The Spinal Cord in Hominin Evolution

Abstract

Spinal cord dimensions increased in both relative and absolute terms during the course of hominin evolution. Recent discoveries demonstrate the presence of a fully developed human‐sized cervical spinal cord in Australopithecus afarensis at 3.6 million years before present (Ma) and in the cervical and thoracic regions of Homo erectus at 1.8 Ma. The fossil evidence suggests that these hominins possessed a fully human‐like postcranial neurological substrate for precision coordination of the arm and hand, corroborated by corresponding skeletal anatomy of the hand and shoulder, as well as discoveries of penecontemporaneous lithic use and putative throwing manuports in the archaeological record. These new fossils provide insight into the neurobiological underpinnings of sophisticated manual behaviours, and overturn prior thinking on the evolution of the central nervous system in the human lineage, indicating that the evolution of the hominin spinal cord was completed well in advance of advances in brain size.

Key Concepts

  • The brain and spinal cord are both larger in humans than those of the African great apes.
  • New Australopithecus afarensis fossils from Woranso‐Mille, Ethiopia, demonstrate that hominin cervical spinal cord enlargement was completed by at least 3.6 million years ago.
  • Evidence from Homo erectus now shows that hominin thoracic spinal cord enlargement was completed by at least 1.8 million years ago.
  • These new discoveries reveal the neurological capability for fine‐motor coordination of the arm, hand, and thoracic muscles in our smaller brained ancestors.
  • It is now apparent that spinal cord expansion was completed prior to brain size expansion in the human lineage.

Keywords: spinal cord; human evolution; brachial plexus; Australopithecus; Homo erectus

Figure 1. Comparison of representative third cervical and fourth thoracic vertebrae from Dmanisi and KNM‐WT 15000 Homo erectus with Homo sapiens (left) and Pan troglodytes (right). Note the enlarged spinal canal in H. erectus relative to Pan.
Figure 2. Comparison of KSD‐VP‐1/1 Australopithecus afarensis fourth cervical vertebra with H. sapiens and P. troglodytes. Note the ventrolateral shoulders and overall enlargement of the spinal canal in KSD‐VP‐1/1 relative to Pan.
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References

Almecija S and Alba DM (2014) On manual proportions and pad‐to‐pad precision grasping in Australopithecus afarensis. Journal of Human Evolution 73: 88–92.

Brown F, Journal H, Leakey R and Walker A (1985) Early Homo erectus skeleton from west Lake Turkana, Kenya. Nature 316: 788–792.

Campbell EJM (1974) Muscular activity in normal and abnormal ventilation. In: Wyke B (ed) Ventilatory and Phonatory Control Systems, pp. 3–11. Oxford: Oxford University Press.

Clark JD (1955) The stone ball: its associations and use by prehistoric man in Africa. In: Balout L (ed.) II Congrès Panafricain de Préhistoire, Alger. Actes de la IIe session, pp. 403–407. Paris: Arts et Métieres graphiqies.

Dommisse GF (1975) Morphological aspects of the lumbar spine and lumbosacral region. Orthopedic Clinics of North America 6 (1): 163–175.

Draper MH, Ladefoged P and Whitteridge D (1959) Respiratory muscles in speech. Journal of Speech and Hearing Research 2: 16–27.

Elliott HC (1945) Cross‐sectional diameters and areas of the human spinal cord. Anatomical Record 93: 287–293.

Gomez‐Olivencia A, Carretero JM, Arsuaga JL, et al. (2007) Metric and morphological study of the upper cervical spine from the Sima de los Huesos site (Sierra de Atapuerca, Burgos, Spain). Journal of Human Evolution 53: 6–25.

Gray H, Williams PL and Warwick R (1975) Functional Neuroanatomy of Man. Philadelphia: Saunders.

Haile‐Selassie Y, Latimer BM, Alene M, et al. (2010) An early Australopithecus afarensis postcranium from Woranso‐Mille, Ethiopia. Proceedings of the National Academy of Sciences 107: 12121–12126.

Harmand S, Lewis JE, Feibel CS, et al. (2015) 3.3‐million‐year‐old stone tools from Lomekwi 3, West Turkana, Kenya. Nature 521: 310–315.

