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EVOLUTIONARY ANATOMY OF THE PRIMATE CEREBRAL CORTEX
Edited by Dean Falk and Kathleen R. Gibson
Cambridge University Press
2001
FROM THE BACK COVER
Studies of brain evolution have moved rapidly in recent years, building on the
pioneering research of Harry J. Jerison. This book provides state-of-the-art
reviews of primate (including human) brain evolution. The book is divided into
two sections: the first gives new perspectives on the developmental,
physiological, dietary and behavioral correlates of brain enlargement. It has
long been recognized however, that brains do not merely enlarge globally as they
evolve, but that their cortical and internal organization also changes in a
process known as reorganization. Species-specific adaptations therefore have
neurological substrates that depend on more than just overall brain size. The
second section explores these neurological underpinnings for the senses,
adaptations and cognitive abilities that are important for primates. With a
prologue by Stephen J. Gould and an epilogue by Harry J. Jerison, this is an
important new reference work for all those working on brain evolution in
primates.
DEAN FALK is Professor of Anthropology and Adjunct Professor of Psychology at
the University at Albany, and an Honorary Professor of Anthropology at the
University of Vienna. Her research focuses on early hominids, primate brain
evolution, comparative neuroanatomy and the evolution of cognition, language and
intelligence. Her previous books include Braindance: New Discoveries about Human
Origins and Brain Evolution (1992) and Primate Diversity (2000).
KATHBEEN R. GIBSON is Professor and Chair of Basic Sciences at the University of
Texas, Houston, and Adjunct Professor of Anthropology at Rice University. She is
a member of the Executive Board of the American Anthropological Association. She
has also co-edited Language and 'Intelligence' in Monkeys and Apes (1990),
Tools, Language and Cognition in Human Evolution (1993), Mammalian Social
Learning(1999), Brain Maturation and Cognitive Development: Comparative and
Cross-Cultural Perspectives (1991), and Modelling the Early Human Mind (1996).
TABLE OF CONTENTS
List of contributors ix
Preface xii
Prologue Size matters and function counts xiii
STEPHEN JAY GOULD
Part I The evolution of brain size
Introduction to Part I 3
KATHBEEN R.GIBSON
1. Encephalization and its developmental structure: how many ways can a brain
get big? 14
PETER M. KASKAN & BARBARA L. FINLAY
2. Neocortical expansion and elaboration during primate evolution: a view from
neuroembryology 30 PASKO RAKIC & DAVID R. KORNACK
3. In defense of the Expensive Tissue Hypothesis 57
LESLIE C. AIELLO, NICOLA BATES & TRACEY JOFFE
4. Bigger is better: primate brain size in relationship to cognition 79
KATHLEEN R. GIBSON, DUANE RUMBAUGH & MICHAEL BERAN
5. The evolution of sex differences in primate brains 98
DEAN FALK
6. Brain evolution in hominids: are we at the end of the road? 113
MICHEL A. HOFMAN
Part II Neurological substrates of species-specific adaptations
Introduction to Part II 131
DEAN FALK
7. The discovery of cerebral diversity: an unwelcome scientific revolution 138
TODD M. PREUSS
8. Pheromonal communication and socialization 165
BRUNETTO CHIAREEEI
9. Revisiting australopithecine visual striate cortex: newer data from
chimpanzee and human brains suggest it could have been reduced during
australopithecine times 177
RALPH L. HOLLOWAY, DOUGLAS C. BROADFIELD & MICHAEL S. YUAN
10. Structural symmetries and asymmetries in human and chimpanzee brains 187
EMMANUEL GILISSEN
11. Language areas of the hominoid brain: a dynamic communicative shift on the
upper east side plenum 216
PATRICK J. GANNON, NANCY M. KHECK & PATRICK R. HOF
12. The promise and the peril in hominin brain evolution 241
PHILLIP V. TOBIAS
13. Advances in the study of hominoid brain evolution: magnetic resonance
imaging (MRI) and 3-D
Reconstruction 257
KATERINA SEMENDEFERI
14. Exo-and endocranial morphometrics in mid-Pleistocene and modern humans 290
KATRIN SCHAFER, HORST SEIDLER, FRED L. BOOKSTEIN, HERMANN PROSSINGER, DEAN FALK
& GLENN CONROY
Epilogue The study of primate brain evolution: where do we go from here? 305
HARRY J. JERISON
Index 333
PROLOGUE [Long but interesting] STEPHEN JAY GOULD
Size matters and function counts
Standard proverbs often give us no guidance because they come in contradictory
pairs, as in the relevant contrast for this preface: 'Fools rush in where angels
fear to tread' vs. 'Nothing ventured, nothing gained' or 'In for a penny, in for
a pound.' The best scientists try to balance these extremes by not wasting
precious time on the truly undoable and unanswerable, while remaining open
(indeed eager) to try the 'crazy' experiment that just might work. Science would
become stodgy and stymied if practitioners did not often risk the second part of
this pairing. (In one of the saddest 'science stories' I have ever heard,
developmental biologist Eddy de Robertis told me that, when he proposed his
utterly nutty, and brilliantly successful, experiment to search for homologs of
Drosophila homeobox genes in vertebrates, only two members of his lab refused to
participate for fear of being branded as fools - both graduate students. I do
understand that pressures for conformity may fall more strongly upon beginners
than upon established seniors. But if people won't think big and take risks at
the outset of their careers, how will they ever develop this most essential of
all habits among truly accomplished scientists?)
