66

Book Review
DENTAL FUNCTIONAL MORPHOLOGY:  HOW 
TEETH WORK.  By Peter W. Lucas.  New York: 
Cambridge University Press, 2004.  372 pages, 7 
chapters, 2 appendices.  $130.00  £75.00

Occasionally in science a novel treatment of a familiar 
subject opens new vistas for exploration and thought. 
This is the case with Dental Functional Morphology by Peter 
W. Lucas.  Part dental anthropology and part physics, 
this book challenges long held paradigms regarding 
the morphology of mammalian teeth.  Viewed from the 
perspective that physical characteristics of food drive 
selection of tooth form, Lucas presents a well thought 
argument revolving around how dental morphology has 
evolved in response to the fracture properties of food.

The adage “if you don’t eat, you die” can be altered 
using Lucas’ view to “if your teeth don’t efficiently 
fracture foods and reduce particle size to that which is 

of the Ainu to the prehistoric Jōmon. Despite his use of 
sophisticated statistics, however, his conclusions savored 
more of preconceived notions than of anything that 
derived from the actual metric data. Without actually 
using odontometric data to test the idea, he debunked 
the old suggestion that there was a “Caucasoid” element 
in the Ainu. As with so many Japanese who want to 
believe that they are descended from the prehistoric 
inhabitants of the archipelago, he tried to push the 
idea that the Jōmon played a role in the ancestry of 
the Japanese which they did to a varying extent.  He 
recognized the fact that most Japanese looked more like 
mainland East Asians than Jōmon-Ainu people, and he 
suggested, in the absence of archaeological support, that 
massive population movements from that mainland 
had been responsible.  His estimate was that more than 
a million people moved from Northeast Asia to Japan 
during the time between 300 BCE and 700 CE, a guess 
that has made more than a few prehistorians uneasy 
and doubtful.

In 1972 he returned to the University of Tokyo as 
Professor of Anthropology in the School of Science 
where he remained until reaching the mandatory 
retirement age of 60.  Starting in 1987, he began what 
was to be a lifelong affiliation with the International 
Research Center for Japanese Studies in Kyoto.  Actually, 
he was one of the major figures involved in setting 
up that Research Center in the first place.  In order to 
make the case to Japanese Prime Minister Nakasone 
for the establishment of that Center, Hanihara traveled 
to America in the spring of 1985 and visited a series 
of Universities to gather expressions of support for 
the project. His efforts were highly successful, and 
this points out one of the most prominent aspects 
of Kazuro Hanihara. He was a marvelous organizer 
and administrator and was a successful chairman of 
a Museum and Department as well as a long series of 
committees. Not only was he admirably well-organized, 
but he exuded a manifestation of graciousness and 
charm that clearly nurtured his success.

Hanihara was probably most known for his proposal 
of a “Dual structure model for the population history of 
the Japanese” first published in 1991. In this, he proposed 
that the prehistoric Jōmon of Japan were derived from 
Southeast Asia which he sometimes referred to as 
“South Asia” although this did not mean the Indian 
sub-continent as that designation has usually implied.  
He suggested that a mixture of Jōmon and Northeast 
Asians gave rise to the Ainu on the one hand and the 
modern Japanese on the other. The difference between 
the two, he proposed, was the result of microevolution 
in situ.  The Jōmon themselves he regarded as qualifying 
as perfectly good “Mongoloids” although this was 
not supported by any kind of metric demonstration. 
The idea that the Ainu represent the continuity of the 
Jōmon with a bit of input from eastern Asia is indeed 

supported by an analysis of common variance, and the 
idea that the Japanese largely represent the morphology 
of eastern Asia tempered by a trace of Jōmon form in 
increasing amounts the farther east one goes in the 
archipelago is also supported by the variance figures.  
However, the role of microevolution in leading to the 
Ainu/Japanese differentiation has no basis, and there 
is no evidence supporting a Southeast Asian locus of 
origin for the Jōmon themselves.

Last but not least, Kazuro Hanihara was enormously 
helpful to visiting scholars who knew little or no 
Japanese. Whether he agreed with the interpretation 
of the results of their work or not, he was unfailingly 
gracious and supportive. He figured out bus and train 
schedules, helped people get to the right stations, he met 
planes, and made hotel reservations, and many more 
much appreciated acts of generosity and assistance. For 
those of us who counted him as a friend, his passing 
leaves a real sense of loss.

C. Loring Brace
Museum of Anthropology
University of Michigan
Ann Arbor, MI, 48109 USA

and

Noriko Seguchi
Department of Anthropology
University of Montana
Missoula, MT, 59812 USA



67

optimal for energy extraction, you die.” As this implies, 
this volume is really an exploration of the mechanics of 
eating from the perspective of how biological material 
is broken down so that as much energy as possible is 
derived from that which is ingested.  Here I will attempt 
to elucidate the main points that Lucas brings forth and 
pique the reader’s interest enough that you will obtain a 
copy; although it is not an easy read, it is certainly thought 
provoking.

