ABSTRACT
A major determinant of tooth architecture is the arrangement of lines in dentin and in the enamel following the contour of the surface. Since the original description of these lines in the 19th century, they have been attributed to recurring events during tooth development. They have also attracted the attention of dental scientists and anthropologists; however, to date, studies of these structures have been largely theoretical and microscopic. We show here that the statistical properties of the spacing between the lines are similar in teeth from both ancient and modern humans and from extinct archosaurs, reptiles that lived tens or hundreds of millions of years ago-they also resemble heart rate variability of living humans. We propose that the deposition of these recurring structures is controlled by the autonomic nervous system. This control accounts for their regularity and recurrent nature and implies that the lines are an expression of a biologic rhythm which has been conserved throughout evolution. Details of the rhythms give clues to life styles in ancient civilizations and to the physiology of extinct archosaurs.
Subject(s)
Autonomic Nervous System/physiology , Models, Biological , Odontogenesis/physiology , Tooth/growth & development , Animals , Heart Rate/physiology , History, Ancient , Humans , Paleodontology/methods , Reptiles , Statistics, NonparametricSubject(s)
Dental Plaque/prevention & control , Toothbrushing/methods , Female , Humans , Male , Time FactorsABSTRACT
"This article addresses the impact age and presence/number of children have on the remarriage probabilities of divorced women [in the United States]. Following Koo and Suchindran..., an interaction between these two factors is posited, with children having an effect on the remarriage chances only of younger and older women. In addition, a third factor, dissolution measurement, is considered because remarriage intervals measured from separation and from divorce can be quite different." The data are from the 1973 National Survey of Family Growth. "Analyses conducted separately by race indicate that (1) dissolution measurement can make a difference in the estimated effect of both age and presence/number of children on remarriage probabilities for both blacks and whites, (2) net of numerous controls, older women and women with more children of both races tend to remarry at the slowest pace, and (3) age and presence/number of children interact for whites but not for blacks."
