Table Of ContentAN INTRODUCTION TO
H U M AN
E V O L U T I O N A RY
A N A T O MY
L E S L IE A I E L LO
Department of Anthropology and the Hominid Biology Research Group,
University College London, UK
C H R I S T O P H ER D E AN
Department of Anatomy and Developmental Biology, University College London, UK
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FOREWORD
My initial response to the authors' invitation have all faced, at one time or another, the
to introduce this book was to undertake a problem of describing or comparing a piece
modest comparative study in order to estab of hominid anatomy, and ending up using
lish how a 'good' foreword should be con an unhappy amalgam of 'Martin', 'Raven',
structed. Regrettably, the results provided no and others, in order to find adequate words
clear guidance, but there was a definite and measurements to describe what, in detail,
pattern to the variation. Some forewords is a novel structure. While it must always be
explicitly offered the equivalent of 'covering the case that human and other higher primate
fire' to shield a text that was innovative, anatomy will provide the starting point for
controversial, or sometimes both. Others attempts to understand hominid form and
took the form of an intellectual 'warranty', function, researchers are increasingly seeking
implicitly underwriting, or vouching for, the to interpret form in terms of structural and
veracity and relevance of what followed. A functional 'rules' which have a much wider
third category comprised the 'testimonial' application. Hominids will need to be
variety in which a respected figure attests to described and explained on their own terms,
the worthiness of the text, much as a purveyor and this book introduces and explains the
of quack medicines reels off the names of language that should be used for those tasks.
social notables who are prepared to testify On the face of it, 1990, the beginning of
to the success of a hair restorer, or tonic. a new decade, seems to be a singularly
Fortunately, this book has no need for any inopportune time to be offering a classical
of these three varieties of foreword, nor, for text of form and structure. Surely the language
that matter, does it require any other form of splicing and cloning is more relevant to
of support or validation. the run up to the twenty first century, than
The authors were perspicacious enough to the details of hypoconulids, frontal trigones
have identified the need for a textbook which, and third trochanters? We must all acknowl
for student and researcher alike, would edge and accommodate to the increasing role
present the anatomical background to the that molecular biology has played, and will
study of human evolution. Fossil hominids play, in the task of exploring the relationships
and hominoids are unique, and there has between taxa. However, recent developments
developed an increasing realisation that in phylogenetic analytical techniques, and
'Whiggish' methods of analogy are outmoded increasingly sophisticated programmes of
as the basis for research strategies aimed at functional analysis, make it more important
solving the puzzle of human evolution. We than ever that the developmental and com-
Vll
FOREWORD
parative contexts of hominid anatomy are this book, the care taken to plan the text-
well understood. This book is designed to figures is evident, and the artist deserves
facilitate such research programmes. particular praise for her efforts.
The complementary interests of Leslie We must be grateful that Leslie Aiello and
Aiello and Christopher Dean have enabled Christopher Dean were equipped with the
them to face, and rise to, the challenge of vision to conceive of, and the industry to
providing a balanced and systematic account prepare, such a useful text as An Introduction
of a wide range of anatomy relevant to to Human Evolutionary Anatomy. Their
both functional analysis and phylogenetic reward will be a book that is a worthy
reconstruction. The authors have chosen an companion to Napier and Napier's A Hand
unashamedly analytical presentation, being book of Living Primates. My prediction is
careful to provide the 'chapter and verse' that it will have a long and useful life, and
behind each proposition. Particular care has that future generations will wonder how their
been taken to commission 'intelligent' art predecessors ever managed without it.
work. All too often diagrams are an after
thought to the text, so that they often make Bernard Wood
no more than a marginal contribution. In The University of Liverpool
Vlll
ACKNOWLEDGEMENTS
We must first acknowledge and thank our every chapter of this book and we thank him
students who initially recognized the need for undertaking the task of reading the
for this book. They convinced us that we manuscript as well as for his friendship,
should attempt to clarify the sometimes rather support and constant encouragement in this
esoteric comparative anatomy that makes up project. We also owe special thanks to Clark
at least part of the literature in human Howell, Rob Foley, David Pilbeam and Bob
evolution. As a result, we have done our best Martin who each offered support for this
to bring together, in a functional and a book at the very beginning.
