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Teeth, Dirty and Otherwise
Recently I received a card from my dentist’s office advising that I’m due for my 6-month cleaning and checkup. I’m fortunate in that, except for four wisdom teeth pulled over 50 years ago, I have my original teeth, albeit three are crowned. Over the years, various dentists and dental hygienists have complimented me on the cleanliness of my mouth. I’ve often wondered just how "dirty" some mouths are and whether I am actually brushing and flossing too diligently. In contrast, Tuesday’s December 2 Star-Ledger contained an Associated Press item headlined "Secrets of the ages revealed in dirty teeth".
Clearly, the 6 to 8 individuals whose teeth were the subject of the article could have used some modern day tooth cleansing products. The article dealt with the work of Dolores Piperno at the Smithsonian Tropical Research Institute and archeology professor Tom Dillehay at Vanderbilt University. These two researchers looked at dental plaque scraped from the teeth of inhabitants of an ancient village in Peru dating back from 5,500 to 9,200 years ago.
Even after all these millennia, the scientists were able to identify traces of the food eaten by those ancient people. The plaque contained bits of cultivated crops such as beans, squash and peanuts and grains. Starch grains were found on most of the 39 teeth examined in the study, published on the December 1 online edition of the Proceedings of the National Academy of Sciences. Some of the grains had been cooked. The stable diet over thousands of years reveals much about the staple nature of the society back in those days. The researchers hope that similar studies on the teeth of Neandertals and early modern humans will reveal any differences in diet between us and our early cousins.
So far, we’ve talked about stuff found on teeth. In the past, we’ve discussed studies of the composition and structures of teeth themselves. For example, in my column of 11/13/2003, we discussed studies on the composition of Oetzi, the Iceman’s teeth that yielded information on his travels prior to his demise. Akin to trees forming rings as they grow, as teeth grow microscopic lines are laid down on the surface of teeth. According to an article " The Birth of Childhood" by Ann Gibbons in the November 14 issue of Science, lines are laid down on a weekly basis. (I must check whether this "weekly" thing is really a precise description or a qualitative approximation.)
Concerning childhood, the question is when did our relatively long human childhood came into play. Let’s compare ourselves with our chimpanzee cousins and with our hominin relatives such as the famed Lucy, an Australopithecus afarensis, or our more closely related ancestor Homo erectus. One thing that stands out is the length of our childhood when compared to the childhoods of those other distant relatives. The bottom line is that we modern (Homo sapiens) humans live a slower life, taking longer to reach various stages of childhood and adulthood than our primate cousins. We also live longer. (I saw Willard Scott celebrate a gal who, as I recall, was either 109 or 112 on the Today show last week.)
Teeth can be used as markers for certain milestones in childhood. For example, eruption of the first molar roughly corresponds to the age when a child can more or less survive on its own. In a chimpanzee, the first molar erupts at about 3.5 to 4 years and it’s at that age that a chimp can, with help from other chimps in the way of sharing food, survive after losing its mother. The Science article begins with the case of Mel, a chimp whose mom died when Mel was only 3.5 years old. Mel was in trouble but managed to survive by begging for food and "persuading" two adult chimps to share food with him. They also provided protection and a place to sleep by their sides. Mel lived until he was ten.
A modern human child generally has its first molar appear at around 6 years of age. Up until that age, children rely on their parents to feed them. At about six, there’s some degree of independence as witness the fact that, according to Gibbons, street children around the world have to be at least 6 or 7 years old to have a chance of surviving without parental care. Mel the chimp appears to have had the smarts to survive in his society at only three and a half years old. Scientists wonder at what point in time did human childhood become or start to become significantly longer than the childhoods of our primate cousins, the chimps.
Fossils of ancient hominin children are rare and back in 1925 one Raymond Dart announced the finding of the skull of a child, an australopithecine, that Dart called the Taung baby. Based on the nature of the skull and the fact the first molar had erupted, Dart estimated the child was 6 years old when it died some 2 million years earlier. Since then, teeth of other australopithecine children were found and in 1984 Christopher Dean and Timothy Bromage at University College London decided to count the lines in the teeth of these children. Their results shocked the workers in the field. The children weren’t 6 years old but were only about 3.5 years old. Their childhood, as marked by the eruption of the first molar at least, was more like the current chimpanzees than today’s modern humans.
Attention then turned to Homo erectus, which had a bigger brain and other features more akin to those of us modern humans than did the australopithecines. One of the very few remains found of a Homo erectus youth was a 1.6 million-year-old skeleton of a boy who died near Lake Turkana in Kenya. The skeletal features and the brain size suggested that the boy was 13 years old when he died. He was tall, 5 feet 4 inches, and weighed about 110 pounds. Australopithecines were smaller in stature. Gibbons cites work in press by Dean and Tanya Smith and by others on the Turkana boy that conclude from tooth studies and skeletal structure that he was actually only 8 to 10, most likely 8 years old when he died. It seems that Homo erectus lived a faster life than we do.
Another marker in the childhood picture is the eruption of the third molar, which also corresponds roughly with the age of first breeding in the female. I presume that this should correspond to the end of childhood, although some of the well publicized behaviors of various celebrities might contradict this assumption. At any rate, the eruptions of the third molar occur at about 11.5 years in both chimps and australopithecines, compared to an estimated 14.5 years for Homo erectus. As for us modern humans, the third molar eruption for Homo sapiens is 19.3 years. Obviously, the correlation of third molar eruption with age of first breeding is a statistical one with many females breeding much younger and others much older in this age of raging hormones and on the other extreme efficient birth control.
Well, I’m not going to come to any conclusion about when childhood began to lengthen appreciably for the human species. Other studies have been made on Homo sapiens children’s teeth. One such study was on the tooth lines in a child that lived in Morocco 160 thousand years ago. The conclusion was that this 8-year-old child had grown as slowly as a child of today. This would indicate that our prolonged childhood has been around only in our Homo sapiens species, which evolved some 200 thousand years ago. However, let’s not rule out those pesky Neandertals, who haven’t been fully evaluated yet. In recent years we’ve been reading of studies showing that they weren’t the doltish brutes that they were formerly thought to be.
Speaking of childhood, perhaps another marker of childhood for those children who celebrate Christmas is changing views on Santa Claus. I suspect that the first molar eruption at around 6 years of age correlates roughly with the time at which serious doubts about Santa emerge or even solidify. If the third molar eruption does indeed correspond very approximately with the time of first breeding, the Santa concept reappears and gifts are given to the young offspring. The cycle repeats with grandchildren but, by the time those molars have departed or are capped with gold, Santa has disappeared and gifts have been replaced by cash. At least that’s the case for the 80-year-olds I have surveyed.
Allen F. Bortrum