The nine sections (seven chapters and two appendices) 
of Dental Functional Morphology can be distilled into two 
groups, namely the core of chapters 4-6 and the periphery.  
The periphery sets up understanding of the core. Chapters 
1-3 present a good background to the anatomy and 
functions of mastication, Chapter 7 provides insight into 
the evolution of mammalian teeth, and the appendices 
present an introduction to the mechanics of fracture in 
solids and the mechanical properties of teeth and foods.

Chapter 1, “How To Get Excited About Teeth,” briefly 
outlines what Lucas is up to and begins one thinking 
of food in terms of how it breaks into smaller particles 
through the forces of mastication.  As stated on page 10 
the aim of the book is to consider “the function of teeth 
in relation to the ingestion, chewing, and swallowing 
of food. It attempts to elucidate the principles that 
underlie the evolution of tooth shape and size and those 
mechanisms by which the dentition can be maintained.”  
The basic point is that teeth need to be viewed as 
anatomical structures in which selection for shape and 
size are a result of the physical properties of the material 
they come in contact with.  Ergo, how teeth deal with two 
aspects of food, the external physical attributes and the 
internal mechanical properties, influences the evolution 
of their structure. Lucas puts this in context for the salient 
aspects of the book in stating, “The chance of hitting a 
food particle with the teeth is enhanced by making the 
tooth bigger, i.e. by changing tooth size.  In contrast, the 
effects of the force that the tooth exerts on that particle 
depend on the contours of its working surface�i.e. on its 
tooth shape” (p. 12). 

Chapters 2 and 3 offer very good review of the anatomy 
and function of the mouth, respectively.  Included in 
Chapter 2 is an in depth overview of the micro- and 
macro-structures of the teeth and masticatory apparatus 
with excellent lateral head and neck drawings.  The 
last lines of the chapter allow an introduction to Lucas’ 
writing style, which is best described as ‘humorously 
quirky’ at times.  This last section deals with the muscles 
of the neck, which he closes thusly, “However, humans 
have an habitual upright bipedal stance in which the 
head is balanced only by continuous active contraction of 
posterior neck muscles such as the longissimi.  Without 
this action, the head falls forward —such as when dozing 
over a book like this.  That is enough about structure” 
(p. 54).   Chapter 3 is a very in depth treatment of the 
mechanisms of mastication.  Jaw movement, food particle 

breakdown, food movement in the mouth, the mechanics 
of swallowing, taste, and the role of saliva are all addressed.  
This chapter begins the process of getting the reader 
thinking about teeth as processors of organic matter and 
is a building block for Lucas’ argument concerning tooth 
size and shape developed in the following chapters.

In most books, appendices are sections that supplement 
the main text and are meant to be perused, or ignored, as 
the reader sees fit.  That is not the case with Appendix 
A.  Before delving into the core of the book, Chapters 4-
6, this is necessary reading.  As a primer on mechanical 
properties and their measurement, Appendix A covers 
material important to understanding  the concepts 
Lucas presents.  He suggests the reader at least “skim” 
this section, I suggest that a careful reading is important 
particularly if your knowledge of the mechanics of 
fracture in solids is limited. Pay particular attention to the 
sections explaining Young’s Modulus (E), a measurement 
of stiffness (elasticity) of materials, and derivations 
for R (toughness) and K

IC
 (fracture toughness) as a 

comprehension of these and other formulae is important 
for following Lucas’ logic trail.

Study of tooth shape (Ch. 4), size (Ch. 5), and wear 
(Ch. 6) is integral to the study of dental anthropology.  
The importance of shape and size, in particular, 
transcends the relatively narrow confines of our specialty 
to encompass the much broader study of the evolution 
of terrestrial life forms.  Since, as we all know, teeth are 
the most often recovered portions of once living beings, 
paleospecies rise and fall based on characteristics relating 
to the size and shape of their teeth.  Therefore, a better 
understanding of possible selective forces impacting 
dental evolution will lead to a better understanding of 
evolution in general.  These three chapters offer readers 
the opportunity to reevaluate what they think they 
know about the evolution of the dentition and gain new 
insight into the microevolutionary forces at play in the 
evolutionary give-and-take between the eaters and that 
which they eat.

It is difficult to explain Lucas’ exploration of the 
properties of food particle fracture and their effect 
on dental form without detailed description and the 
repetition of formulae that would expand this review 
beyond acceptable limits.

The basic premise of Chapter 4, Tooth Shape, is the 
assumption “that the shape of teeth is an evolved response 
for overcoming the toughening mechanisms inside foods 
that frustrate their fracture and that these mechanisms 
lie at the heart of the diversity of dental form” (p. 96). 
This focus on the complex structural properties of food is 
in direct response to the classic, simplistic, view of tooth 
function that lumps teeth into two broad, ill defined, 
categories; shearing and grinding.  By understanding 
the true mechanics of fracture in solids, how cracks are 
initiated and progress, it becomes apparent that “shear” 
and “grinding” are not what is happening at all during 



68

mastication.  Force, applied through the teeth by the 
muscles of mastication, initiates cracks that lead to fracture 
and thence, to reduction in size of solid organic matter.  
The geometry of this fracture (how easily and in what 
manner it fractures) is controlled by the food particles 
and not by the teeth since being structurally sound is 
selectively advantageous.  Understanding how foods 
prevent fracture is important for understanding tooth 
form.  Lucas spends what seems like a great deal of time 
discussing cusp shape (pointedness) and how this affects 
fracture propagation, cell toughness, and the fracture 
characteristics of various foods. However, in the end, one 
is left with a better understanding of how the structural 
characteristics of food can influence tooth shape so that 
structures such as marginal ridges are no longer perceived 
as accessory features of crown anatomy but as structures 
that facilitate fracture continuation.