comparative context, the comparative ana Over the past three years a great number
tomy of living humans and apes with that of of our friends and colleagues have read parts
the early fossil hominids. We have tried to of the manuscript and have made constructive
do this in plain English and in a format that suggestions. Without their help our task
will provide a well illustrated and easy-to- would have been much more difficult and we
use companion for students, teachers and owe the following a great debt of gratitude:
researchers in human evolution, who have Fred Anapol, Peter Andrews, Baruch Arens
until now had no single source to draw on burg, Tim Arnett, Jan Austin, David Beynon,
at this level. We would also like to think that Tim Bromage, Andrew Chamberlain, Dave
there is much within this book that will be Daegling, Michael Day, Bill Hylander, Sheila
interesting and useful for others in archae Jones, Bill Jungers, Gail Kennedy, Bill
ology, dentistry, medicine, speech science Kimbel, Anne MacLarnon, Theya Molleson,
and zoology, who pursue issues that touch Monte Montemurro, Tom Naiman, John
on aspects of hominoid anatomy and human Pegington, Yoel Rak, Pat Smith, Chris Str
evolution. inger, Gen Suwa, and Russ Tuttle.
In attempting this task we must first thank While writing this book many of our
our own teachers, Bernard Campbell, Michael students in the Department of Anatomy and
Day, Geoffrey Harrison, and Bernard Wood, Developmental Biology and in the Depart
who introduced us to human evolution and ment of Anthropology at University College
successfully passed on to us some of their London have helped by clarifying (and some
own knowledge of and enthusiasm for the times by discovering) important information
subject. We are especially grateful to Bernard that is not immediately obvious in the
Wood who read and commented on the entire literature, and also by carrying out original
manuscript. He is one of the few people in research in areas that had been overlooked by
the field today whose knowledge extends into the field. Here we would like to acknowledge
IX
A CKNO WLEDGEMENTS
Heather Baldwin, Stephen Baycroft, Sean speaks for itself and has brought the whole
Blaney, Rogan Corbridge, Helen Liverside, subject to life. We are also grateful to Mike
Mark Thompson, and Jason Spenser. We Gilbert, Jane Pendjiky, and Chris Sims for
would also like to thank the staff of our own their help with the photographic work and
departments for their encouraging support to Joy Pollard for her help with the photo
and also the staff and students of the Depart graphs of the postcrania. Special thanks also
ment of Anthropology, Yale University, who go to Robert Kruszynski for providing helpful
offered their hospitality to one of us (LA) access to the hominid and cast collection of
during the 1987-1988 academic year when the British Museum (Natural History) as well
the majority of the chapters on the postcranial as to Molly Badham and Twycross Zoo for
anatomy were written. Especial thanks go to supply of the nonhuman primate specimens
Mark Birchette, Jon Marks, Alison Richard, upon which much of the original research on
and Marion Swartz and also to Laura Bishop, ape soft tissue anatomy was conducted.
Nora Giles, Danny Povinelli, Patricia Prince- We would also like to offer sincere thanks
house, Todd Preuss, Melissa Remis, Jeff to Andrew Richford and Carol Parr and to
Rogers, David Sprague, Eleanor Sterling, and the rest of the editorial staff at Academic
Andrew Young. Press for their unfailing support, enthusiasm
We are also very grateful to the following and hard work in bringing this project to
who have allowed us to reproduce photo completion. We also are indebted to Anne
graphs of fossils, figures, radiographs and Ginger who gave up her Christmas holiday
micrographs of bone and teeth in this book: to help correct the proofs and to Richard
Peter Abrahams, David Beynon, Alan Boyde, Bruce for support throughout the project.
