João Luiz Pinheiro-Franco, Alexander R. Vaccaro, Edward C. Benzel and H. Michael Mayer (eds.)Advanced Concepts in Lumbar Degenerative Disk Disease10.1007/978-3-662-47756-4_1

1. We’ve Been Standing Up for 10 Million Years

Yves Coppens^{1, 2}

(1)

Anthropological Biology – Natural History Museum, Paris, France

(2)

Department of Prehistory and Paleoanthropology, Collège de France, 3 rue d’Ulm, 75231 Paris, France

Yves Coppens

Email: yves.coppens@college-de-france.fr

Keywords

BipedPrimatesEvolutionVertebral columnPelvisLimbs

Editor’s Note

Professor Yves Coppens, along with Donald Johanson and Maurice Taïeb, discovered the now famous “Lucy,” at that time, the oldest bipedal hominid skeleton. The name Lucy was given as reference to the Beatles song, “Lucy in the sky with diamonds,” which was popular at the time of their excavations and research. Prof. Coppens was the Chairman of Anthropological Biology in the Natural History Museum (Paris, France, 1969-1983). For 22 years (1983–2005), he served as Chair of Paleoanthropology and Prehistory at the prestigious Collège de France. He is also member of the “Académie des Sciences de l’Institut de France” (since 1983) and member of the National Academy of Medicine (France) since 1991. From 2005, Professor Coppens serves as Emeritus Professor of Paleoanthropology and Prehistory in the Collège de France. The Collège de France was founded in 1530. Its alumni include renowned scientists such as André-Marie Ampère (1824–1836) and Charles-Édward Brown-Séquard (1878–1894), among others. He has discovered tons of fossils of vertebrates and signed or cosigned six new Hominidae. He was nominated Grand Officier de la Légion D’Honneur of France. His name was given to an asteroid (172850 Coppens).

1.1 Introduction

Editor’s Note

In this chapter, Professor Yves Coppens provides an enlightening perspective regarding a field of science that he pioneered. His account, in conversation form, is unique from historical and scientific perspectives.

Dr. João Luiz Pinheiro-Franco has invited me to contribute to this important work on advanced concepts of degenerative lumbar disk disease. As this subject is undoubtedly beyond my field of expertise, he proposed that I elaborate on the developmental factors involved during the human transition from locomoting in quadruped position to the biped upright standing position, which comfortably fits within my academic considerations.

Thusly framed, I have decided to address the history of our human-primate “kinship,” that period when Homininae separated themselves from the Paninae, probably for environmental reasons, somewhere in tropical Africa, 10 million years ago.

Human beings are, obviously, living beings and as such have their place in a taxonomy of their presumed natural relationships: a chronologically ascending and integrative classification, we are all at once a eukaryote, metazoon, chordate, vertebrate, gnathostomata, sarcopterygian, tetrapod, amniote, synapsid, mammal, and primate. And among primates the taxonomy continues: haplorrhine, simiiform, catarrhinian, hominoid, and hominid. At present, in most scientific classifications, Hominidae include Paninae, which are in common terms the pre-chimpanzees and chimpanzees, and equally include the Homininae, which are the prehumans and humans of today. This leads to the assumption that Paninae and Homininae share a common ancestry.

As it is known that all primates have tropical origin and Paninae stem from African origin, there is the significant probability that this common ancestry and at least their first descendants were tropical and African.

And, in fact, it is only tropical Africa that provided the necessary conditions.

Furthermore, analyses of the great morphological, anatomical, physiological, genetic, molecular, and ethological distances between our “cousins” Paninae and ourselves have allowed us to calculate our last common ancestry to have happened in the upper Miocene, around 10 million years ago, the birth date of our taxonomic subfamily. The location: tropical Africa.

Today, there are three candidates with such an origin and age for this ancestry: Chororapithecus abyssinicus, from Ethiopia, 10.7 to 10.1 million years ago; Nakalipithecus nakayamai, from Kenya, 9.88 to 9.89 million years ago; and Samburupithecus kiptalami, also from Kenya, 9.6 million years ago.

Fossils of these candidates provide an idea of our common ancestor’s appearance, but not clear enough to place them before or after the divergence of Paninae/Homininae, raising the dilemma if they were already Paninae (pre-chimpanzee) or Homininae (prehuman) or existing side by side. What is known is that the location was unequivocably a tropical and forestal biotope and that it was at this time that the separation occurred for environmental reasons. This was the departure point for our evolution as a Homininae, our exclusive developmental path.

