246 Evolutionary Anthropology BOOK REVIEWS umes, as well as what one finds in the simple idea that changes in the rate Whither the journals, falls within four major cate- and/or timing of specific developmen- gories, none of which is entirely inde- tal processes can cause many pheno- Evolution of Human pendent. First are studies of hetero- typic changes. Heterochrony has been chrony, how changes in the rate and both a boon and a curse ever since it Growth and timing of developmental processes was revived because it is so easily op- lead to evolutionary change. Hetero- erationalized and because it potentially Development? chrony research has a long history in explains how simple mechanisms can paleoanthropology. As is evident from account for large evolutionary shifts. Development, Growth and Evolution: Human Evolution through Develop- According to this framework, descen- Implications for the Study of the mental Change, which is mostly de- dants can differ from their ancestors by Hominid Skeleton Edited by P O’Higgins and M Cohn, voted to this subject, enthusiasm for altering the rate at which specific fea- (2000) Academic Press. 271 p. $79.95 studying heterochrony shows little tures grow, the length of time that they (cloth). ISBN 0-12-524965-9. sign of abating. Second, there has grow, or both. For example, many dif- been a recent interest in heterotopy, ferences cranial shape between humans Human Evolution through the study of evolutionary changes in and chimpanzees arise during ontog- Developmental Change spatial patterning. Heterotopy offers eny because the human brain grows Edited by N Minugh-Purvis and KJ McNamara (Eds) (2002) The Johns an interesting and important alterna- more rapidly and for longer than does Hopkins University Press. 508 p. $59.95 tive to heterochrony, but has barely the chimpanzee brain. Such cases of (cloth). ISBN 0-8018-6372-0. been considered in studies of human more development of a particular fea- evolution. Zelditch’s Beyond Hetero- ture during ontogeny in a descendant Beyond Heterochrony: The Evolution chrony includes many papers that test than in an ancestor are termed per- of Development heterotopy hypotheses, but none even amorphosis (or hypermorphosis). The Edited by ML Zelditch (ed) (2001) Wiley-Liss. 371 p. $99.95. ISBN 0-471- mentions human evolution, let alone opposite pattern, less development dur- 37973-5. primates. Third, and most prominent ing ontogeny in a descendant than in an of late, is evolutionary-developmental ancestor, is termed pedomorphosis (or These three recent volumes offer an biology, often called “evo-devo,” hypomorphosis). Peramorphosis and opportunity to evaluate current re- which is a partial focus of O’Higgins pedomorphosis are divided into further search in this field, especially in rela- and Cohn’s Development, Growth and subcategories, the most famous of tion to human evolution. After years Evolution. Evo-devo defies a simple which is neoteny, a type of pedomor- in which comparisons of adult skele- definition, but mostly concerns the phosis in which the juvenile form of an tal morphology dominated most re- study of the genetic bases for pheno- ancestor is retained in the adult stage of search on hominid systematics and typic shifts. Evo-devo is one of the the descendant. functional morphology, more and fastest growing and most prominent There is no question that hetero- more paleoanthropologists are turn- new fields of biology, largely because chrony is a powerful and often elegant ing to the study of growth and devel- of successes in explaining the regula- way of testing hypotheses about evo- opment to test their hypotheses. A tory bases for the origin of new body lutionary change. Human Evolution large proportion, though not all of this plans (bauplane). It is not surprising through Developmental Change con- research, is driven by the logic that that a number of researchers have at- tains excellent reviews of the assump- phenotypic shifts occur through alter- tempted to apply evo-devo studies tions and mathematical bases that un- ations of processes of growth and de- and, on occasion, approaches to phe- derlie heterochony analyses by D. velopment. It follows that to test hy- notypic shifts in human evolution. Fi- Alba, G. Eble, R. German and S. Stew- potheses about the nature and causes nally, a few researchers, myself in- art, B.K. Hall, K. McNamara, S. Rice, of evolutionary events it is necessary cluded, have been focusing on what and B. Shea. There are also a few good to test hypotheses about the shifts in one might call intermediate mecha- case studies (all of which have been processes of growth and development nistic processes, which lie somewhere published elsewhere in more detail). that generate novel phenotypes. Put between genetic studies and analyses Perhaps the most interesting is Mc- simply, the goal is to understand the of heterochrony. These approaches, Kinney’s work on the evolution of the processes that underlie the patterns along with papers on methodological brain. McKinney argues that the hu- we observe. issues, are also