STRUCTURE OF MATERIALS

134 ESRF

Australopithecus afarensis endocasts suggest ape-like brain organization and prolonged brain growth, P. Gunz (a), S. Neubauer (a), D. Falk (b,c), P. Tafforeau (d), A. Le Cabec (a,d), T.M. Smith (e), W.H. Kimbel (f), F. Spoor (a,g,h) and Z. Alemseged (i), Sci. Adv. 6(14), eaaz4729 (2020); https://doi.org/10.1126/sciadv.aaz4729. (a) Department of Human Evolution,

Max Planck Institute for Evolutionary Anthropology Leipzig (Germany) (b) Department of Anthropology, Florida State University (USA) (c) School for Advanced Research, Santa Fe (USA) (d) ESRF (e) Australian Research Centre for Human Evolution, Griffith University (Australia) (f) Institute of Human Origins, and School

of Human Evolution and Social Change, Arizona State University (USA) (g) Centre for Human Evolution Research, Department of Earth Sciences, Natural History Museum (UK) (h) Department of Anthropology, UCL (UK) (i) Department of Organismal Biology and Anatomy, University of Chicago (USA)

[1] A. Le Cabec et al., PLoS One 10 (2015). [2] Z. Alemseged et al., Nature 443, 296-301 (2006). [3] K. J. Carlson et al., Science 333, 1402-1407 (2011).

PRINCIPAL PUBLICATION AND AUTHORS

REFERENCES

previously undetected endocranial features. These data shed new light on two questions that have been controversial: Is there evidence for human-like brain reorganisation in A. afarensis? Was the pattern of brain growth in A. afarensis more similar to that of chimpanzees or that of humans?

Scans of the Dikika child s dentition (Figure 117) made it possible to determine the exact age at death by counting incremental growth lines: 861 days (2.4 years). The pace of dental development of the Dikika infant was broadly comparable to that of chimpanzees and therefore faster than in modern humans. However, given that the brains of A. afarensis adults were roughly 20% larger than those of chimpanzees, the Dikika

child s small endocranial volume suggests a prolonged period of brain development relative to chimpanzees.

Growth and maturation rates are associated with infant care strategies in primates, suggesting that the prolonged period of brain growth in A. afarensis may have been associated with a long dependence on caregivers. Initially, slow brain growth may have evolved as a way to distribute the energy needs of dependent offspring over many years in environments where food is not abundant. Protracted brain growth in A. afarensis provided a basis for the later development of the brain and social behaviour in hominins and was probably crucial for the development of an extended period of childhood learning.

Fig. 117: Age at death of the Dikika infant based on scans from ID19. Matching of the permanent right lower first molar and left upper canine for age at death determination using synchrotron virtual dental histology.

Fig. 116: Brain imprints in fossil skulls of the species Australopithecus afarensis (famous for Lucy, and the

Dikika child from Ethiopia pictured here in frontal and lateral view) suggest that Australopithecus afarensis

had an ape-like brain and prolonged brain growth.