Michael Day, Sheila Jones, Bill Jungers, Gail Not least we are grateful to our families and
Kennedy, OJ Lewis, Lawrence Martin, Yoel friends without whose help and support we
Rak, Mike Rose, Holly Smith, Jack Stern, would not have been able to complete this
Chris Stringer, Randy Susman, Russ Tuttle, project.
and Alan Walker. We are indebted to Joanna
Cameron for her tireless skill in producing Leslie Aiello
the illustrations for this book. Her talent Christopher Dean
χ
CHAPTER ONE
AN INTRODUCTION TO
CLASSIFICATION,
PHYLOGENETIC
RECONSTRUCTION AND
THE FOSSIL RECORD
Anatomy is the science of the structure of vides the basis for the reconstruction of the
animals, and comparative anatomy provides path taken by a particular animal or group
the main basis upon which our knowledge of animals during evolutionary history. Such
of the course of human evolution is based. an exercise in evolutionary inference is known
In order to interpret the fossils, to determine as phylogenetic reconstruction, which liter
what hominid fossils were like in life, it is ally means the reconstruction of the gener
necessary to compare the structure of their ation or development of a tribe (phylon (Gk)
fossil bones and teeth to those of humans, = a tribe; genesis (Gk) = generation). The
apes and other primates. This can help us to utility of comparative anatomy does not stop
determine not only that they were on the here, however. It also forms the basis of our
human line, but also details about their system of classification, or the naming and
function, how they moved and what they categorizing of fossil animals. Because it is
ate. Only by such analogy with modern impossible to apply the test of breeding
humans and non-human primates can we compatibility to fossils, fossil species are
have confidence in our conclusions about the defined in the first instance on the basis of
nature of our evolutionary ancestors. their anatomy. This exercise is normally
Comparative anatomy also has further uses guided by the rule that fossils can be included
to the palaeoanthropologist. By understand in a single species if they vary no more from
ing the ways in which bones and teeth grow each other than do the members of an average
and develop in humans and other primates it modern species.
is becoming possible to determine the speed A good working understanding of com
and the course of their individual growth and parative anatomy is therefore essential for the
development to adulthood, their ontogeny palaeoanthropologist, and to this end the
(ontos (Gk) = really; gennan (Gk) = to following chapters are primarily concerned
produce). Comparative anatomy also pro with an introduction to and interpretation of
1
AN INTRODUCTION TO HUMAN EVOLUTIONARY ANATOMY
the anatomy of humans, of apes and of the Basic Expanded
major fossils on the human evolutionary line. Hierarchy Hierarchy
These chapters are oriented primarily towards
the first two uses of comparative anatomy,
Kingdom Kingdom
towards the interpretation of structure and
Phylum Phylum
function and towards the interpretation of
Subphylum
the ontogeny, or growth and development Superclass
of the hominids. However, before embarking Class Class
Subclass
on this excursion into comparative anatomy
Infraclass
a few more detailed comments about the uses Cohort
of comparative anatomy in phylogenetic Superorder
Order Order
reconstruction and in classification will be
Suborder
helpful to students who are working with, Infraorder
or anticipating working with, fossil material. Superfamily
Family Family
Subfamily
Tribe
Subtribe
Classification and phylogenetic
Genus Genus
reconstruction Subgenus
Species Species
Biological classification makes no claim about Subspecies
evolution or evolutionary relationships. It
simply involves the ordering of organisms
FIGURE 11 The Linnean Hierarchy.