Hirasaki E, Moore ST, Raphan T and Cohen B (1999) Effects of walking velocity on vertical head and body movements during locomotion. Experimental Brain Research 127: 117–130.

Hixon TJ and Weismer G (1995) Perspectives on the Edinburgh study of speech breathing. Journal of Speech and Hearing Research 38: 42–60.

Hoit JD, Banzett RB, Brown R and Loring SH (1990) Speech breathing in individuals with cervical spinal cord injury. Journal of Speech and Hearing Research 33: 798–807.

Issac B (1987) Throwing and human evolution. African Archaeological Review 5: 3–17.

Johanson DC and Taieb M (1976) Plio‐Pleistocene hominid discoveries in Hadar, Ethiopia. Nature 260: 293–297.

Johanson DC, Lovejoy CO, Kimbel B, et al. (1982) Morphology of the Pliocene partial Hominid skeleton (A.L. 288–1) from the Hadar Formation, Ethiopia. American Journal of Physical Anthropology 57: 432–451.

Kivell TL (2015) Evidence in hand: recent discoveries and the early evolution of human manual manipulation. Philosophical Transactions of the Royal Society of London B 370: pii: 20150105.

Klein TJ and Lewis MA (2012) A physical model of sensorimotor interactions during locomotion. Journal of Neural Engineering 9 (4): 6011.

Ko H‐Y, Park JH, Shin YB and Baek SY (2004) Gross quantitative measurements of spinal cord segments in humans. Spinal Cord 42: 35–40.

Latimer B and Ward C (1993) The thoracic and lumbar vertebrae. In: Walker A and Leakey R (eds) The Nariokotome Homo erectus Skeleton, pp. 266–293, chap. 12. Cambridge: Harvard University Press.

Lovejoy CO, Johanson DC and Coppens Y (1982) Elements of the axial skeleton recovered from the Hadar formation: 1974–1977 collections. American Journal of Physical Anthropology 57: 631–635.

MacLarnon AM (1987) Size Relationships and the Spinal Cord and Associated Skeleton in Primates. London: University of London.

MacLarnon AM (1993) The vertebral canal. In: Walker A and Leakey R (eds) The Nariokotome Homo erectus Skeleton, pp. 359–390, chap. 15. Berlin: Springer‐Verlag.

MacLarnon AM (1995) The distribution of spinal cord tissues and locomotor adaptation in primates. Journal of Human Evolution 29: 463–482.

MacLarnon AM (1996) The evolution of the spinal cord in primates: evidence from the foramen magnum and the vertebral canal. Journal of Human Evolution 30: 121–138.

MacLarnon AM and Hewitt GP (1999) The evolution of human speech: the role of enhanced breathing control. American Journal of Physical Anthropology 109: 341–363.

MacLarnon AM and Hewitt GP (2004) Increased breathing control: another factor in the evolution of human language. Journal of Human Evolution 13: 181–197.

McPherron SP, Alemseged Z, Marean CW, et al. (2010) Evidence for stone‐tool‐assisted consumption of animal tissues before 3.39 million years ago at Dikika, Ethiopia. Nature 466: 857–860.

Melillo SM (2016) The shoulder girdle of KSD‐VP‐1/1. In: Haile‐Selassie Y and Su D (eds) The Postcranial Anatomy of Australopithecus afarensis: New Insights from KSD‐VP‐1/1, pp. 113–142, chap. 6. New York: Springer.

Meyer MR (2005) Functional Biology of the Homo erectus Axial Skeleton from Dmanisi, Georgia. PhD dissertation, University of Pennsylvania, Philadelphia.

Meyer MR and Haeusler M (2015) Spinal cord evolution in early Homo. Journal of Human Evolution 88: 43–53.

Meyer MR (2016a) The cervical vertebrae of KSD‐VP‐1/1. In: Haile‐Selassie Y and Su D (eds) The Postcranial Anatomy of Australopithecus afarensis: New Insights from KSD‐VP‐1/1, pp. 63–112, chap. 5. New York: Springer.

