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Life's devices: The physical world of animals and plants
TREE vol. 4, no. 6, June 1989
Where Are We All Going? Biological Aspects of Human Migration
edited by C.G.N. Mascie-Taylor and G.W. Lasker, Cambridge University Press (Cambridge Studies in Biological Anthropology No. 21, 7988. f30/ $54.50 (viii + 263 pages) ISBN 0521331099 Except for Africans, we are all recent immigrants to our native lands. Homo sapiens has migrated more extensively than any other large mammal, and the history of such movement can still be seen in the patterns of genetic relatedness among the peoples of the world. Anthropology is the study of the movement of people, of genes and of cultures. Until quite recently, these were all seen as the same thing; and for many years anthropologists were engaged in a futile search for the pure races once throught to have inhabited the continents and to have mixed to produce modern humans. This book is a successful attempt to rescue the study of migration from its own past. It deals with human restlessness, from the scale of recent migrations into cities to the global movements that led to man’s expansion over the past 50 000 years. There are many clues to past movements. Some societies keep a detailed account of their genetic history. On Tristan da Cunha, for example, information on immigration and emigration are good enough to show that the gene pool of the 300 or so modern inhabitants derives from only about a dozen founders who arrived on the island at various times in its 180-year history. The effective size of the Tristan population was greatly reduced by repeated losses through accident; and many migrant populations show similar periods of hardship during their move to a new home. Even during recent migrations to the New World, there were some voyages during which a third of the passengers died at sea. Although the high fertility of migrants once they reach their promised land may compensate for such losses, the echoes of past hardships still sound through the genetic structure of their descendants as many migrant populations possess only a sample of the genetic diversity present in their homeland. The first wave of migration to the Americas was across the Bering Land Bridge about 15000 years ago. The 19th century Eskimo migration into Greenland-during which only a few of the travellers, who were reduced to eating human flesh, survived - probably reflects the con-
ditions suffered by those first Americans. As a result of this population bottleneck, the extent of inherited variation in the modern aboriginal populations of the Americas is still much less than in the equivalent population of Australia, who, although much fewer in number, did not suffer a demographic crisis at their origin. Even on the small scale, migration has always been risky. There has been movement into cities for hundreds of years, but epidemics meant that no cities were self-sustaining until the 18th century. London in the time of Pepys was a town of about 100000, but it needed 5000 immigrants per year to maintain its population in the face of pestilence. Changing patterns of mortality among migrants faced with a new environment are still important clues as to the causes of disease, and there have been marked increases in, for example, the incidence of heart disease among Japanese immigrants into the United States and of diabetes among Samoans in New Zealand. Migrants can, nevertheless, adapt rapidly to their new home. There are changes of body size and proportions even among secondgeneration immigrants into developed countries. This flexibility of skeletal form may pose problems for those who try to reconstruct history by comparing the bones of past populations with those living today. This book does provide a wideranging account of human migration studies from a great diversity of fields. Some sections read slightly oddly to a population geneticist. It is hard to square the claim that ‘the case for a line from Sinanthropus to modern Mongoloids seems promis-
ing’ with the evidence from molecular biology (not mentioned here) that there are no human mitochondrial DNA lineages as old even as the Neanderthals. There is also a reiteration of the model of speciation now held almost exclusively by students of human evolution, but not necessarily wrong because of that that Homo sapiens originated simultaneously in several parts of the world. The book places rather little emphasis on modern studies of migration based on DNA haplotypes or on population genetic theory. There is much to be gained from combining classical studies of migration with molecular work. For example, the claim that Africans as a group form an evolutionary lineage distinct from the rest of the world is shown here to depend on DNA sequences from an African population that itself may not be representative of Africa as a whole because of its recent spread. Nevertheless, this book can be recommended to anyone interested in the history of human movement. It also deals with the future of humanity now that migration is so much more extensive than before. Many will be relieved to learn that even under the modern economic pressures forcing the movement of peoples within the United Kingdom, it will take 500 years to homogenize the genetic differences between England and Scotland. Only time will tell whether this period is also enough to remove the cultural differences that exist between the two countries. J.S. Jones Deptof Genetics andBiometry,UniversityCollege London,LondonNW1 2HE, UK
