American Journal of Primatology 15:17-29 (1988) Dental Eruption Schedules of Wild and Captive Baboons JANE E. PHILLIPS-CONROY’ AND CLIFFORD J. JOLLY2 ‘Department of Anatomy and Neurobiology, Washington University School of Medicine, and Department of Anthropology, Washington University, and ‘Department of Anthropology, New York University Dental eruption schedules previously used to age wild baboons have in the past derived from studies of captive animals housed under standard conditions and fed standard laboratory diets. This paper reports for the first time eruption schedules derived from wild baboons, the yellow baboons (Papio hamadryas cynocephalus) of Mikumi National Park, Tanzania, and compares these schedules with those of other baboon subspecies inhabiting both similar and dissimilar environments. Eighteen males and twelve females from the Viramba groups, ranging in age from 21 to 103 months, were trapped, and dental impressions and notes were made of the state of eruption of each tooth. Eruption of all teeth were delayed a t Mikumi relative to the baboon standards derived from the captive animals at the Southwest Foundation for Biomedical Research, San Antonio, Texas. Teeth of the canine-premolar 3 complex and third molars were most delayed, erupting up to a year and a half later than their counterparts from captive animals. Comparison with data on hamadryas baboons from Erer-Gota in Ethiopia revealed that both the hamadryas and yellow subspecies of baboons, with different genetic backgrounds and living under markedly different environmental conditions, followed the same schedule. This constancy of developmental schedules suggests that these Mikumi data may reasonably be used as standards for other wild baboon populations and that acceleration of dental maturation, as well as maturation of other somatic systems in captivity, is another manifestation of the short-term adaptive plasticity of the baboon species as a whole. Key words: baboons, captive-wild contrasts, dentition, maturation, Mikumi INTRODUCTION Dental eruption is a convenient index of maturation, easily assessed by simple, noninvasive techniques, and, supposedly, “relatively impervious t o environmental factors” [Demirjian, 1986:2951. In primatology, its applications have included determining the age of wild-caught animals, developing growth curves for different elements of the skeleton where age is used as the independent variable, and Received August 3, 1987; revision accepted January 15, 1988. Address reprint requests to Dr. Jane E. Phillips-Conroy, Department of Anatomy and Neurobiology, Washington University School of Medicine, 660 S. Euelid Avenue, St. Louis, MO 63110. 0 1988 Alan R. Liss, Inc. 18 I Phillips-Conroy and Jolly comparing such velocity curves from different populations. The most extensive studies concern rhesus monkeys (Macaca mulatta) and baboons (Papio hamudryas sensu lato, [Groves, in Thorington and Groves, 19703) species readily available in captive colonies. These studies have confirmed the usefulness of dental criteria as indicators of chronological age, apart from a few long intervals when no tooth is erupting. Dental eruption interested us principally as a means of using mixed longitudinal data to estimate demographic parameters and the dynamics of gene flow in wild populations. With continuous, long-term observation, as in the studies of yellow baboons (Papio hamadryas cynocephatus) at Amboseli [Altmann et al., 19811and Mikumi [Rhine, 19861 and in studies of toque macaques [Macacasinical in Sri Lanka [Dittus, 19751, individual ages can be directly ascertained. Lacking longitudinal data, one can estimate the age of both immature and mature animals by using dental wear as well as eruption [Phillips-Conroy, 19781. The estimation procedure has two major requirements; a sample of immature animals representing all eruption stages, and a reliable schedule relating eruption to chronological age. In a study of age structure and phenotypic variability in the Awash hybrid baboon zone as it existed in 1973 [Phillips-Conroy and Jolly, 19861, we based age estimates on an extensive collection of dental casts taken from the population by the 1973 expedition and on an eruption schedule derived from longitudinal observations upon a small number of yellow baboons (Papio hamadryas cynocephalus) of southern Kenyan ancestry, born and raised at the Southwest Foundation for Research and Education (SWFRE) [now the Southwest Foundation for Biomedical Research], San Antonio, Texas [Reed 1965, 1967, 1973, and R. G. Cauble personal communication). That this sample of captive yellow baboons accurately represented dental eruption in wild baboons of other subspecies remained an untested assumption. More recently, Sigg et al. [19821observed tooth eruption in wild hamadryas baboons (P. h. hamadryas) of known age and found it to be delayed relative