I met Harry Jerison in the early 1960s, when I was an undergraduate at Antioch
College, and he a scientist at a local research lab, and a professor. We were
both working - at the maximally disparate levels of undergraduate research
projects vs. professional papers - on the application of allometric equations
(power functions) to problems of growth and evolutionary size increase: I on the
domed shapes of land snail shells, he on the history of vertebrate brain sizes.
I thought, in all the arrogance of youth, that his bold project could never work
(whereas my petty, little contained study could at least be brought to rigorous
completion, albeit without earthshaking results). I had two major objections,
both recording the timidity of a tyro, to Jerison's procedures. First, why
should something so coarse and general as overall brain volume measure anything
of biological significance? Second, how (especially in fossils) could one hope
to get reliable measures in any case, especially for the independent variable of
body size required by the allometric analysis? I expressed my doubts to Harry,
and he had the courtesy, and professorial skill, to respond with bemusement, but
not derision or condescension - and to warn me about the dangers of stifling
prejudgment (a lesson I never forgot).
The results embodied Mark Twain's famous comment about his changing perceptions
of his father's mental capacities: that Twain, when in his late teens, had
considered his father a fool, but then, ten years later, became amazed as at how
much the old man had learned during the intervening decade. My snail studies
proceeded nicely and rightly; perhaps half a dozen people read the published
results. Harry's work culminated in one of the most influential books of the
late twentieth century organismal biology: Evolution of the Brain and
Intelligence, published in 1973 and still inspiring new thoughts and researches,
as this volume so directly and amply testifies.
Harry's work succeeded so brilliantly for two basic reasons (that I, as an
undergraduate, had been too inexperienced and generally sophomoric to
understand). First, Harry's methodology had been right and sophisticated for the
circumstances. Yes, size may seem too coarse to yield anything meaningful, but
how can you know until you try? And what else do you have to work with you, at
least for the fossil record, in any case? Science, as my favorite biologist and
essayist Peter Medawar wrote in a book title, is 'the art of the soluble.'
Better to try with something measurable and operational, however crude, than to
grouse at nature's recalcitrance and do nothing. Moreover, even if a measure of
volume does not record the desired mental property directly in se, size may
still serve us as well as an operational surrogate (and perhaps the only
accessible one at that) through its predictable correlation with the attribute
we seek to assess.
Second, Harry delivered the goods in a series of simple, robust and elegant
results. Two stand out in my memory. (1) Throughout the Tertiary, and within
broad taxa at a similar level of habitue and heritage, the log-log 'mouse to
elephant' interspecific curve of brain size vs. body size for mammalian species
maintains the same slope, but increases in y-intercept - thus yielding the same
proportional increase of brain size at any body size between two successive
curves through time. (2) Within this general pattern, sensible finer divisions
can be discerned. For example, the brain-body curve for carnivores lies higher
than that of their potential herbivorous prey at any common time, as does the
primate curve vs. the general curve for all mammals - also yielding the result
of a constant proportional advantage in brain size at any body size for
carnivores vs. herbivores and primates vs. averages for all other mammals.
As a student of the history of science, I must also confess my partisanship
towards Harry's formulation, and wry naming, of the 'encephalization quotient' -
or EQ in an obviously sardonic reference to the dubious IQ of our traditions for
assessing our own species - as the proper and best single number for expressing
brain size in an allometric world. Ever since Aristotle, scientists have known
that absolute brain size would not suffice, due to the correlation with body
size. Ever since Cuvier, scientists have understood that the simple brain/body
ratio wouldn't work either, due to negative allometry (and our resulting
unwillingness to declare shrews smarter than us). Ever since Dubois, scientist
have recognized that simple power functions could provide a good first
approximation for the allometric relationship. Thus, Jerison's EQ, or the ratio
of a particular creature's brain size to the expected brain size for its group
at its body size (as given by the allometric curve), embodies all these
refinements of more than two millennia of study.