A Biomechanical Tour de Force Life’s Devices: The Physical World of Animals and Plants
by Steven Vogel, Princeton University Press, 1989. $49.50 hbk, $17.95 pbk (367 pages) ISBN 0 69108504 8 Calling themselves biomechanics, a small number of researchers have in recent years staged a renaissance in the field of comparative physiology. The question they ask is quite general - how do plants and animals work? Their viewpoint is that of an engineer - what are the mechanics of organisms and how have they been shaped by the evolutionary process? The burgeoning of bio-
mechanics has been fun to watch. As the expertise of the participants has expanded, the field has progressed from the simple, descriptive studies often associated with ‘functional morphology’, to a richer, experimental approach that is being applied to previously unexploited areas in physiology, paleontology and ecology. The field has benefited greatly from the writing ability of its participants. Introductory books such as those by McNeil1 Alexander’, Gordon*,3and Schmidt-Nielsen4 have served to spark interest in the mechanical view of life. But, successful as these and other texts have been in selling the biomechanical
187
TREE vol. 4, no. 6, June 7989
message to biologists, they are generally geared at a level too high to appeal to nonspecialists. With the exception of Gordon’s books, an awareness of calculus is assumed, and a basic background in biology is very helpful. As a result, the biomechanical approach has been largely beyond the reach of the average student in the Arts. Therein lies the impetus for this latest addition to the biomechanical bookshelf. For the past 20 years Steven Vogel has produced an offbeat series of papers on the interaction between the dynamics of fluids and the functions of plants and animals: lift and drag of fruit fly wings, induced flow through gopher burrows and sponges, passive refilling of squids and scallops. In 1981 he synthesized much of the available literature on biological fluid mechanics in a readable, often humorous, text entitled Life In Moving Fluid@. The book serves as a companion to Mechanical Design in OrganismsG by Wainwright et a/., and by covering, respectively, the biological mechanics of fluids and of solids, the two have become the ‘bibles’ of the field. In Life’s Devices, Vogel applies his unique perspective to the task of presenting biomechanics to nonspecialists. The subject matter is much the same as that covered by the ‘bibles’ -the mechanics of solids and fluids, with the addition of chapters on diffusion, scaling and heat -
but very little is assumed in the way of background. For example, a footnote on the first page carefully explains what the text citation of an author and date means and where the bibliography can be found. No facility with mathematics is assumed beyond simple algebra (and even this is reviewed in an appendix). The subject matter is clearly and delightfully presented. Each physical concept - from viscosity, gas laws and diffusion to beam theory, fracture mechanics and hydraulics - is explained in the context of biological examples. In many cases, simple demonstrations are suggested, of the sort that can be performed in one’s kitchen. Vogel’s joy in explaining his science is apparent on every page, and this as much as anything else will ensure the success of the text. The author’s ability to turn an alliterative phrase is rivalled only by that of Stephen Jay Gould, as is his use of a broad vocabulary. Life’s Devices is not without its quirks. The most important is Vogel’s decision to avoid the concept of energy. As justification, he cites R.P. Feynman’s admission7 that ‘we have no knowledge of what energy is’. Feynman, however, did not allow this to stop him from exploiting the exceptional utility of the concept. Vogel does, and there are several cases in which his explanations could be substantially condensed (and thereby improved) by simple
reference to the conservation of energy. But the absence of energy as a unifying concept is a quirk rather than a flaw, conspicuous only to those who already have a background in physics. On the whole Life’s Devices admirably achieves its goals. Not only does it fill a useful niche in presenting biomechanics to a new audience, it is a delightful and insightful read for any biologist.