to the SWFRE schedule. Similar data from Tanzanian yellow baboons are reported here. Although the new data sets fall far short of the large samples that have been used to elucidate the details of dental maturation in human populations [Gates, 19661, they do allow a broad comparison of Reed’s schedules with those seen in wild baboons of two different subspecies. MATERIALS AND METHODS Reed’s schedules were based upon monthly radiographs of “over 20” SWFRE animals, which together documented dental eruption from 16 months to the appearance of the last tooth, the third molar. Eruption is defined as the first penetration of the gum by the tooth. In his latest publication, Reed  gave a mean age a t eruption for all permanent teeth, and in the unpublished tables used by Cauble (personal communication), the data for the two sexes were separated (Table I). The hamadryas baboons discussed by Sigg et al. [19821 were trapped from groups observed for about 5.5 years, living at Erer-Gota, Ethiopia. The sample included 13 males and 27 females ranging in age from 6 to 78 months. The dates of birth of younger animals were known; those of animals older than 66 months presumably were estimated from the appearance of the individual a t the start of the observation period. Sigg and coworkers assigned each animal a dental score [Snow, 19671 indicating the total number of teeth that had erupted, deciduous or permanent. For example, an infant with deciduous teeth plus first permanent molars scored 24, while an adult had a score of 52, representing 20 deciduous teeth (now replaced) and 32 permanent. Dental Eruption in Baboons / 19 TABLE I. Mean Eruption Ages (SWFRE) and Estimated Median Eruption Ages (MIK, Mikumi) of Permanent Teeth, in Months, Rounded to Whole Month MIK-SWFRE SWFRE Male Lower I1 I2 C P3 P4 M1 M2 M3 Upper I1 I2 35 39 54 54 52 19 46 75 MIK Male 41 52 68 68 64 25 52 77 35 44 39 52 C 57 76 P3 50 52 P4 52 64 M1 23 25 M2 47 57 M3 80 98 (Upper+ lower)/2 (excluding P3) I1 35.0 42.5 I2 39.0 52.0 C 55.5 72.0 P4 52.0 64.0 M1 21.0 25.0 M2 46.5 54.5 M3 77.5 87.5 SWFRE Female MIK Female Male Female 34 37 47 47 52 21 45 74 41 50 55 60 63 50 92 6 13 14 14 12 6 6 2 7 13 8 13 11 5 18 35 39 9 13 19 50 52 24 47 85 41 50 55 56 60 50 92 6 11 6 6 8 34.5 38.0 48.0 52.0 22.5 46.0 79.5 41.0 50.0 55.0 62.0 50.0 92.0 7.5 13.0 16.5 12.0 4.0 8.0 10.0 49 2 10 2 10 18 3 7 6.5 12.0 7 .O 10.0 4.0 12.5 The sample of Tanzanian yellow baboons was drawn from populations living in the Mikumi National Park, Tanzania. The sample included 18 males and 13 females of known age, trapped in groups known as Viramba 1 and Viramba 2, drawn from a total of 151 animals trapped by Jeffrey Rogers and ourselves between July 1985 and August 1986. Ages ranged from 21 to 102 months; in all cases the date of birth was known within several days (R. Rhine and S. Wasser, personal communication). Animals were caught in baited cages and tranquilized, or subdued with a tranquilizer dart, as described elsewhere [Brett et al., 1982; Phillips-Conroy et al., 19871. Each tooth's state of eruption was determined by inspection and recorded. Differences among the data sets to some extent limit the comparisons that can be made and must be considered in their interpretation. Instead of complete dental records, Sigg et al. 119821provide a diagram showing dental scores, thus precluding use of their data to compare the sequence and timing of eruption of particular teeth. When comparing SWFRE and Mikumi, one must take into account the mode of data collection. Reed's observations were longitudinal, so that the age of eruption of a tooth is in error at most by the month's interval between examinations. Unfortunately, Reed cites only mean eruption ages and some ranges, not individual values, or estimates of variation, as is desirable when using a sample to estimate the values of a population [Caughley, 19771. Mikumi records are cross-sectional and permit accurate estimation of the age of eruption of a particular 20 / Phillips-Conroy and Jolly tooth only in cases where it was caught in the act of breaking through the gum. Other cases, where the tooth is fully erupted, or the gum is unbroken, provide only a terminus ante or post quem for eruption events in that individual. A “median age of eruption” was estimated for the population by finding the oldest animal of an unbroken series lacking the tooth in question and the youngest animal of an unbroken series in which the tooth had erupted, and then taking the midpoint between them (see Fig. 1). To illustrate: in Figure 1the central upper incisor in males first makes its appearance in a 46-month-old individual, is not yet erupted in a 51-month-old individual but is present in all individuals 52 months and older. The median age of eruption therefore lies at 44 months-halfway between 35 months and 52 months. Although this method estimates the halfway