represented in Devel- man brain, as compared to that of The research presented in these vol- opment, Growth and Evolution. apes, evolved through two major per- So how are we doing? Let us start amorphotic changes. First, more cells with heterochrony, first formulated are allotted to the human brain early explicitly by Haeckel in 1866, and re- in development. Second, human vived almost single-handedly by the growth is characterized by a series of Evolutionary Anthropology 11:246–248 (2002) late Steven Jay Gould’s landmark sequential delays (called sequential DOI 10.1002/evan.10037 1 Published online in Wiley InterScience book, Ontogeny and Phylogeny. Het- hypermorphosis) in general somatic (www.interscience.wiley.com). erochrony analyses are based on the and neural mitosis. These delays gen- BOOK REVIEWS Evolutionary Anthropology 247 other taxa. Fascinating examples are presented in many chapters in the Zelditch volume, including those by Webster and coworkers, Zelditch and colleagues, Guralnik and Kurpius, Roopnarine, and Shapiro and Carl. These and other studies show that het- erotypy is also an important engine of change, even among such closely re- lated species as piranha fish. It will be fun to see such analyses extended more broadly to problems in human evolution, such as the chin. Chins de- Figure 1. Two examples of different ontogenetic vectors in shape space expected between velop, in part, from resorption fields ancestor (black) and descendant species. Left, paedomorphosis (hypomorphosis) versus on the upper alveolar surface of the paeramorphosis (hypermorphosis); Right, heterotopy. mandibular symphysis.3,4 Nonhuman primates lack this growth field, mak- erate longer durations of all develop- is the thorny problem of homology. ing the chin an excellent candidate for mental stages, a larger brain, and a Heterochrony analyses often homolo- heterotopy. larger body mass. In other words, a gize ontogenetic stages, but this can Another especially important devel- few ontogenetically early shifts that be theoretically or methodologically opment, and one that is of major inter- alter many aspects of phenotype and problematic, as is evident from analy- est to many biological anthropologists, life history can explain in one fell ses of the age of fossils such as Nari- is the application of three-dimensional swoop many of the differences be- okotome.2 Heterochrony studies also landmark coordinate data and geomet- tween humans (big-brained, big-bod- require the assumption that the mor- ric morphometrics to test alternative ied, and slow-growing) and both phological features one measures are hypotheses of evolutionary change. In chimpanzees and australopithecines homologous, independent units. This (small-brained, small-bodied, and fast assumption has bedeviled many stud- Development, Growth and Evolution, growing). Other interesting reviews of ies, which have failed to dissociate chapters by Spoor and colleagues and the application of heterochrony to hu- heterochronies between integrated re- by O’Higgins provide especially clear man evolution include chapters by C. gions. As Shea points out in Human and useful reviews of three-dimen- Berge and by L’Engle Williams and Evolution through Developmental sional imaging technology and the use colleagues. Change, studies of whether the human of three-dimensional data in geometric The advantages of heterochrony as a skull is globally neotenous are point- morphometrics. While geometric mor- methodology are also potential weak- less because the human skull com- phometric analyses of three-dimen- nesses. Heterochrony research is easy prises several regions that probably sional data are becoming increasingly to do, and if one accepts its assump- have quite different heterochronies. prevalent in the study of human evolu- tions uncritically, then one can always Our brains are obviously peramor- tion, they are not always used in the do analyses that yield results that are photic, but our faces may well be pe- context of explicit hypotheses about interpretable within a heterochrony domorphotic. A consequence of this growth and development. Yet, as Figure framework. All one needs to do is phenomenon is that analyses of inte- 1 shows, ontogenetic vectors from rela- measure some features in individuals grated morphologies can unwittingly tive warp analyses may be used to dis- of ancestor and descendant species of conflate dissociated heterochronies tinguish between heterotopy and het- different ages. (It is best if one knows as, for example, Lieberman shows for erochrony, and even to distinguish the real age and can avoid using size the brow ridge in Development, between some, but not all, of the sub- as a proxy for age). With a little data Growth and Evolution. categories of heterochrony. Applying entry and a smattering of computer A final problem is that while hetero- such a framework to recent geometric time, one can quickly calculate regres- chrony is clearly common, not all evo- morphometric studies in human evo- sion lines for two or more species hav- lutionary change is heterochronic.