Mark W. Denny Hopkins Marine Station, Dept of Biological Sciences, StanfordUniversity, PacificGrove,CA63966-3694, USA
Referewes 1 Alexander, R. McN. (1983) Animal Mechanics (2nd edn), Blackwell Scientific Publications 2 Gordon, J.E. (1978) Structures: or Why Things Don’t FaN Down, Penguin Books 3 Gordon, J.E. (1988) The NewScience of Strong Materials, Penguin Books 4 Schmidt-Nielsen, K. (1984) Scaling: Why Animal Size Is So important, Cambridge University Press 5 Vogel, S. (1981) Life in Moving Fluids, Princeton University Press 6 Wainwright, S.A.,.Biggs, W.D., Currey, J.D. and Gosline. J.M. (1976) Mechap;on/ Design in,Orga&ms, Princeton University Press 7 Feynman, R.P., Leighton, R.B. and Sands, M. (1963) The Feynman Lectures on Physics (Vol. 11, Addison-Wesley Publishing Company 6 Timoshenko, T.P. and Gere, J.M. (1972) Mechanics of Materials, Van Nostrand ,,,“.-,
New Perspectives in Plant Evolution and the population PlantEvolutionary Biology was written, genetic and ecological perspective that he described then has become central to the study of plant evoledited by Leslie D. Gottlieb and ution. In addition, rapid advances in Subodh K. Jain, Chapman & Hall, molecular biology have opened new 1988. f45 hbk, f22.50 pbk (xv + 474 fields of evolutionary inquiry, and pages) ISBN 0 412 29300 5 have provided tools for addressing questions of both pattern and proIn 1974, G. Ledyard Stebbins wrote cess. Just how far plant evolutionary Plants: in the preface to Nowering biology has come - and how far it Evolution above the Species Level’ : has yet to go toward achieving a true One of my major objectives is to synthesis-is evident from this book, find out to what extent both phywhich stems from a 1986 symlogeny itself and the methods of posium honoring over 50 years of gaining new information about evolutionary history will be modicontributions by Professor Stebbins. fied if botanists shift their major Given the enormous diversity of emphasis away from traditional subjects that fall under the heading and idealistic mortaxonomy of ‘evolutionary biology’, no single phology, and toward population volume of contributed papers could and developmental genetics, combe expected to achieve full coverage. parative developmental physiThough basically microevolutionary ology, and an ecological viewpoint in emphasis, this book does contain that places primary emphasis upon some chapters of a more phylogeninteractions between populations and their environment. etic nature. One area conspicuously Fifteen years have passed since that absent, however, is paleobotany. 188
This is unfortunate, because the fossil record has in recent years become an increasingly valuable evolutionary tool, both through new discoveries and by the application of rigorous analytical methods to comparisons between extinct and extant taxa. The 14 chapters are organized into six parts, separated by editors’ commentaries that provide continuity and often point out the potential value of molecular biology to issues of that section. This is especially true in the commentary following the first of the contributed parts, a diverse section consisting of three chapters with an organismal focus (P.H. Raven; R. Wyatt; C. Rick) and two that review the structure and evolutionary dynamics of plant organellar (C.W. Birky) and nuclear (S.D. Tanksley and E. Pichersky) genomes. The complexity of molecular evolution described in these latter chapters should give pause for thought to
Where Are We All Going? Biological Aspects of Human Migration
edited by C.G.N. Mascie-Taylor and G.W. Lasker, Cambridge University Press (Cambridge Studies in Biological Anthropology No. 21, 7988. f30/ $54.50 (viii + 263 pages) ISBN 0521331099 Except for Africans, we are all recent immigrants to our native lands. Homo sapiens has migrated more extensively than any other large mammal, and the history of such movement can still be seen in the patterns of genetic relatedness among the peoples of the world. Anthropology is the study of the movement of people, of genes and of cultures. Until quite recently, these were all seen as the same thing; and for many years anthropologists were engaged in a futile search for the pure races once throught to have inhabited the continents and to have mixed to produce modern humans. This book is a successful attempt to rescue the study of migration from its own past. It deals with human restlessness, from the scale of recent migrations into cities to the global movements that led to man’s expansion over the past 50 000 years. There are many clues to past movements. Some societies keep a detailed account of their genetic history. On Tristan da Cunha, for example, information on immigration and emigration are good enough to show that the gene pool of the 300 or so modern inhabitants derives from only about a dozen founders who arrived on the island at various times in its 180-year history. The effective size of the Tristan population was greatly reduced by repeated losses through accident; and many migrant populations show similar periods of hardship during their move to a new home. Even during recent migrations to the New World, there were some voyages during which a third of the passengers died at sea. Although the high fertility of migrants once they reach their promised land may compensate for such losses, the echoes of past hardships still sound through the genetic structure of their descendants as many migrant populations possess only a sample of the genetic diversity present in their homeland. The first wave of migration to the Americas was across the Bering Land Bridge about 15000 years ago. The 19th century Eskimo migration into Greenland-during which only a few of the travellers, who were reduced to eating human flesh, survived - probably reflects the con-
ditions suffered by those first Americans. As a result of this population bottleneck, the extent of inherited variation in the modern aboriginal populations of the Americas is still much less than in the equivalent population of Australia, who, although much fewer in number, did not suffer a demographic crisis at their origin. Even on the small scale, migration has always been risky. There has been movement into cities for hundreds of years, but epidemics meant that no cities were self-sustaining until the 18th century. London in the time of Pepys was a town of about 100000, but it needed 5000 immigrants per year to maintain its population in the face of pestilence. Changing patterns of mortality among migrants faced with a new environment are still important clues as to the causes of disease, and there have been marked increases in, for example, the incidence of heart disease among Japanese immigrants into the United States and of diabetes among Samoans in New Zealand. Migrants can, nevertheless, adapt rapidly to their new home. There are changes of body size and proportions even among secondgeneration immigrants into developed countries. This flexibility of skeletal form may pose problems for those who try to reconstruct history by comparing the bones of past populations with those living today. This book does provide a wideranging account of human migration studies from a great diversity of fields. Some sections read slightly oddly to a population geneticist. It is hard to square the claim that ‘the case for a line from Sinanthropus to modern Mongoloids seems promis-