As with any pathbreaking work based upon such an audacious methodology,
Jerison's results and procedures quickly became enmeshed in controversy - the
best of all criteria for recognizing fruitful scientific endeavors. I only
regret that our all-to-human propensity for dichotomization made the dispute
more acrimonious (and perhaps less productive, or at least less quickly
productive) than necessary - as too many participants parsed the issue as a
controversy between two extremes of evolution by pure size increase (based on a
view of the brain as a basically non-modular instrument acting as a coherent
entity despite any measured specializations of subregions), and evolution by
reorganization among constituent parts (based on the concept of a modular brain
with effectively independent regions of distinctly different function). I don't
think that any major participant ever held, or could hold, anything close to
either of these obviously extreme positions - but we do tend to so caricature
our adversaries in the heat of battle.
Perhaps Jerison did overemphasize Lashley's principle of mass action. (After
all, once one has decided to use a general measure - brain volume in this case -
even if only as a surrogate for estimating particulars of greater specificity
and localization, one may be excused for also citing, and perhaps even
exaggerating the importance or reliability, of the only coherent theoretical
defense ever offered for considering the general measure as a meaningful
biological property in itself as well.) but Jerison also, and consistently,
argued that he used general size measures as operational criteria, and as
estimators for desired properties, and not as direct assessments of mental
mights and powers. Moreover, he has always recognized that subparts of the brain
do not grow in isometry as the general mass increases. He has, for example,
emphasized, as a prominent theme and finding, the lack of correlation between
the size of the olfactory bulbs and that of other brain structures.
In any case, as Shakespeare noted, what's past is prologue. I think that this
controversy has been resolved at an appropriate golden mean, with devotees of
volume allowing a greater role for subtle reshuffling of sizes and spaces, and
especially for dramatic changes at the cellular level; and with devotees of
special qualities allowing that sizes, both absolute and relative, and of both
parts and wholes, yield important insights not obtainable by other means.
This remarkable book, appearing nearly 30 years after Jerison's pioneering
volume, proves the continuing vitality of the subject, and the importance of
Jerison's focus and prod. Moreover, the commingling of cellular with biometric
studies, and of growths and sizes of parts and wholes with research on
microarchitectural and cellular reorganization, testifies to the healing of past
controversies, and to a coordinated approach using the most fruitful themes of
both sides in a falsely perceived dichotomy.
As just one interesting and emblematic example of the need for such joint
approaches, and of complexities in interpretation, consider the finding of
Gannon et al., reported in this volume, that the differential enlargement of the
left plenum temporale, an asymmetry once viewed as distinctively human and
related to our unique capacity for language, also exists in apes, and perhaps in
Old World monkeys as well. The authors then inquire about the meaning of these
extended results: should we now claim that 'tine markedly asymmetric plenum
temporale is involved with ape "language" or other species specific,
interindividual communication modalities'? But the authors then realize that the
morphological similarity (and presumed homology) need not imply functional
identity. Perhaps this area operates differently in apes and humans? Perhaps we
have been wrong in assuming that the human asymmetry is 'involved with
high-level receptive language processing, but may simply represent an early
stage relay station'- in which case, we could more easily argue for functional
similarity in apes and humans, while revising our traditional hypothesis about
the actual function. In any case, we needed Jerisonian size date to make the
discovery itself, and we will need histological data on cellular reorganization
and experimental data on neurological operation to resolve the key issues about
function and evolutionary meaning.
In further examples of fruitful extensions from Jerison's methods and
approaches, Kaskan & Finlay proceed beyond Jerison's traditional bivariate
approach to apply multivariate factor analysis to volumes of neural structures
among species in several mammalian orders. In affirmation of Jerison's
conclusion about the relative independence of olfactory bulbs, they identify two
primary and orthogonal factors, with overall brain size (unsurprisingly) as the
focus of the much larger first factor (with most brain parts loading strongly on
this factor), but with a second factor dominated by olfactory and limbic
structures. Interestingly, whereas diurnal mammals tend to plot with high values
on the first factor, many nocturnal mammals may be distinguished by high
projections on the second factor, thus supporting a functional separation that
often transcends genealogical boundaries.
Further integration of metric and cellular or developmental approaches also
leads to insights about evolutionary mechanisms. Kaskan & Einlay find a
correlation between length of cytogenesis in embryonic development and areas of
the brain with largest relative increases as the entire structure grows.
Following this theme, Rakic & Kornack suggest that the cortical neuronal
precursor cells of the human brain may undergo three or four extra mitotic
divisions, in comparison with macaques. Both results suggest that the
evolutionary process of heterochrony, or changes in developmental timing for
structures already present in ancestors, may play a major role in restructuring
the brain by superintending changes in the relative sizes of parts as
consequences of differential rates of growth and cell division - yet another
example of interesting evolutionary hypotheses (large and meaningful outcomes
from potentially small and simple genetic impute in this case) exemplified by a
combination of metric and cellular approaches.
Harry Jerison, dear professor of my formative years, you are truly a work in
progress - as young as the new millennium, and as full of promise.
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