Karen L. Baab

Research

I am a biological anthropologist who studies human evolution. My main research interests include the study of hominin (humans and the extinct relatives) taxonomy and phylogeny using cranial morphology, the application of geometric morphometrics to study skeletal variation and functional morphology, and the evolutionary history of Plio-Pleistocene Homo.

I am currently an Associate Professor in the Department of Anatomy at Midwestern University in Glendale, AZ. After earning my Ph.D. in anthropology at the City University of New York (part of the New York Consortium in Evolutionary Primatology) in 2007, I was a Research Instructor in the Department of Anatomical Sciences at Stony Brook University and then an Assistant Professor in the Department of Anthropology at the same university.

Click here for CV (updated 1/2022).

RECENT STUDIES

I recently completed a virtual reconstruction of the BSN12 hominin fossil from Gona, Ethiopia in collaboration with members of the Gona Paleoanthropological Research Project. BSN12, dated to 1.26 million years ago, along with the more complete DAN5 skull dated to 1.55 million years ago (Ma) are two crania from Gona assigned to Homo erectus and first described in 2020. In a recent paper published in the Journal of Human Evolution, we used a comparative study with a large sample (n=38) of Homo erectus to demonstrate that some of the difference in endocranial volume between the two Gona fossils reflects broader species-level brain expansion from 1.77 to 0.1 Ma. The BSN12 partial cranium is markedly larger than the DAN5 skull (598 cm3), but both fossils represent the smallest adult Homo erectus known from their respective time periods in Africa. Although the DAN5 cranium bears a particularly close affinity to the Georgian Homo erectus fossils at Dmanisi and to Kenyan fossils assigned to Homo habilis, the study confirmed that the DAN5 fossil is likely early African Homo erectus, though the smallest yet found in Africa. The earlier study attributed the differences in size and robusticity of the two fossils to either sexual dimorphism or anagenetic evolution. The current study concludes that no clear pattern of sexually patterned size or shape differences are shown within Homo erectus based on current assessments of sex for individual fossils

Figure 2: The fragments and reconstruction of the BSN12/P1 calvaria fossil. The fragments consist of A) most of the left parietal (superior view) B) supero-medial portion of the left frontal squama (superior view), C) parts of the right frontal and parietal bones (lateral view), and D) right lateral supraorbital torus and orbit wall (anterior oblique view). Pieces from the right vault (C, D) were reflected to the left. Features used to position the fragments are highlighted: coronal suture (gray arrow), bregma (white arrow) and temporal line (red arrow). The R2 reconstruction is shown in E) lateral, F) superior and G) anterior views using surface renderings with colors colored by fragment (top) and in gray (bottom). In F, the left frontal fragment is shown in semi-transparent blue to help visualize overlap between this piece and the left lateral vault piece (aqua). H shows the three realistic reconstructions based on different positions of the fragment shown in D. The position of the supraorbital fragment in reconstruction R1 is shown in aqua, R2 in purple and R3 in chartreuse.

Ongoing Projects

Homo erectus Systematics and Evolutionary History

I have a longstanding interest in the widespread and long-lived human ancestor known as Homo erectus. The oldest fossil humans outside of African (at Dmanisi, Georgia) are attributed to H. erectus and members of this species are found as far south as South Africa and as far east as China and Indonesia. My work focuses on quantifying the shape of the skull in members of this group in order to better understand whether this is in fact a single species (versus multiple species), the relationships among populations, and the factors that have influenced differences in cranial shape across this species range.

Evolutionary Quantitative Genetics Applied to Hominins

My interest in evolution and population history are a natural fit for quantitative genetic approaches, a set of methods designed for studying complex traits under polygenic inheritance. These population genetics methods have been adapted for morphological traits, such as the shape of the skull. I have several ongoing projects that seek to reveal aspects of population history in early and later Homo evolution, including an NSF-funded project that links chewing biomechanics, skeletal morphology and evolutionary history.