into groups on the basis of their anatomical
similarities and differences. The system that
is currently in use is known as the Linnean
Hierarchy and dates in its (near) present form
to 1758 and the 10th edition of Linnaeus'
Systema Naturae. The Linnean Hierarchy is = listing of names), the application of names
a pyramidal structure where each higher to the taxa in the hierarchy, is strictly
category includes a nest, or set, of one or governed by the International Code of
more lower, or subordinate, categories. At Zoological Nomenclature. This code is based
the minimum there are seven levels to this on the concept of name-bearing types, which
hierarchy but in practice modern applications are particular specimens or taxa that provide
may include 20 or more separate hierarchical an objective standard of reference against
levels (Fig. 1.1). which other specimens or taxa must be
A taxon (taxis (Gk) = arrangement) is a compared before they are included in the
group of organisms at any level of the rank of interest. For example, each family
hierarchy (such as a genus or a species or or subfamily has a type genus, each genus
a family) and taxonomy (taxis (Gk) = a type species and each species a type
arrangement; nomous (Gk) = law) is literally specimen. The code stipulates that a family
the theoretical study of the laws, procedures or subfamily name is formed by adding to
and principles of the arrangement of organ the stem of the name of the type genus the
isms. We will shortly show that there is latinized suffix '-idae' for a family name and
considerable difference of opinion over the '-inae' for a subfamily name. Moreover, it
manner in which taxa (= plural of taxon) recommends that the suffix '-oidea' be added
should be grouped in the hierarchical system. to the stem for the name of a superfamily
However, there is no possibility for difference and '-ini' for the name of a tribe. For
of opinion over how various taxa are defined example, in the classification of the human
and named. Nomenclature (nomenclatos (L) species, the genus Homo gives its name
2
CLASSIFICATION, PHYLOGENETIC RECONSTRUCTION AND THE FOSSIL RECORD
to the tribe Hominini to the subfamily bearing type(s) for that species. These terms
Homininae to the family Hominidae and to refer to particular categories of name-bearing
the superfamily Hominoidea (see Figs 1.6 type that are important in the definition of
and 1.7). a new species. The holotype is the single
The code also specifies that all species (and specimen designated as the name-bearing type
only species) should be referred to by two of a species or subspecies when it was
names, their genus name and their species established. Each specimen of a type series
name. Such a double name is known as a other than the holotype is known as a
binomen and is the reason why this naming paratype. A type series consists of all the
system is known as the system of Binominal specimens eligible to be name-bearing types
Nomenclature. The genus name always included in the original description of a new
begins with an upper-case letter and the species.
species name with a lower-case one as, for The International Code of Zoological
example, Homo sapiens, the binomen for Nomenclature lays out specific rules for both
modern humans. Frequently with fossil the establishment and the naming of taxa,
material it may not be possible to assign a but other areas of classification engender
particular specimen to a particular species, potential controversy and deserve further
but it may be possible to assign it to the next discussion. These areas are: (1) the definition
highest taxonomic level, the genus. In this of and recognition of species; (2) the grouping
case the binomen for that specimen would of taxa into an hierarchical system; and (3)
be, for example, Homo sp. indet. which the assignment of taxa to their proper levels
identifies the particular specimen as a member in the Linnean Hierarchy.
of the genus Homo but of an indeterminate
species. The definition and recognition of
species
Sometimes the term 'cf.' (= confer) may
also be included in a binomen as, for example, Species are the lowest level in the Linnean
Homo cf. erectus. This indicates that there is Flierarchy. However, this definition of spec
some doubt about the formal referral of the ies is not of much use to the practical
particular specimen to the species erectus. A palaeontologist or palaeoanthropologist who
species name might also be qualified as, for is trying to define species or to assign
example, Homo habilis s.s. (= sensu stricto) particular fossil specimens to one or another
or Homo habilis s.l (= sensu lato). The use species. A number of other definitions of the
of these terms is not governed by the species are more useful for this purpose.
