Human Evolution: an Illustrated Introduction
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FIFTH EDITION HUMAN EVOLUTION: AN ILLUSTRATED INTRODUCTION Roger Lewin © 1984, 1989, 1993, 1999, 2005 by Blackwell Publishing Ltd 350 Main Street, Malden, MA 02148-5020, USA 108 Cowley Road, Oxford OX4 1JF, UK 550 Swanston Street, Carlton, Victoria 3053, Australia The right of Roger Lewin to be identified as the Author of this Work has been asserted in accordance with the UK Copyright, Designs, and Patents Act 1988. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, except as permitted by the UK Copyright, Designs, and Patents Act 1988, without the prior permission of the publisher. First edition published 1984 by Blackwell Publishing Ltd Second edition published 1989 Third edition published 1993 Fourth edition published 1999 Fifth edition published 2005 Library of Congress Cataloging-in-Publication Data Lewin, Roger. Human evolution : an illustrated introduction / Roger Lewin.a5th ed. p. cm. Includes bibliographical references and index. ISBN 1-4051-0378-7 (pbk. : alk. paper) 1. Human evolution. I. Title. GN281.L49 2005 599.93’8adc22 2003024250 A catalogue record for this title is available from the British Library. 1 Set in 9/11 /2pt Meridien by Graphicraft Limited, Hong Kong Printed and bound in the United Kingdom by William Clowes Ltd, Beccles, Suffolk The publisher’s policy is to use permanent paper from mills that operate a sustainable forestry policy, and which has been manufactured from pulp processed using acid-free and elementary chlorine-free practices. Furthermore, the publisher ensures that the text paper and cover board used have met acceptable environmental accreditation standards. For further information on Blackwell Publishing, visit our website: http://www.blackwellpublishing.com THE EVOLUTION 32 OF LANGUAGE Language is a unique characteristic of Homo sapiens. Questions of complex mental functions, however, language capabilities when and why spoken language evolved are central to understanding cannot be pinpointed precisely to particular centers. Tradi- our species. Evidence from fossils and archeology address the “when?” tionally, Broca’s area, visible as a small bulge on the left side questionaearly and gradually or late and rapidabut they give of the brain toward the front, has been associated with lan- conflicting conclusions. Why language evolved is equally perplexing. guage, particularly with the production of sound. A second The “obvious” answerafor better communicationawas long favored, center, Wernicke’s area, located somewhat behind Broca’s but more recent ideas focus on the need to construct a better cognitive area, is involved in the perception of sound. (See figure 32.1.) reality. Recent PET scan studies, however, have shown that this con- cept oversimplifies the situation. Many aspects of language One great frustration for anthropologists is that, by its nature, afor instance, the lexicon, or vocabulary with which we language is virtually invisible in the archeological record. workadefy precise localization. Clues must therefore be sought from indirect sources: in Consequently, paleoneurologists can obtain few definite stone tools, among indications of social and economic signs of language capacities from fossil endocasts. Signs of organization, in the content and context of paintings and Broca’s area have been found in Homo rudolfensis and later other forms of artistic expression, and in the fossil remains species of Homo, but not in australopithecines. For this reason, themselves. paleoneurologist Dean Falk believes that language capacity One general question about the evolution of human was already to some degree developed at the beginning of the language relates to the dynamics of its emergence. Was it a Homo lineage. She disagrees with Ralph Holloway, however, slow, gradual process, beginning early in hominin history who argues that language capacity began to develop earlier, and becoming fully modern only recently? Or was it a rapid among australopithecine species. His conclusion is based on process, beginning recently in hominin history? This unit the humanlike brain reorganization he detects in australo- will examine several lines of evidence, taken from fossils and pithecines. In contrast, Falk sees no reorganization in the aspects of behavior identified in the archeological record. human direction until Homo evolves (see unit 31). If the fossil brains provide only tantalizing hints of verbal skills in our ancestors, what can we learn from the voice- Fossil evidence producing apparatus? A number of researchers have pursued this question in recent yearsain particular, Edmund Crelin, In recent years, researchers have pursued several kinds of Philip Lieberman, and Jeffrey Laitman. The human vocal evidence from fossil hominins. First, information is gleaned tract is unique in the animal world. In mammals, the position from endocasts, those crude maps of the surface features of of the larynx in