Over the course of 10 million years, this path has been recorded by genus and species, primarily prehumans from 10 to 1 million years ago and then humans, from 3 million years ago until today and into the future. This trajectory, therefore, implies that the last prehumans were contemporaries of the first humans.

The prehumans are numerous and differentiate widely into 7 genera and 14 species, discovered in South Africa, Malawi, Tanzania, Kenya, Ethiopia, and Chad, and all share tropical origins that are solely African. These specimens also all possessed a static, permanent upright position with a biped and arboreal locomotion initially, then transitioning to be exclusively bipedal. These prehumans also demonstrate a brain in mild expansion and facial feature undergoing a mild reduction with teeth at times under reduction and at other periods under expansion.

1.2 How Did We Become Upright?

The acquisition of an upright posture – the underlying contingency which made it possible for early humans to extend the trunk, pelvis, thigh, and legs – combined with the resulting bipedal locomotion, represents the key transformation point in the history of Homininae, one that gradually and mechanically induced other transformations, in particular changes in the hands and brain, which facilitated consecutively the emergence of tools and consciousness, culture, and society.

In successive order, from an anatomic and as functional as possible perspective, I shall lay out the underlying factors concerning the acquisition of an upright posture in a static condition and the ability to walk upon the hind feet. The following considerations are based upon observations gleaned from different parts of the skeleton of the Australopithecus afarensis species.

Observations for body size and body displacement movements were made from a fragmentary skeleton excavated from a field in Ethiopia, AL288,¹ a separate group of bones related to the same species from the same excavation field and 34 footprints from a field in Tanzania; indeed AL288 is the most complete archeological sample set known concerning erect posture acquisition and hind feet locomotion.

1.2.1 Vertebral Column

There are ten artifacts to describe the vertebral column, all from skeleton AL288: seven thoracic vertebrae, two lumbar vertebrae, and one sacrum.

The seven thoracic vertebrae – T2, T6, T7, T8, T10, T11, and T12 – are very similar to their human homologues. On initial observation, they differ only for two main features, moreover without any relationship between them: Australopithecus afarensis (AL288) vertebrae are significantly smaller in all linear dimensions. However, there is one exception: the sagittal diameter is proportionally very large as it is artificially increased due to a bony arch on the ventral surface of vertebral bodies.

The two lumbar vertebrae – L3 and L4 – are also small in size. Their morphology and the orientation of their different parts make one surmise that the thoracic kyphosis had extended until them. Therefore, it had been more akin to a thoracolumbar kyphosis with a large radius curvature.

Finally, the sacrum, formed by its five fused parts, appears strikingly human, albeit obviously smaller in measurement and proportion. Besides being shallow, it is proportionately extended at its frontal dimension.

Although extremely fragmentary as evidence, this spinal column clearly represents an upright and erect being. Cervical lordosis was highly likely, while thoracic kyphosis was clearly undeniable, appearing only slightly more stretched downward into the lumbar region than ours today. It is appropriate to consider the human variability in this matter: the sagittal angle of its curvature can be estimated to be between 30° and 40°. Lumbosacral lordosis is also present but, however, clearly reduced due to the thoracolumbar stretch. In addition, lordosis is slight, with a curvature of between 40° and 55°. Furthermore, it is quite probable that the spinal cord had had a lower cervical dilation and lower lumbar component (transversal diameter of T2 triangular and large; sagittotransversal index of the L4 vertebral hole quite high).

1.2.2 Pelvis

Half of the pelvis of the AL288 skeleton is very well preserved. The proportions of this pelvis are human-like; however, its anatomy differs in a certain number of particularly interesting features and in their functional consequences, which we shall touch upon briefly.

Firstly, the iliac bones are oriented in a much more frontal coronal plane than in the human pelvis and are clearly wider than human counterparts. Of the ilium, there is a very slight indentation in the internal iliac fossa and is also very wide. The pelvic cavity is broad and also extended thankfully to the important development of the acetabular diameter and the length of the pubis cranial ramus, with its ventrocaudal inclination. The sacrum is, as previously mentioned, also very wide, though short and slightly curved. The sciatic notch is barely marked, and finally, the coxofemoral joints are seemingly undersized. The length of the caudal segment and the short size of the cranial segment confer the ilium-specific longitudinal proportions: a narrow sacral plane and excessively broad iliac plane attenuating to a slender lower extremity.

Furthermore, the ilium presents an iliac crest almost straight in line between the ventrocranial iliac spine (anterior superior iliac spine) and dorsocranial iliac spine (posterior superior iliac spine). The ventrocranial iliac spine is, indeed, distinctively beak shaped, which at this level results in the superposition of the iliac pillar above the iliac spine.

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