Meyer MR (2016b) New Vertebral Fossils from the KSD‐VP‐1/1 Australopithecus afarensis Skeleton. Paleoanthropology Society Annual Meeting, Atlanta.

Meyer MR and Haile‐Selassie Y (2016) The KSD‐VP‐1/1 Postcranial Skeleton from Woranso Mille, Ethiopia: Brachial Plexus Enlargement and the Capacity for Fine Motor Skills in Australopithecus afarensis. 85th Annual Meeting of the American Association of Physical Anthropologists.

Nicaise C, Frank DM, Hala TJ, et al. (2013) Early phrenic motor neuron loss and transient respiratory abnormalities after unilateral cervical spinal cord contusion. Journal of Neurotrauma 30: 1092–1099.

Plaisant O, Sarrazin JL, Cosnard G, Schill H and Gillot C (1996) The lumbar anterior epidural cavity: the posterior longitudinal ligament, the anterior ligaments of the dura mater and the anterior internal vertebral venous plexus. Acta Anatomica 155: 274–281.

Roach NT, Venkadesan M, Rainbow MJ and Lieberman DE (2013) Elastic energy storage in the shoulder and the evolution of high‐speed throwing in Homo. Nature 498: 483–486.

Robinson JT (1972) Early Hominid Posture and Locomotion. Chicago: University of Chicago Press.

Romanes GJ (1964) Motor pools of the spinal cord. In: Eccles JC and Schade JP (eds) Organization of the Spinal Cord, pp. 93–119. Amsterdam: Elsevier.

Sadler TW and Langman J (2005) Langman's essential medical embryology. Philadelphia: Lippincott Williams & Wilkins.

Sanders WJ (1998) Comparative morphometric study of the australopithecine vertebral series Stw‐H8/H41. Journal of Human Evolution 34: 249–302.

Schultz AH (1930) The skeleton of the trunk and limbs of higher primates. Human Biology 3: 303.

Sherman JL, Nassaux PY and Citrin CM (1990) Measurements of the normal cervical spinal cord on MR imaging. American Journal of Neuroradiology 11: 369–372.

Stout D and Chaminade T (2007) The evolutionary neuroscience of tool making. Neuropsychologia 45: 1091–1100.

Tamplin J, Baker FA, Grocke D, et al. (2013) Effect of singing on respiratory function, voice, and mood after quadriplegia: a randomized controlled trial. Archives of Physical Medicine and Rehabilitation 94: 426–434.

Vekua A, Lordkipanidze D, Rightmire GP, et al. (2002) A new skull of early Homo from Dmanisi, Georgia. Science 297: 85–89.

Xiang Y, Yakushin SB, Kunin M, Raphan T and Cohen B (2008) Head stabilization by vestibulocollic reflexes during quadrupedal locomotion in monkey. Journal of Neurophysiology 100: 763–780.

Zimmer MB, Nantwi K and Goshgarian HG (2007) Effect of spinal cord injury on the respiratory system: basic research and current clinical treatment options. Journal of Spinal Cord Medicine 30: 319–330.

Further Reading

Haile‐Selassie Y, Lovejoy CO, Latimer B, Melillo SM and Meyer MR (2016) Implications of KSD‐VP‐1/1 for early hominin paleobiology and insights into the last common ancestor (LCA). In: Haile‐Selassie Y and Su D (eds) The Postcranial Anatomy of Australopithecus afarensis: New Insights from KSD‐VP‐1/1, pp. 179–187, chap. 9. Dordrecht: Springer.

Issac B (1987) Throwing and human evolution. African Archaeological Review 5: 3–17.

Kivell TL (2015) Evidence in hand: recent discoveries and the early evolution of human manual manipulation. Philosophical Transactions of the Royal Society of London B 370: pii: 20150105.

Meyer MR and Haeusler M (2015) Spinal cord evolution in early Homo. Journal of Human Evolution 88: 43–53.

Stout D and Chaminade T (2007) The evolutionary neuroscience of tool making. Neuropsychologia 45: 1091–1100.

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Meyer, Marc R(Aug 2016) The Spinal Cord in Hominin Evolution. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0027058]