point of the eruption interval as well as other methods, it is subject to errors of estimate due to individual variation [Bailit, 19761and is also subject to inaccuracies arising from incomplete coverage. A wide array of ages is represented in the Mikumi sample, but as Figure 1shows, some age intervals are undocumented. Eruption events falling in the wider gaps are less precisely estimated. For example, no male falls in the period between 35 and 46 months, when the central incisors erupt. The estimated median age of 40.5 months (rounded to 41) for this event is clearly a rough approximation. This is also the case for the upper M2, which erupts between 52 and 62 months, thereby having a median eruption age of 57. The estimates for the other male teeth are closely defined by observed cases. Among females, the least reliable estimates are for lower P4 and the third molars. Because of the dissimilar nature of the data sets, the comparison was carried out in two stages, using slightly different procedures: First the timing and sequence of eruption in the SWFRE and Mikumi yellow baboons was compared. The relation of dental score to age was then compared in all three populations. RESULTS Figure 1 shows the eruption state of each tooth in the Mikumi sample and estimated median eruption ages in either sex. In Figure 2, these values are plotted against the mean eruption ages of the SWFRE sample. These values, and the differences between them, are shown in Table I. Although the eruption sequence was similar in the two populations, Mikumi median eruption age for every tooth exceeded the corresponding SWFRE mean eruption age. Assuming that median and mean eruption ages are close in these populations (as seems to be true of large human samples [Hayes and Mantel, 1958; Gates, 1966]),such consistency suggests a real, biologically meaningful difference, even though these data did not allow determination of the statistical significance of the difference between populations for each individual tooth. Some of the median eruption age estimates based on the Mikumi sample were more reliable than others. Luckily, some of those (such as I2 and lower P3 in females) that were most different were among the most tightly defined estimates. Another contrast seen in Figure 2 was the greater tendency for Mikumi values to cluster, for example, estimates for both I2 and both M2 of Fig. 1. Timing of eruption of Mikumi baboon dentition. Each circle represents an individual of known age positioned on the scale that represents months of age. For each tooth, males are above the line and females below. Upper and lower teeth are treated separately except for first molars and lateral incisors since the timing of eruption in these teeth did not vary. Open circles represent individuals in whom that tooth is not yet erupted; filled circles represent erupted teeth. The arrows represent median time to eruption, as given in Table I. !: . * 1 e e I/ 0 0 0 0 22 I Phillips-Conroy and Jolly females lay at 50 months. This was certainly an artifact of the method of estimation and of small sample size and had no biological significance. A more fine-grained record would very probably have shown each lower incisor and molar leading its upper equivalent, as in the Reed series and in other monkey species [Schultz, 19351. Since Reed’s schedule had been used to age Ethiopian baboons [Phillips-Conroy and Jolly, 19861, this procedure was checked by estimating the ages of Mikumi known-age baboons according to Reed‘s criteria and plotting these estimates against actual ages (Fig. 3). As expected, there was a high correlation between the two ages (r = .96 for males; r = .90 for females, P < 0.0001 and P< .001, respectively). More significantly, the Reed schedule underestimated the real age of all animals but one, as can be seen by the location of points to the right of the line of equivalence. DISCUSSION Whereas the overall acceleration of dental eruption in the captive population was unequivocal, the degree of acceleration characteristic of particular teeth was less certain, such estimates being especially liable to the biasing effect of small sample sizes and inter-individual variability. The following apparent patterns are given here with the caveat that larger samples may well prove some of them to be illusory. First, there was a tendency for the later erupting teeth to show a greater discrepancy between the two populations. Presumably, there are developmental constraints linking the eruption of successive teeth, so that such a cumulative effect was not surprising. Perhaps more interesting and significant was the extent to which acceleration differed in teeth of the two major dental complexes (Table 11). In cercopithecines, the upper and lower canines and the anterior lower premolar comprise a complex whose primary function is fighting and threat rather than feeding. These