Homo floresiensis Systematics and Evolutionary History

I have also led a series of studies of the famous "Hobbits" of Flores, Indonesia.This work compared the shape of the LB1 skull to a large comparative sample of modern humans (including small bodied populations), fossil hominins, and apes. These analyses explicitly consider the scaling relationship between size and shape. More recent analyses have re-evaluated claims that these fossils are actually small-bodied modern humans, with the most complete individual (LB1) suffering from a pathological condition. My results consistently support the hypothesis that Homo floresiensis is a late-surviving species whose strongest affinities lie with early Homo.

Homo erectus cranial development

Previous studies demonstrated that Homo erectus growth and development is intermediate in its mode and tempo between recent humans and chimpanzees. We are using these close relatives of Homo erectus to model shape changes to the braincase from infancy to adulthood. The results of this study suggest that if Homo erectus development occurred more along the lines of chimpanzees than recent humans. Moreover, a key subadult fossil from 1.5 million years ago (KNM-ER 42700) assigned to Homo erectus is somewhat of an outlier and particularly if development occurred along a more human-like path.

Map of possible Homo erectus sites and hypothetical directions of migration and/or gene flow.

Homo species means and the ancestral node reconstructions plotted in the space with within-population variation. (From Baab, 2018)

Line drawing of LB1 fossil (type specimen of Homo floresiensis) with 3D landmarks superimposed (blue).

Representatives 3D models of chimpanzees (top), recent humans (middle) and Homo erectus (bottom) from juvenile (left) to adult (right).

Recent Peer Reviewed Publications
(most are available on ResearchGate)

Bruner, E., Halloway, R., Baab, K.L., Rogers, M.J., Semaw, S. (2023) The endocast from Dana Aoule North (DAN5/P!): A 1.5 million year-old human braincase from Gona, Afar, Ethiopia. American Journal of Biological Anthropology. 181: 206-215.

Riede, T., Stein, A., Baab, K.L., Hoxworth, J.M. (2023) Post-pubertal developmental trajectories of laryngeal shape and size in humans. Scientific Reports. 13: 7673.

Ward, D. L., Schroeder, L., Roy, J. E., Hertz, M., Uhl, A., Pomeroy, E., Stock, J. T., Copes, L., Baab, K. L., Viola, T. B., Silcox, M. T. (2022) The influence of subsistence strategy and climate on bony labyrinth morphology in recent Homo sapiens. American Journal of Biological Anthropology, 177: 454-470.

Baab, K.L., Rogers, M., Bruner, E., Semaw, S. (2022) Reconstruction and analysis of the DAN5/P1 and BSN12/P1 Gona early Pleistocene Homo fossils. Journal of Human Evolution. 162: 103102.

Baab, K.L., Nesbitt, A., Hublin, J.-J., Neubauer, S. (2021) Assessing the status of the KNM-ER 42700 fossil using Homo erectus neurocranial development. Journal of Human Evolution. 154: 102980.

Baab, K.L. (2021) Reconstructing cranial evolution in an extinct hominin. Proceedings of the Royal Society B. 288: 20202604. Pdf

Riede, T., Coyne, M., Tafoya, B., Baab, K.L. (2020) Postnatal development of the mouse larynx: negative allometry, age-dependent shape changes, morphological integration, and a size-dependent spectral feature. Journal of Speech, Language, and Hearing Research. 63: 2680-94.

Borgard, H.L., Baab, K., Pasch, B. and Riede, T., (2020) The shape of sound: a geometric morphometrics approach to laryngeal functional morphology. Journal of Mammalian Evolution, 27: 577-590.

Baab, K.L. (2018) Evolvability and craniofacial diversification in genus Homo. Evolution. 72: 2781-2791.

Zichello, J., Baab, K.L., McNulty, K.P., Raxworthy, C.J. and Steiper, M.E. (2018) Hominoid intraspcific cranial variation mirrors nuetral genetic diversity. Proceedings of the National Academy of Sciences. 115: 11501-11506.