the neck assumes one of two basic patterns the brain. Second, indications of the structure of the voice- (see figure 32.2). One location is high up, which allows the producing apparatus in the neck (the larynx and pharynx) animal simultaneously to swallow (food or liquid) and provide clues as to language ability, as do also the size of the breathe. The second pattern places the larynx low in the hole in the cranium through which the nerve to the tongue neck, requiring temporary closing of the air passage during passes, and the degree of innervation to the diaphragm, as swallowing; otherwise solids or liquids will block it and cause reflected in the size of the spinal canal. choking. Adult humans have the second pattern, while all The major neural machinery for language functions is other mammals, and infant humans, possess the first. The located in the left hemisphere in the great majority of modern low position of the larynx greatly enlarges the space above it, humans, even in most left-handed people. As with many which allows the sounds emitted from it to be modified to a 32: The Evolution of Language 223 Broca’s area Face area Arcuate fasciculus Angular gyrus Figure 32.1 Language centers: Wernicke’s area, which appears to be responsible for content and comprehension of speech, is connected by a nerve bundle called the arcuate fasciculus to Broca’s area, which influences the areas of the brain that control the muscles of the lips, jaw, tongue, soft palate, and vocal cords during speech. These language centers are usually located in the left cerebral hemisphere, even in many left-handers. Sylvian fissure Wernicke’s area Visual cortex great degree. Nonhuman mammals are limited to modifying The tongue plays a major role in producing articulate laryngeal sounds by altering the shape of the oral cavity and speech. In modern humans the hypoglossal nerve is much the lips. Human newborns maintain the basic mammalian larger than in other nonhuman primates. Researchers at pattern until about 1.5 to 2 years; the larynx then begins to Duke University have measured the size of the hole through migrate lower in the neck, achieving the adult configuration which this nerve runs in fossil humans. They found that at approximately age 14 years. by 400,000 years ago, the nerve was apparently already Laitman and his colleagues discovered that the position of enlarged to modern standards. They infer that this indicates the larynx is reflected in the shape of the bottom of the skull, at least the ability to speak was present early on. This is, how- the basicranium. In adult humans, this structure is arched; ever, controversial. in other mammals, and in human infants, it is much flatter. Lastly, Ann McLarnon, of the Roehampton Institute, By looking at this feature in the fossil record, it should there- London, notes that the cross-sectional area of the spinal cord fore be possible to discern something about the verbal skills in humans in the thorax region is relatively large. This is, she of extinct hominin species. What does the fossil record says, related to the need for fine control of breathing, via the indicate? diaphragm, which is required for speech. It is much smaller “In sum,” says Laitman, “we find that the australopith- in Homo ergaster, as seen in the Turkana boy skeleton, 1.6 mil- ecines probably had vocal tracts much like those of living lion years ago. By 400,000 years ago, the spinal cord was monkeys or apes. The high position of their larynges already of modern proportions, which, like the hypoglossal would have made it impossible for them to produce some canal data, may indicate a capacity for speech early on. of the universal vowel sounds found in human speech.” Unfortunately, the fossil record for Homo rudolfensis/habilis is poor as far as indications of the basicranium are concerned. The question of Neanderthals Laitman and his colleagues have found that, in its putative evolutionary successor, Homo ergaster, “the larynx ...may A continuing controversy concerns Neanderthals’ language have begun to descend into the neck, increasing the area abilities. Because they appeared 150,000 years after the fully available to modify laryngeal sounds.” The position of the arched basicranium evolved in archaic sapiens, implying fully larynx appears to be equivalent to that found in an 8-year- developed speech potential in that species, Neanderthals old human. Only with the origin of archaic Homo sapiens, might be expected to be similarly developed. However, basi- some 300,000 years ago, does the fully modern pattern cranial flexion is less than that observed in earlier archaic appear, indicating at least the mechanical potential for the sapiens. It looks as if the direction of evolution had been full range of sounds produced by people today. reversed, depriving Neanderthals of fully articulate speech. 224 Part Eight: The Human Milieu colleagues claim this feature as proof that Neanderthals’ lan- guage capacity resembled that of modern humans.