Abstract
The life history pattern of recent humans is uniquely derived in many of its aspects including an extended post-reproductive lifespan combined with short interbirth intervals. A number of theories have been proposed to explain the evolution of this unusual pattern. However most have been difficult to test due to the fragmentary nature of the hominin fossil record and the lack of methods capable of inferring such later life history events. In search of a method we tested the hypothesis that the physiologically impactful events of parturition and menopause are recorded in dental cementum microstructure. We performed histomorphological analyses of 47 teeth from 15 individuals with known life history events and were able to detect reproductive events and menopause in all females. Furthermore, we found that other stressful events such as systemic illnesses and incarceration are also detectable. Finally, through the development of a novel analytical method we were able to time all such events with high accuracy (R-squared = 0.92).
Highlights
The life history pattern of recent humans is uniquely derived in many of its aspects including an extended post-reproductive lifespan combined with short interbirth intervals
The intercept value (y = 1.59) of the equation of the regression line reported in Fig. 2 (y = 0.94× + 1.59) indicates that there is a bias towards overestimating the age at event occurrence
In a seminal study of 223 monoradicular teeth from known-age (11 to 76 years) individuals Zander and Hürzeler[49] found that: increase in cementum thickness was near-linear; that mid-root cementum thickness best reflected age; that the slope of the regression varied by tooth type
Summary
The life history pattern of recent humans is uniquely derived in many of its aspects including an extended post-reproductive lifespan combined with short interbirth intervals. With advances in histological methods, odontochronology and skeletochronology (the study of growth layers in teeth and bones, respectively) have been increasingly applied to the study of life history evolution Mineralized tissues such as bone, enamel, dentine and cementum preserve incremental structures that are related to repeated physiological cycles[9] and can be interpreted in a similar way as tree growth rings[10]. No direct methods are available to infer age at reproductive events (RE) and length of post-reproductive lifespan (PRLS) from mineralized tissues This is because enamel and dentine formation is usually completed before these events occur, and because the remodeling activity of bone complicates the reconstruction of an individual’s chronology. Substances capable of regulating the growth of gingival fibroblasts may be released when needed and induce PDL regeneration[27]
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