ing’ with the evidence from molecular biology (not mentioned here) that there are no human mitochondrial DNA lineages as old even as the Neanderthals. There is also a reiteration of the model of speciation now held almost exclusively by students of human evolution, but not necessarily wrong because of that that Homo sapiens originated simultaneously in several parts of the world. The book places rather little emphasis on modern studies of migration based on DNA haplotypes or on population genetic theory. There is much to be gained from combining classical studies of migration with molecular work. For example, the claim that Africans as a group form an evolutionary lineage distinct from the rest of the world is shown here to depend on DNA sequences from an African population that itself may not be representative of Africa as a whole because of its recent spread. Nevertheless, this book can be recommended to anyone interested in the history of human movement. It also deals with the future of humanity now that migration is so much more extensive than before. Many will be relieved to learn that even under the modern economic pressures forcing the movement of peoples within the United Kingdom, it will take 500 years to homogenize the genetic differences between England and Scotland. Only time will tell whether this period is also enough to remove the cultural differences that exist between the two countries. J.S. Jones Deptof Genetics andBiometry,UniversityCollege London,LondonNW1 2HE, UK
A Biomechanical Tour de Force Life’s Devices: The Physical World of Animals and Plants
by Steven Vogel, Princeton University Press, 1989. $49.50 hbk, $17.95 pbk (367 pages) ISBN 0 69108504 8 Calling themselves biomechanics, a small number of researchers have in recent years staged a renaissance in the field of comparative physiology. The question they ask is quite general - how do plants and animals work? Their viewpoint is that of an engineer - what are the mechanics of organisms and how have they been shaped by the evolutionary process? The burgeoning of bio-
mechanics has been fun to watch. As the expertise of the participants has expanded, the field has progressed from the simple, descriptive studies often associated with ‘functional morphology’, to a richer, experimental approach that is being applied to previously unexploited areas in physiology, paleontology and ecology. The field has benefited greatly from the writing ability of its participants. Introductory books such as those by McNeil1 Alexander’, Gordon*,3and Schmidt-Nielsen4 have served to spark interest in the mechanical view of life. But, successful as these and other texts have been in selling the biomechanical
187
TREE vol. 4, no. 6, June 7989
message to biologists, they are generally geared at a level too high to appeal to nonspecialists. With the exception of Gordon’s books, an awareness of calculus is assumed, and a basic background in biology is very helpful. As a result, the biomechanical approach has been largely beyond the reach of the average student in the Arts. Therein lies the impetus for this latest addition to the biomechanical bookshelf. For the past 20 years Steven Vogel has produced an offbeat series of papers on the interaction between the dynamics of fluids and the functions of plants and animals: lift and drag of fruit fly wings, induced flow through gopher burrows and sponges, passive refilling of squids and scallops. In 1981 he synthesized much of the available literature on biological fluid mechanics in a readable, often humorous, text entitled Life In Moving Fluid@. The book serves as a companion to Mechanical Design in OrganismsG by Wainwright et a/., and by covering, respectively, the biological mechanics of fluids and of solids, the two have become the ‘bibles’ of the field. In Life’s Devices, Vogel applies his unique perspective to the task of presenting biomechanics to nonspecialists. The subject matter is much the same as that covered by the ‘bibles’ -the mechanics of solids and fluids, with the addition of chapters on diffusion, scaling and heat -
but very little is assumed in the way of background. For example, a footnote on the first page carefully explains what the text citation of an author and date means and where the bibliography can be found. No facility with mathematics is assumed beyond simple algebra (and even this is reviewed in an appendix). The subject matter is clearly and delightfully presented. Each physical concept - from viscosity, gas laws and diffusion to beam theory, fracture mechanics and hydraulics - is explained in the context of biological examples. In many cases, simple demonstrations are suggested, of the sort that can be performed in one’s kitchen. Vogel’s joy in explaining his science is apparent on every page, and this as much as anything else will ensure the success of the text. The author’s ability to turn an alliterative phrase is rivalled only by that of Stephen Jay Gould, as is his use of a broad vocabulary. Life’s Devices is not without its quirks. The most important is Vogel’s decision to avoid the concept of energy. As justification, he cites R.P. Feynman’s admission7 that ‘we have no knowledge of what energy is’. Feynman, however, did not allow this to stop him from exploiting the exceptional utility of the concept. Vogel does, and there are several cases in which his explanations could be substantially condensed (and thereby improved) by simple
reference to the conservation of energy. But the absence of energy as a unifying concept is a quirk rather than a flaw, conspicuous only to those who already have a background in physics. On the whole Life’s Devices admirably achieves its goals. Not only does it fill a useful niche in presenting biomechanics to a new audience, it is a delightful and insightful read for any biologist.
