Andrew Kramer

Testing for multiple species in fossil samples: an evaluation and comparison of tests for equal relative variation.

Tests for equal relative variation are valuable and frequently used tools for evaluating hypotheses about taxonomic heterogeneity in fossil hominids. In this study, Monte Carlo methods and simulated data are used to evaluate and compare 11 tests for equal relative variation. The tests evaluated include CV-based parametric bootstrap tests, modifications of Levenes test, and modified weighted scores tests. The results of these simulations show that a modified version of the weighted scores test developed by Fligner and Killeen ([1976] J. Am. Stat. Assoc. 71:210-213) is the only test that maintains an acceptable balance of type I and type II errors, even under conditions where all other tests have extraordinarily high type I error rates or little power.

Out of Africa and into the Levant: replacement or admixture in Western Asia?

Abstract Late Pleistocene Israel is the region in which issues of population mixture or competition at the time of the emergence of modern humans are most likely to be solved. For those who believe that modern humans first arose in Africa and subsequently spread throughout the world replacing archaic populations, the Levant would be the first region where such archaic populations were encountered. For those who regard the Levantine Neandertal populations as late emigres from a glaciated and inhospitable Europe, the Levant is the place where it is most likely that Neandertals encountered other human populations. If ever there was a time and place where we can examine the question of whether European and African populations exchanged ideas and mates, or competed with each other without genetic exchanges, this is it! In this paper we test the null hypothesis of a single human species occupying the Levant at the onset of the Late Pleistocene. An inability to delineate two distinct groups among the Levantine hominids would support the null hypothesis, while a demonstration of the presence of two morphs would lead to its refutation. We use non-metric traits to examine the eight most complete adult Levantine human crania to try to refute the contention first proposed by McCown and Keith (1939. The Stone Age of Mount Carmel: the Fossil Human Remains from the Levalloiso-Mousterian, Vol. II. Clarendon Press, Oxford), that the Levant “Neandertals” (Amud, Tabun) were the same species as the “early modern humans” (Qafzeh III, VI, IX; Skhul IV, V, IX). To test this hypothesis we use individual specimens as “operational taxonomic units”, and assess it using phylogenetic analysis as a heuristic clustering procedure. While our analyses produce many different trees, none of the most parsimonious ones reveal a separate Neandertal clade. Furthermore, we conducted a pairwise difference analysis of these data, which also failed to reveal a unique relationship between the Neandertal crania that would be expected if these hominids were a different species from that represented by Qafzeh and Skhul. We acknowledge that the bases for refutation are necessary but not indispensably sufficient conditions, and yet nevertheless, our findings fail to refute the null hypothesis. Instead our results suggest that the traditional “Neandertal” versus “modern human” groupings in the Levant may not be as distinct as often thought. This would imply that as populations left Africa, they interbred with the Late Pleistocene inhabitants of the Levant, and suggest that as different populations moved or expanded their range, subsequent human evolution be viewed as a consequence of the continued mixing of ideas and genes.

Effects of thermal annealing on the radiation produced electron paramagnetic resonance spectra of bovine and equine tooth enamel: Fossil and modern

The concentration of stable radiation-induced paramagnetic states in fossil teeth can be used as a measure of sample age. Temperature excursions >100 °C, however, can cause the paramagnetic state clock to differ from the actual postmortem time. We have heated irradiated enamel from both fossilized bovid and modern equine (MEQ) teeth for 30 min in 50 °C increments from 100 to 300 °C, measuring the electron paramagnetic resonance (EPR) spectrum after each anneal, to investigate such effects. Samples were irradiated again after the last anneal, with doses of 300–1200 Gy from 60Co photons, and measured. Two unirradiated MEQ samples were also annealed for 30 min at 300 °C, one in an evacuated EPR tube and the other in a tube open to the atmosphere, and subsequently irradiated. The data showed that hyperfine components attributed to the alanine radical were not detected in the irradiated MEQ sample until after the anneals. The spectrum of the MEQ sample heated in air and then irradiated was similar to that of the heat treated fossil sample. We conclude that the hyperfine components are due to sample heating to temperatures/times >100 °C/30 min and that similarities between fossil and MEQ spectra after the 300 °C/30 min MEQ anneal are also due to sample heating. We conclude that the presence of the hyperfine components in spectra of fossil tooth enamel indicate that such thermal events occurred either at the time of death, or during the postmortem history.The concentration of stable radiation-induced paramagnetic states in fossil teeth can be used as a measure of sample age. Temperature excursions >100 °C, however, can cause the paramagnetic state clock to differ from the actual postmortem time. We have heated irradiated enamel from both fossilized bovid and modern equine (MEQ) teeth for 30 min in 50 °C increments from 100 to 300 °C, measuring the electron paramagnetic resonance (EPR) spectrum after each anneal, to investigate such effects. Samples were irradiated again after the last anneal, with doses of 300–1200 Gy from 60Co photons, and measured. Two unirradiated MEQ samples were also annealed for 30 min at 300 °C, one in an evacuated EPR tube and the other in a tube open to the atmosphere, and subsequently irradiated. The data showed that hyperfine components attributed to the alanine radical were not detected in the irradiated MEQ sample until after the anneals. The spectrum of the MEQ sample heated in air and then irradiated was similar to that of t...

Brief communication: Effect of size biases in the coefficient of variation on assessing intraspecific variability in the prosimian skeleton

This study examines the effect of a measurement size bias in coefficients of variation on the evaluation of intraspecific skeletal variability in a sample of eight prosimian species (Eulemur fulvus, Hapalemur griseus, Lemur catta, Varecia variegata, Galago senegalensis, Otolemur crassicaudatus, Nycticebus coucang, and Tarsius syrichta). Measurements with smaller means were expected to have higher coefficients of variation (CVs) due to the impact of instrumental precision on the ability to assess variability. This was evaluated by testing for a negative correlation between CVs and means in the total sample, within each species, and within each measurement, and by testing for the leveraging impact of small measurements on the significance of comparisons of variability between regions of the prosimian skeleton. Three comparisons were made: cranial versus postcranial variability, epiphysis versus diaphysis variability, and forelimb versus hindlimb variability. CVs were significantly negatively correlated with means within the total sample (r(2) = 0.208, P < 0.0001) and within each species. CVs and means were significantly correlated within only three of the measurements, which may reflect the relatively low body size range of the species studied. As predicted by the higher variability of smaller measurements, removing the smallest measurements from comparisons of variable classes containing measurements of different mean magnitudes pushed the comparisons below significance. These results indicate caution should be exercised when using CVs to assess variability across sets of measurements with different means.

Paleoanthropology in the 1990s: Current foci and future directions

Jones, Steve, Robert Martin and David Pilbeam, eds. The Cambridge Encyclopedia of Human Evolution. Cambridge: Cambridge University Press, 1992. xiii + 504 pp. including appendices, further reading, and index.

Human taxonomic diversity in the pleistocene: Does Homo erectus represent multiple hominid species?

34.95 paper. Walker, Alan, and Richard Leakey, eds. The Nariokotome Homo erectus Skeleton. Cambridge, MA: Harvard University Press, 1993. 457 pp. including references and index.

Craniometric variation in large-bodied hominoids : testing the single-species hypothesis for Homo habilis

125.00 cloth.