teeth are not only functionally linked, they are also distinguished from the rest of the dentition in that they show large sex differences in shape, size, and the timing of their eruption [Phillips-Conroy and Jolly, 19811. The relatively late eruption of the “agonistic” cluster in males (Fig. 2) accounted for the sex difference in eruption sequence seen in both wild and captive baboons and in rhesus monkeys [Schultz, 19351. Considering first the “eating teeth,” intervals in this series (birth-11, 11-12) ranged from 7.5 to 5.5 months shorter in the captive group than in the wild groups (average abbreviation, 6.5 months). In the molar series (birth-M1, Ml-M2, and M2-M3) captive groups averaged 4.6 months shorter than the wild groups, with a range of 2.5 to 8.5 (the outlier here was the M2-M3 interval in females, which was affected by the apparently late eruption of female third molars at Mikumi). By comparison, the “agonistic” teeth appeared more accelerated, especially in males. The interval between birth and the eruption of each of the teeth of the canine-P3 cluster was shortened by at least a year in captive males; the upper canine was the most extreme, erupting nearly 1.5 years earlier. As Figure 2 shows, the outcome was a change in the relative timing of canine-P3 and molar eruption. Although its position in the sequence was unchanged, in captive males the canine cluster erupted about one third of the way into the long M2-M3 interval rather than about halfway through it, and the canine to M3 interval, in fact, was actually absolutely longer. Captive females showed a less marked effect; eruption of the canine cluster was brought forward to a point very close to the start of the M2-M3 interval. The canine-M3 interval shortened appreciably, however, rather than lengthening as in males. To compare the Mikumi and SWFRE samples with the hamadryas from Dental Eruption in Baboons I 23 Erer-Gota, the yellow baboon data were changed into dental scores and were compared with the dental scores from the hamadryas baboons and the SWFRE baboons, both of which were published in diagrammatic form by Sigg et al. . Figure 4 shows curves representing dental scores in the two wild and one captive sample plotted against age. Unfortunately, no females in the sample from Erer-Gota were between 4.5 and 6 years old, and no males were older than 5 but younger than the age a t which all third molars are erupted, represented on the graph as greater than 96 months (8 years). Nevertheless, the general picture was clear. The curves representing the two wild populations are practically coincident and cross over, indicating no consistent difference between them. The Erer-Gota hamadryas baboons and the Mikumi yellow baboons were apparently equally delayed relative to the captive SWFRE animals. Results based on comparatively small samples obviously must be treated with caution, but the following major conclusions are offered with confidence: First, the two wild populations did not differ detectably. Second, eruption was generally accelerated in captivity, the eruption of particular teeth occurring from 2 to 19 months earlier in captive baboons. There was also a strong indication that this acceleration most markedly affected the male canine-P3 complex. Although the dentition of wild baboons of known age has not been previously systematically examined, some published observations suggest that the teeth, at least the easily observed male upper canine, are late-erupting in other wild populations. Altmann et al. [19811 note that in yellow baboons at Amboseli the male canine was seen to project beyond the occlusal plane between 5 and 6 years of age. Packer [19791 observed canine eruption between 5.5 and 6 years in male olive baboons (P. h. anubis) a t Gombe, Tanzania. The maturation of other systems was also more or less synchronous in all wild baboons reported. For example, menarche occurs a t 4.5-5.6 years in olive baboons at Gombe [Packer, 19791, a t 4-5.5 years in yellow baboons at Amboseli [Altmann et al., 19811, and a t 4.3-5.6 years in hamadryas baboons at Erer-Gota [Sigg et al., 19821. The constancy of developmental schedules in wild baboon populations is perhaps unexpected in view of their dissimilar habitats. Mikumi, for instance, is woodland savanna with an annual rainfall averaging 842 mm. It is transected by the Mkata River and its floodplain. Bruchystegia woodland covers the hills, with dense thickets and patches of forest on the upper hill slopes. Norton et al. [19871 estimate that of the 700 to 800 plant species in the Park, about 180 are eaten by baboons. The Erer-Gota baboons, however, live in Acacia thornscrub with a mean yearly rainfall of only 600 mm [Kummer et al., 19811. In the Awash National Park, a similar semi-arid thorn scrub supports less than half as many plant species as Mikumi. At first sight, then, the comparison