EVOLUTIONARY BIOLOGY
Evolutionary biology provides the key to understanding the principles governing the origin and extinction of species. It provides causal explanations, based on history and on processes of genetic change and adaptation, for the full sweep of biological phenomena, ranging from the molecular to the ecological. Thus, evolutionary biology allows us to determine not only how and why organisms have become the way they are, but also what processes are currently acting to modify or change them.
Response to change is a feature of evolution that is becoming increasingly important in terms of scientific input into societal issues. We live in a world that is undergoing constant change on many levels, and much of that change is a direct consequence of human activity. Evolutionary biology can contribute explicitly to enhanced awareness and prediction of mid and long term consequences of environmental disturbances, whether they be deforestation, application of pesticides, or global warming.
Distinctive perspectives on biology offered by evolutionary biology include emphasis on the interplay between chance and adaptation as conflicting agents of biological change, on variation as an inherent feature of biological systems, and on the importance of biological diversity. Variation is a key concept, since evolutionary change ultimately depends on the differential success of competing genetic lineages. The ultimate consequence of variation and evolutionary divergence is biological diversity.
Biological species are not fixed entities, but rather are subject to ongoing modification through chance or adaptation. Understanding why and how some species are able to change apace with new environmental challenges is critical to the sustainability of human endeavor.
What Does the Future Hold for Evolutionary Biology?
In contrast to some other biological disciplines such as biochemistry and ecology, in which applications to health or environmental science are emphasized in training and research, the development of an explicit field of "applied evolutionary biology" is only beginning.
The history of evolutionary biology shows that beneficial interactions between basic and applied research can flow in both directions. Evolutionary genetics has profited from genetic research aimed at improving crops and domesticated animals. Studies of mutational changes in the metabolic capacities of microorganisms, pursued in part because of their industrial applications, have shed light on the evolution of biochemical pathways. Genetic and phylogenetic studies of corn and other crops have provided insight into rates of evolution and changes in developmental pathways.
The study of sickle-cell hemoglobin and other polymorphisms in humans has provided some of the best analyses of modes of natural selection. The evolution of pesticide and drug resistance in insect pests, weeds, rats, and pathogenic bacteria, the evolution of life history characteristics in overexploited fish populations and introduced insect pests, the evolution of virulence in viruses and bacteria, and coevolution between insects and plants have been subjects of some of the best case studies of evolutionary dynamics.
Evolutionary Biologists can often address basic questions by working on systems that are directly relevant to societal needs. To be sure, the ideal systems for addressing certain basic intellectual problems will often not be those with immediate social utility, although it is often hard to predict in advance what questions in basic science will lead to useful breakthroughs. Moreover, we reiterate the importance of exploring and understanding the diversity of organisms as an intellectual goal, in light of some of the payoffs discussed above.
But in many cases, research on a socially relevant organism or system can both advance basic science and contribute to societal needs. We anticipate that evolutionary biologists will increasingly play these dual roles.
It is important to emphasize that much of the expected progress in applied evolutionary biology will require, and be inseparable from, progress in basic research. As in other biological disciplines, studies of model organisms and systems (including not only standard laboratory species such as yeasts, Drosophila, and Arabidopsis, but also a variety of wild species) will provide insights that can be applied to societal needs. Likewise, conceptual and theoretical advances in basic evolutionary biology will contribute to progress in applied evolutionary biology. Important progress will be made in the areas of health science, agriculture and other biological resource management, natural products, environment and conservation, technology development, and educational and intellectual interchange with other scholarly disciplines and with the general public.
1. Health Science
Advances in applying evolutionary disciplines to human health fall into several categories.
· Genetic Identification. Population genetics has developed, and is continuing to improve, analytical methods for identifying individuals and relationships among individuals from a profile of genetically variable markers.
· Evolutionary Developmental Genetics. Comparative data on the genetic and mechanical bases of development in diverse vertebrates and other organisms will shed much light on the mechanisms of human development. Such studies will contribute to our understanding of the bases of hereditary and other congenital defects in humans, and may ultimately be useful in developing gene therapies.
· Mechanisms and Evolution of Antibiotic Resistance. Genetic, phylogenetic, and comparative biochemical studies of bacteria, protists, fungi, helminths, and other parasites will help to identify targets for antibiotics.
· Parasite Virulence and Host Resistance. Evolutionary studies of parasite/host interactions, using both model systems and human parasites and pathogens, are only beginning to determine the conditions that lead parasites to become more virulent or more benign.
· Epidemiology and Evolutionary Ecology of Pathogens and Parasites. New and resurgent diseases have emerged as major threats to public health, and more will probably do so in the future. Evolutionary biologists can aid in the effort to counter these threats in several ways.
2. Agriculture and Biological Resources
We noted above the many ways in which evolutionary biology has had an intimate relationship with agriculture and the management of biological resources such as forests and fisheries. The scope for further contributions in these areas is enormous. We highlight only a few of the most important topics to be pursued.
· Pesticide resistance. Despite new alternative methods of pest management, judicious use of pesticides will undoubtedly remain indispensable. The evolution of pesticide resistance in insects, nematodes, fungi, and weeds is a serious economic problem that should receive major attention.
· Alternatives in Pest Management. Evolutionary considerations will be important in evaluating many alternative methods of pest management, such as mixing different crops or crop varieties (intercropping), or developing transgenic crops that carry resistance factors protecting them against insects or other pests. It will be important to analyze the physiological effects of natural resistance factors on pest organisms, the mechanisms by which some insects and fungi overcome their effects, and genetic variation in the responses of target species to natural resistance factors.