Baab, K.L., Copes, L.E., Ward, D., Wells, N., Grine, F.E. (2018) Using modern human cortical bone distribution to test the systemic robusticity hypothesis. Journal of Human Evolution. 119: 64-82.

Baab, K.L. and Zaim, Y. (2017) Global and local perspectives on cranial shape variation in Indonesian Homo erectus. Anthrpological Science. 125: 67-83.

Baab, K.L. (2016) The role of neurocranial shape in defining the boundaries of an expanded Homo erectus hypodigm. Journal of Human Evolution. 92: 1-21.

Baab K.L., Brown P., Falk D., Richtsmeier J.T., Hildebolt C.F., Smith K., Jungers W. (2016) A critical evaluation of the Down syndrome diagnosis for LB1, type specimen of Homo floresiensis. PLoS ONE. 11(6): e0155731

Baab, K.L. (2016) The place of Homo floresiensis in human evolution. Journal of Anthropological Sciences. 94: Early View. Link to pdf.

Baab, K.L. (2015) Defining Homo erectus. Henke, W. and Tattersall, I. (Eds.). Handbook of Paleoanthropology. New York: Springer, pp. 2189-2219. *Invited*

Baab, K.L.(2014) Phylogenetic, ecological, and allometric correlates of cranial shape in Malagasy lemuriforms. Evolution. 68: 1450–1468.

Baab, K.L., McNulty, K.P., and Harvati, K. 2013. Homo floresiensis contextualized: A geometric morphometric comparative analysis of fossil and pathological human samples. PLoS ONE. 8(7): e69119.

Baab, K.L., McNulty, K.P., and Rohlf, F.J. 2012. The shape of human evolution: A geometric morphometrics perspective. Evolutionary Anthropology. 21: 151-165.

McNulty, K.P. and Baab, K.L. 2010. Keeping asymmetry in perspective: A reply to Eckhardt and Henneberg. American Journal of Physical Anthropology. 143: 337-339.

Baab, K.L., Freidline, S.E., Wang, S.L., and Hanson, T. 2010. Relationship of cranial robusticity to cranial form, geography and climate in Homo sapiens. American Journal of Physical Anthropology. 141: 97-115.

Baab, K.L. and McNulty, K.P. 2009. Size, shape, and asymmetry in fossil hominins: The status of the LB1 cranium based on 3D morphometric analyses. Journal of Human Evolution. 57: 608-622.

Baab, K.L. 2008. The taxonomic implications of cranial shape variation in Homo erectus. Journal of Human Evolution. 54: 827-847.

Baab, K.L. 2008. A re-evaluation of the taxonomic affinities of the early Homo cranium KNM-ER 42700. Journal of Human Evolution. 55: 741-746.

EVOLUTION SOUP INTERVIEWS

Popular Media Coverage of "Hobbit" Studies

2023: Article on Ancient Origins website Link to article.

2020 YouTube "Evolution Soup" Interview (see video above)

2014 Public Lecture in Erice, Italy:
Interviewed for Italian science website Pikaia. Link to interview (in Italian).

2013:
Featured in the New York Times. Link to article.
Author spotlight blog post on PLoS ONE. Link to blog.
Featured in Le Monde (Paris). Link to article.
Featured in Newsday (Long Island). Download article.
Featured on Planeterde.de. Link to article.
Featured on ATSE Wonder of Science. Link to article.
Featured in Zero Hora (Brazil). Link to article.

2009:
The American Museum of Natural History did a Human Bulletin piece that featured our research and a video is currently featured in the Hall of Human Origins (through Feb. 6, 2009). Navigate directly to the AMNH webpage.

Several on-line news outlets also covered this story, including USA Today, National Geographic, the Guardian (UK), and ScienceDaily. Elizabeth Culotta also mentions the Significance piece in the Science "Origins" blog.

Current Courses
(Midwestern University, Department of Anatomy)

ANAT 503, BASI 1509, ANATG1551/1552/1553