between Mikumi and Erer-Gota seems to bear upon Popp’s [19831 hypothesis that “Populations of well fed baboons should contain individuals who have high rates of reproduction but shortened life spans and populations of poorly fed baboons should have low rates of reproduction but extended life spans’’ [Popp, 1983:1991. Popp’s argument would predict faster maturation in the “lusher” habitat of Mikumi. That this expectation is evidently not borne out by observation can be variously explained. Most likely the relative “lushness” of habitats like Mikumi is more apparent than real, when considered from the perspective of the individual baboon. Resources at Erer-Gota are certainly more sparse, but so are baboons, and competing species are fewer. There is no evidence that Mikumi baboons as individuals have a higher or more reliable caloric intake as a result of their “lusher” habitat, or that they are in fact better nourished. Indeed, no subcutaneous fat deposits were detected by calliper in either Mikumi or Awash baboons (Phillips-Conroy and Jolly, unpublished observations) 4 m Dental Eruption in Baboons / 25 UQT Q H=O. - -0. as6996 675666*x + 9 . 9 a 4 a i 3 100%1ine o f equivalence lo 10 10 ,a 50 6 0 ?O 80 90 loo I ,I0 R e a l ages (months) Fig. 3. Real ages plotted against Reed‘s ages. X axis represents real ages of known Mikumi animals. Y values are ages as estimated from Reed’s eruption criteria for the SWFRE baboons. and resource competition lowered survivorship when Viramba infants were born into a many-membered cohort [Wasser and Starling, 19861. Alternatively, individual Mikumi baboons may indeed have access to additional calories, but they may “choose” to spend them in other energy-consuming but fitness-enhancing activities, such as intra-group competition. This prediction of Popp’s model is by no means excluded by these findings, nor, of course, is the possibility that other aspects of developmental scheduling will be found to differ in yellow and hamadryas baboons. Finally, the dental eruption schedule is obviously the outcome of a complex genetic-environmental interaction [cf. Bailey and Garn, 19861. Finding apparently similar schedules does not exclude the possibility that neither genetic nor environmental factors are identical in the two populations, but that the genome of each population is adapted to produce the standard maturation schedule under local conditions. Rather elaborate experiments would be required to test this possibility. Whatever its explanation, the apparent constancy of dental scheduling in wild populations is gratifying in that it suggests that eruption schedules derived from one wild population of Papio hamadryas may be judiciously used to estimate the ages of animals from another such population, even if ecological circumstances and Fig. 2. A comparison of Reed’s mean eruption times with Mikumi median eruption times. Individual teeth are positioned on this scale which represents age in months according to their median (Mikumi)and mean (SWFRE) eruption times (see Table I). (A) SWFRE males. (B) Mikumi males. (C) SWFRE females. (D) Mikumi females Dotted lines connecting the SWFRE mean times with the Mikumi median times indicate by their slope the relative degree of acceleration of the captive animals. 26 / Phillips-Conroy and Jolly TABLE 11. Intervals Between Eruption Ages of Various Teeth* Interval MIK-SWFRE SWFRE Male MIK Male SWFRE Female MIK Female Male Female Molar Series Birth to M1 MI to M2 M2 to M3 Incisor series Birth to I1 I1 to I2 Canine cluster Birth to C Birth to Lwr P3 Lwr C to Upr C Canine cluster relative C to M3 Lwr P3 to M3 21.0 25.5 31.0 25.0 29.5 33.5 22.5 23.5 33.5 L27.01 L23.01 42.0 4.0 4.0 2.5 L4.51 L4.01 8.5 35.0 4.0 42.5 9.5 34.5 3.5 41.0 9.0 7.5 5.5 6.5 5.5 72.0 68.0 8.0 48.0 47.0 2.0 55.0 60.0 0.0 16.5 14.0 5.0 7.0 13.0 2.0 15.5 19.5 31.5 32.5 37.0 32.0 -6.5 -4.0 5.5 -.5 55.5 54.0 3.0 to molars 22.0 23.5 *Unless otherwise indicated, intervals were determined from averaged upper and lower eruption ages. Bracketed, MIK female M1 eruption age estimated from MIK male and SWFRE values, and intervals derived therefrom. subspecific affiliation are different. This study also shows, as previous work [Sigg et al., 1982; Altmann et al., 19811suggested, that developmental schedules derived from captive baboons are likely to result in systematic errors if applied to wild-caught animals. All ages of wild-caught animals would tend to be underestimated, and the error would be compounded as age increases. Ages that have been estimated this way in the past should be revised by reference to the best estimates of "wild" eruption ages. The median eruption ages presented here are not claimed to be definitive. Although systematic error due to the influence of captivity was eliminated, errors may have been introduced by sampling bias in the age distribution of subjects and the