The 23rd IPPA Congress
Embedded Files
S12
DRIVERS OF HUMAN EVOLUTION IN ASIA: DIVERSITY AND RESILIENCE
Evolution of Human-Like Helpless Infancy in Homo erectus and Homo floresiensis
Yousuke Kaifu1*, Wataru Yano2, Makoto Hikosaka3, Daisuke Shimizu4, Takeshi Nishimura5, Daisuke
Kubo6, Rusyad Adi Suriyanto7, Jatmiko8, Thomas Sutikna9,10, Naoki Morimoto11, and Iwan Kurniawan12
1The University Museum, The University of Tokyo, Japan; 2Department of Biology, National Defense Medial College, Japan; 3Department of Plastic and Reconstructive Surgery, National Center for Child Health and Development, Japan; 4Department of Physical Therapy, Faculty of Nursing and Rehabilitation, Chubu Gakuin University, Japan; 5Center for the Evolutionary Origins of Human Behavior, Kyoto University, Japan; 6Faculty of Medicine, Hokkaido University, Japan; 7Laboratory of Bioanthropology and Paleoanthropology, and Department of Forensic Medical Science and Medicolegal, Faculty of Medicine, Public Health and Nursing, Gadjah Mada University, Indonesia; 8Pusat Riset Arkeologi Prasejarah dan Sejarah, Badan Riset dan Inovasi Nasional, Indonesia; 9Australian Research Council Centre of Excellence for Australian Biodiversity and Heritage, University of Wollongong, Australia; 10Centre for Archaeological Science, School of Earth, Atmospheric and Life Sciences, University of Wollongong, Australia; 11Laboratory of Physical Anthropology, Graduate School of Science, Kyoto University, Japan; 12Center for Geological Survey, Indonesia; *kaifu@um.u-tokyo.ac.jp
Unlike other catarrhine primates, modern humans deliver a helpless newborn who requires prolonged extensive care. Such helpless infancy is associated with fetus-like, rapid postnatal brain growth, which is essential to produce the large human brain. The evolutionary origin of this unique adaptation is controversial. A key question has been whether it emerged in Homo erectus, whose brain sizes were ~20–40% smaller than Homo sapiens. We here show that a type of asymmetric cranial deformity, called deformational plagiocephaly, can serve as a direct indicator of helpless infancy in the hominin fossil record. Because clinical studies have established that such deformation results primarily from an immature state of cranial bones and neck/body muscles, deformational plagiocephaly (or at least its marked condition) must be unique to humans among extant hominids (or more broadly catarrhine primates). Our metric examination based on 1504 cranial specimens (996 great apes and 508 modern humans) support this working hypothesis. We also have found that some cranial fossils of Indonesian Homo erectus and Homo floresiensis also display such deformities. These support a deep evolutionary origin of hominin helpless infancy and imply both elaborate parental childcare and cooperative social behaviours that could likely have accompanied it.
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