International Code. However sensu stricto is Perhaps the most common definition of
generally used in the sense of the type of the species is the biospecies definition of Mayr
species, referring specifically to those fossil (1940: 254). Here biospecies are defined as
specimens that are formally included in the groups of actually or potentially interbreeding
type series of the taxon (see below). Likewise, natural populations, which are reproductively
sensu lato refers to the broader (and perhaps isolated from other such species. This defi
more variable) group of specimens that might nition is directly applicable only to contem
have been referred to the species subsequent poraneous living organisms and has been
to its formal establishment. Such a group of criticized by Simpson (1961) for not explicitly
referred specimens is known as the hypodigm. addressing the evolutionary duration, or
time-depth, of a species. Consequently, he
As a last general word about the Inter
proposes a definition for evolutionary species
national Code of Zoological Nomenclature
in which 'an evolutionary species is a lineage
it is also common to see various fossil
(an ancestral-descendant sequence of
specimens referred to as holotypes or para-
populations) evolving separately from others
types. A new species must have a designated
and with its own unitary evolutionary role
specimen or series of specimens as the name-
3
AN INTRODUCTION TO HUMAN EVOLUTIONARY ANATOMY
and tendencies' (Simpson, 1961: 153). This with morphospecies, which are species
definition emphasizes reproductive conti defined on the basis of morphological, or
nuity through time and is similar to a more anatomical, similarity, regardless of other
modern definition proposed by Wiley (1978: considerations (Simpson, 1961). It must be
18) which defines a species as . . a single clearly recognized that any inferences about
lineage of ancestral descendant populations breeding compatibility are just hypotheses
of organisms which maintains its identity based on anatomical similarity and that there
from other such lineages and which has its is always considerable room for doubt about
own evolutionary tendencies and historical the boundaries of fossil species.
fate'. Other definitions of species that are appli
These species definitions have one very cable to fossil species are palaeospecies and
basic problem when applied to extinct organ chronospecies. These terms both refer to
isms. Any inference about breeding contin temporally successive species in a single
uity in the fossil record must be based on lineage (Simpson, 1961). The problem here
continuity of anatomical characters in the is to identify where in a continuous lineage
fossils, assuming an equivalence between one species ends and the next begins. For
anatomical similarity and breeding compati example, in human evolution, if one posits a
bility. Indeed, Simpson has suggested that linear relationship between, say, Homo
if the ranges of population variation in erectus and Homo sapiens, where does the
anatomical features of two or more samples former end and the latter begin? Simpson
overlap for all observable characters it is (1961: 165) suggests that 'Successive species
likely that the samples come from one should be so defined as to make the morpho
interbreeding population, or biospecies. Con logical difference between them at least
versely, if the ranges of variation do not as great as sequential differences among
overlap it is likely that the samples come from contemporaneous species of the same group
two distinct biospecies. However, things are or closely allied groups'. There are some
never as clear cut as this in the fossil record, taxonomists, particularly those adhering to
where there are frequently ambiguous ranges the school of phylogenetic systematics (see
of overlap between fossil samples. Moreover, below), who believe that there is no cause to
there is no evidence that there is any hard divide continuous, non-branching, lineages
and fast relationship between speciation and into palaeospecies or chronospecies. In other
anatomical change (Vrba, 1980; Tattersall, words, these workers argue that if there is a
1986; Turner and Chamberlain, 1989). In continuous lineage from, say, Homo habilis
human palaeontology this issue becomes very to H. sapiens, that does not give rise to side
important in relation to the later-occurring branches, this lineage should be included in
fossils such as Neanderthals. The question one evolutionary species (i.e. H. sapiens)
at issue here is whether the anatomical (Eldredge and Cracraft, 1980; Bonde, 1981).
differences between Neanderthals and mod In this case H. sapiens would be the species
ern humans justify species distinction between name with historical priority.
these hominids, e.g. Homo neanderthalensis
and Homo sapiens, and if so whether this The grouping of taxa into an
species distinction also implies breeding iso hierarchical system
lation between these species with the obvious The grouping of taxa into an hierarchical
implication that, by definition, Neanderthals system involves the formation of nested sets,
could not have contributed to the modern where say a group of similar species is placed
human gene pool. in one set and a number of such sets are
When it comes down to it, palaeontologists grouped together into a higher set and so on
are, in the first instance, confined to working up the hierarchy. Such hierarchical grouping
4