With tooth size, Lucas prods us to view it as something 
whose variation is tied to the size of the entire orofacial 
complex, the size of which is, in turn, related to the size 
of the food that is put into it.  Stating that “The overriding 
philosophy is that physical properties of mammalian diets 
explain not only tooth size, but also the size of most orofacial 
structures” (p. 133), he proposes that tooth size should be 
scaled not to body size as in standard allometric analyses 
but to the size of the ‘food particles’ that they encounter.   
He finds that the size of the anterior teeth and that of the 
post-canine teeth are affected by different aspects of the 
diet.  On the one hand, jaw and anterior tooth size scale 
to the size of food as it is put into the mouth while post-
canine tooth size is related to external physical properties 
of the food and how it fractures.  Along the way Lucas 
presents in-depth discussions of the effects of variation 
in food toughness and tooth size, how food intake speed 
impacts overall orofacial size, and the differential effects 
of herbivory and carnivory on structures of the mouth.

Lucas explores tooth wear by examining what 
actually causes it.  From a mechanical standpoint tooth 
wear is the loss of small fragments from the body of the 
tooth, therefore, understanding how these fragments are 
removed is important.  Tooth-tooth wear (attrition) and 
food-tooth wear (abrasion) affect enamel and dentine in 
different ways resulting in different selective pressures 
on the structure of teeth. In this view, food-tooth wear 
impacts tooth size while enamel thickness responds to 
tooth-tooth wear.  The pressures of food-tooth interactions 
are spread across the whole of the crown and vary from 
chew to chew.  This impacts tooth size because the larger 
the tooth the more surface comes into contact with food 
which, in turn, increases the life of the tooth, impacting 
survival.  In contrast, tooth-tooth wear occurs repeatedly, 
and under high pressure, at very specific points, 
particularly the cusp tips, resulting in selective response 
in enamel thickness.  While Lucas states that he “did not 
say much in this chapter” (p. 200),  he does present a wide 
ranging discussion of tooth wear that includes several 
pages on the response of dentine, an area that is frequently 

overlooked.
The concluding chapter is self described as “a chapter 

of ideas, mixing fact with suggestions that, although 
seemingly logical and based on the previous chapters, 
might require a lifetime’s work to substantiate in any 
detail” (p. 202).  As speculative in nature as it is, this 
chapter is also a thorough overview at how teeth function 
and the evolution of the mammalian dentition in light 
of the emphasis on the fracture properties of food.  The 
last 20, or so, pages deals with diet and human evolution, 
touching on several areas.  An example or two will suffice.  
On page 238 Lucas anticipates the discovery of Homo 
floresiensis by suggesting that dental reduction, specifically 
tooth loss, could be tied to dental crowding brought on 
by dwarfing in small, isolated, mammalian populations.  
Pages 243-244 cover the molarization of premolars where 
he ties this trait to the size of the food that is being eaten 
and postulates that hominids who possess molarized 
premolars have adapted to eating relatively small objects.  
In fact it seems that Lucas relates everything in dental 
evolution to food toughness and particle size. For the 
most part this appears to work.  However, when it comes 
to applying this theoretical line to dental reduction and 
the effects of cooking food on tooth size Lucas completely 
ignores the possible impact agriculture and the resulting 
foods high in fermentable carbohydrates may have had 
in the selection for smaller, less complex, molars over the 
last 10,000 years.  

Now for a succinct concluding paragraph.  Hopefully 
this review has given the reader a hint at the complexity 
and value of Dental Functional Morphology.  Although “a 
little thick at times” (reviewer’s notes), if taken in the 
right dosage, with periods of contemplation liberally 
interspersed, one comes away with a new appreciation 
for the role food has played in the evolution of teeth.  
However technical the book may be at times, I think it can 
also become an important resource for professionals and 
as a starting point for discussion in graduate seminars.  
On a theoretical level most of what is proposed within this 
volume is well supported though it seems that Lucas is, at 
times, so tied to food particle size and fracture properties 
that other, simpler, possibilities are overlooked.  As in any 
book of this length there are several nit-picky things that 
I could address but I’ll only attack one.  On page 149, line 
4, in discussing characteristics of food Lucas says “Fleshy 
fruits are designed for feeding on by vertebrates because 
these animals can disperse their seeds effectively” 
(emphasis added).  The Darwinian in me recoils at the 
implications of some unseen hand working its magic in 
what is otherwise a fine evolutionary synthesis.  In the end, 
whether or not one buys Lucas’ premise that the evolution 
of the mammalian dentition is the result of adaptation to 
the mechanical properties of food this book is a valuable 
addition to the dental anthropology literature.

Review by
Greg C. Nelson