, after interacting with modern man and had little effect on the evolution of today’s humans. Recent evidence from the sequencing of the Neanderthal genome resolves that controversy, or, at least, it moves it to a different plane.

Steven Mithen provided an article for The New York Review of Books: Most of Us Are Part Neanderthal. He discusses the work of Svante Pääbo and his collaborators in acquiring and mapping the Neanderthal genome as presented in Pääbo’s book Neanderthal Man: In Search of Lost Genomes.

What has this research concluded?

"Pääbo and his team were able to determine that the modern human and Neanderthal lineages had split between 270,000 and 440,000 years ago, a conclusion that confirmed existing views. Far more surprisingly, however, they concluded that people outside of Africa, whether Europeans or Asians, have up to 5 percent of their DNA derived from Neanderthals. The most likely scenario is that a group of modern humans left Africa sometime around 50,000 years ago, interbred with Neanderthals in the Middle East, and then went on to populate the world, taking the Neanderthal DNA with them. That DNA would have been diluted with every generation of humans but its persistence into the present day suggests that some of the Neanderthal gene variants have provided modern humans in Europe and Asia with enhanced adaptive capabilities over their African Homo sapiens forebears."

And then there is this note on how little separates us from the other species of apes.

"The nature and extent of the differences between Neanderthals and Homo sapiens—the gap—remain as vigorously debated as ever. Pääbo and his team identified the molecular gap between them. There are seventy-eight amino-acid-altering nucleotide positions—"meaningful mutations"—in which all humans today are similar to one another and different from Neanderthals and the apes. Pääbo suspects that this number will reach two hundred as the sets of data are refined but even that will be only a tiny proportion of the complete human genome."

"These amino acid differences arose from mutations after the lineage divide that led to the emergence of both Neanderthals and Homo sapiens from a common ancestor. They influence the proteins that build tissues and the mind. Considering that there are more than 20,000 proteins encoded by the genome, a mere seventy-eight (or even two hundred) mutations seem a tiny genetic gap—but the behavioral consequences might be vast. Regrettably, we have little idea of any such consequences. Pääbo confesses all: ‘The dirty little secret of genomics is that we know next to nothing about how a genome translates into the particularities of a living and breathing individual.’ As such, despite all we know about ancient DNA, arguments about the relative cognitive capabilities of modern humans and Neanderthals remain reliant on interpretations of the archaeological data."

The fate of the Neanderthals is unknown, but this data demonstrates that the two species interacted in such a way as to allow mating. So, in a sense, Brace was correct. Most of us are descendents of Neanderthals. One suggested explanation for their disappearance is that they were assimilated into Homo sapiens and disappeared as a separate entity. That would make him a bit more correct.

One wonders what Brace thinks of all this.

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