Mark W. Denny Hopkins Marine Station, Dept of Biological Sciences, StanfordUniversity, PacificGrove,CA63966-3694, USA
Referewes 1 Alexander, R. McN. (1983) Animal Mechanics (2nd edn), Blackwell Scientific Publications 2 Gordon, J.E. (1978) Structures: or Why Things Don’t FaN Down, Penguin Books 3 Gordon, J.E. (1988) The NewScience of Strong Materials, Penguin Books 4 Schmidt-Nielsen, K. (1984) Scaling: Why Animal Size Is So important, Cambridge University Press 5 Vogel, S. (1981) Life in Moving Fluids, Princeton University Press 6 Wainwright, S.A.,.Biggs, W.D., Currey, J.D. and Gosline. J.M. (1976) Mechap;on/ Design in,Orga&ms, Princeton University Press 7 Feynman, R.P., Leighton, R.B. and Sands, M. (1963) The Feynman Lectures on Physics (Vol. 11, Addison-Wesley Publishing Company 6 Timoshenko, T.P. and Gere, J.M. (1972) Mechanics of Materials, Van Nostrand ,,,“.-,
New Perspectives in Plant Evolution and the population PlantEvolutionary Biology was written, genetic and ecological perspective that he described then has become central to the study of plant evoledited by Leslie D. Gottlieb and ution. In addition, rapid advances in Subodh K. Jain, Chapman & Hall, molecular biology have opened new 1988. f45 hbk, f22.50 pbk (xv + 474 fields of evolutionary inquiry, and pages) ISBN 0 412 29300 5 have provided tools for addressing questions of both pattern and proIn 1974, G. Ledyard Stebbins wrote cess. Just how far plant evolutionary Plants: in the preface to Nowering biology has come - and how far it Evolution above the Species Level’ : has yet to go toward achieving a true One of my major objectives is to synthesis-is evident from this book, find out to what extent both phywhich stems from a 1986 symlogeny itself and the methods of posium honoring over 50 years of gaining new information about evolutionary history will be modicontributions by Professor Stebbins. fied if botanists shift their major Given the enormous diversity of emphasis away from traditional subjects that fall under the heading and idealistic mortaxonomy of ‘evolutionary biology’, no single phology, and toward population volume of contributed papers could and developmental genetics, combe expected to achieve full coverage. parative developmental physiThough basically microevolutionary ology, and an ecological viewpoint in emphasis, this book does contain that places primary emphasis upon some chapters of a more phylogeninteractions between populations and their environment. etic nature. One area conspicuously Fifteen years have passed since that absent, however, is paleobotany. 188
This is unfortunate, because the fossil record has in recent years become an increasingly valuable evolutionary tool, both through new discoveries and by the application of rigorous analytical methods to comparisons between extinct and extant taxa. The 14 chapters are organized into six parts, separated by editors’ commentaries that provide continuity and often point out the potential value of molecular biology to issues of that section. This is especially true in the commentary following the first of the contributed parts, a diverse section consisting of three chapters with an organismal focus (P.H. Raven; R. Wyatt; C. Rick) and two that review the structure and evolutionary dynamics of plant organellar (C.W. Birky) and nuclear (S.D. Tanksley and E. Pichersky) genomes. The complexity of molecular evolution described in these latter chapters should give pause for thought to