random idiosyncrasies of individuals as well as possible population-specific differences too subtle to have been detected here. More and larger samples of known-age7 wild-caught animals are obviously needed to validate the estimates. The Mikumi-SWFRE contrast indicates that dental eruption schedules are developmentally plastic. Genetic factors probably can be ruled out because the two samples were of the same subspecies and were of closely adjacent geographical origin. However, the causes of abnormally fast dental eruption in the captive group are not immediately obvious; however, tooth eruption seems to be but one aspect of a general developmental acceleration in captive baboons. Menarche, for example, is attained a t about 3 years in the SWFRE population, 1.5years earlier than in the wild [Altmann et al., 19811. Diet might well be implicated, because captive baboons are routinely maintained on generous quantities of a high-calorie, high-protein, vitamin-supplemented diet [Kalter, 19731. Published information is equivocal on the capacity of diet to retard or accelerate human dental eruption. While some studies found slower dental development associated with malnutrition [El Lozy et al., 19751, poverty [Garn et al., 19731, or poor prenatal nutrition [Delgado et al., 19751, others [cited by Demirjian, 19861 failed to show such a relationship. A general finding is that by the time protein calorie malnutrition is severe enough to delay dental emergence, it has already produced very obvious pathological effects upon other Dental Eruption in Baboons / 27 I#-- 0 0 Age (months) Fig. 4. Comparison of curves of dental score against age for the SWFRE captive baboons and the wild baboons of Erer-Gota and Mikumi. Solid line represents SWFRE curve. Dashed line is Erer-Gob curve. Starred line is Mikumi curve. The lines are calculated by plotting the mean age of animals at a given dental score. SWFm and Erer-Gota lines are derived from Sigg e t al., 1982. aspects of growth such as weight and stature. Moreover, it seems unhelpful to interpret all known populations of wild baboons as suffering from severe, general malnutrition. On the other hand, the laboratory regime might well be considered abnormal, in that it leads to over-nutrition by comparison with the natural setting and laboratory animals on maintenance diet regularly carry subcutaneous fat [Coelho, 19851at levels exceeding that found in wild animals [Phillips-Conroy and Jolly, unpublished data). In any event, it may be misleading to discuss the effects of captivity on dental eruption solely in terms of proximate causes and pathology, regarding the wild or the captive population as subject to “abnormal” conditions. As Hrdy has argued, appeals to “abnormality” or “pathology” as explanations can obfuscate the search for ultimate causes and selective effects. In the present case, it may be more worthwhile to consider developmental plasticity itself as an adaptive feature of the species. What selective forces might lead to the evolution of such a capacity? Why does it take a particular form, and why is it elicited by conditions in captivity? That the answer may lie in the selective effects upon population structure produced by environments that are subject to unpredictable, decade-long, perturbations in productivity [Bradley et al., 19871 is a possibility to be pursued elsewhere. CONCLUSIONS 1. Dental eruption schedules of hamadryas baboons a t Erer-Gota, Ethiopia, and yellow baboons a t Mikumi, Tanzania, did not detectably differ. 28 I Phillips-Conroy and Jolly 2. Dental eruption was accelerated in captivity relative to wild populations, with median times of eruption occurring 2 to 19 months earlier in captive than in wild baboons. 3. Accelerated eruption in captive relative to wild baboons was most pronounced in the male canine-P3 complex. ACKNOWLEDGMENTS We thank the Tanzanian National Scientific Research Organisation and Serengeti Research Institute for permission to conduct our research at Mikumi National Park, and Mikumi Senior Park Wardens Mr. Kishe and Mr. Kibasa for facilitating our research there. These data were collected by Jeffrey Rogers and J.E.P.-C. with the collaboration of R. Rhine, G. Norton, and S. Wasser of the Animal Behavior Research Unit of Mikumi National Park, who additionally made available all facilities of that research station. We thank E. Sterling, C. Fimbel, D. Wilson, M. Liebman, L. Weitkamp, and the Mikumi game scouts for their enthusiastic and capable assistance. Funding for this project was provided by NSF grant BNS83-03506. REFERENCES Altmann, J.; Altmann, S.A.; Hausfater, G. Physical maturation and age estimates of yellow baboons, Papio cynocephalus, in Amboseli National Park, Kenya. AMERICAN JOURNAL OF PRIMATOLOGY 1:389-399, 1981. Bailey, S.M.; Garn, S.M. The genetics of maturation. 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