· Genetic Diversity in Economically Important Organisms. Evolutionary and agricultural scientists together will use QTL (quantitative trait loci) mapping and other methods to locate the genes for, and elucidate the mechanistic bases of, important plant traits, such as resistance to pathogens and to environmental stresses. Such studies will also serve the interests of basic scientists interested in the adaptations of plants to environmental factors.
· Fisheries. Several kinds of evolutionary studies have been and will continue to be important in managing commercial and sport fisheries. Molecular genetic markers will aid researchers in distinguishing breeding populations and migration routes of species such as cod and salmon. Studying the evolution of life history characteristics such as growth rate and age at maturity will enable managers to evaluate the genetic and demographic effects of harvesting on fish populations.
3. Natural Products and Processes
Pharmaceutical and other industries are actively searching for novel products and processes by screening plants, animals, and microorganisms. Because of its commercial implications, the search for and development of novel products and processes raises serious issues in patent law, international law, and the publication of scientific data that are beyond the scope of this report, but which will affect the engagement and activities of research scientists. Evolutionary studies will greatly contribute to research and development, resulting in many novel products and processes.
· Systematics and Phylogeny. Documenting the diversity of potentially useful organisms is the foundation for all further work. The phylogenetic aspect of systematics is crucial for pointing researchers toward species that are related to those in which potentially useful compounds or metabolic pathways have been found, since related species may have similar, perhaps even more efficacious, properties. The systematics of bacteria, protists, fungi, and other inconspicuous organisms are very poorly known and require extensive investigation.
· Studies of Adaptation. Antibiotics, resistance factors for use in transgenic crops, and other useful natural products are likely to be found by studying the chemical mechanisms of competition among fungi and microorganisms, the defenses of plants against their natural enemies, and the waxes, steroids, terpenes, hormones, and innumerable other compounds that organisms use for diverse adaptive ends.
· Genetic and Physiological Studies. Industry anticipates that "great advances in bio-processing can be expected from future exploration of the yet unexplored biodiversity of the land and sea". Yet most microorganisms have not yet been described and characterized, the physiological capacities of most of them are unknown, and there is little information available on their genetic diversity, or on what kinds of novel metabolic capacities can arise by mutation. Researchers trained in evolutionary genetics, physiology, and systematics will make important contributions to this area.
4. Environment and Conservation
Evolutionary principles are immediately applicable to the conservation of rare and endangered species and ecosystems; in fact, many leading conservation biologists have done research in basic evolutionary biology. Evolutionary biology can also shed light on environmental management issues that bear directly on human health and welfare. Here I'm goanna highlight only a few of the needs for evolutionary study in the fields of environmental management and conservation.
· Bioremediation. Bioremediation refers primarily to the use of organisms (especially bacteria and plants) in cleaning up spills and toxins, treating sludge, and restoring degraded soils. Evolutionary biology can contribute to bioremediation by identifying species or genetic strains with desirable properties, by understanding the agents of natural selection that give rise to such properties, and by identifying the conditions that favor the persistence of useful organisms.
· Unplanned Introductions. The advent of genetic engineering has caused concern about the escape of vigorous, genetically novel microorganisms, plants, fishes, or other organisms, and about the possibility that genes for novel capacities could spread by hybridization from transgenic organisms into wild ones, transforming benign species into novel pests. Evolutionary biologists have been active in assessing such risks.
· Predicting Effects of Environmental Change. Of the many effects human activities have on the environment, the most universal posssible effect is global warming. Many other environmental alterations, such as desertification, salinization of fresh water, and acid rain, have more local, but still profound, effects on both wild species and biological resources. Predicting and possibly forestalling the effects of such changes is an important goal for ecological studies, but evolutionary biology also faces major challenges. In particular, we need to understand far better the conditions under which populations adapt to environmental changes versus migrating or becoming extinct, and what kinds of species will follow these courses. We also need to understand the conditions favoring "breakouts," in which new species adapt to and disperse rapidly into novel environments.
· Conservation of Biodiversity. Alteration of habitats, intentional and unintentional harvesting of natural populations, and other human activities constitute a grave threat to the persistence of many species. Inevitably, difficult choices will be necessary in the allocation of resources, and not all threatened species and ecosystems will be safeguarded. Evolutionary biology and ecology work hand-in-hand in addressing these issues.
Technology Development
In all sciences, the need to solve problems stimulates the development of new techniques and technologies. As noted earlier, most of the broadly applicable technologies that have been developed at least partly due to the need to solve evolutionary problems have been in the areas of statistics, computation, and data management. We anticipate that as evolutionary biology addresses ever more complex problems and richer data sets, collaborations among evolutionary biologists will lead to further technical innovations in these areas. Some likely areas of progress will be the analysis of the dynamics of complex, nonlinear systems; optimal search routines—e.g., for phylogenetic tree structures; evolutionary computation—i.e., development of “evolving” algorithms for efficient problem solving; and applications in computer-based artificial intelligence and artificial life.
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HOW DOES EVOLUTIONARY BIOLOGY CONTRIBUTE TO SOCIETY
The many subdisciplines of Evolutionary Biology have made innumerable contributions to meeting societal needs.
Human Health and Medicine
1. Genetic Disease
Genetic diseases are caused by variant genes or chromosomes, although the expression of such conditions often is influenced by environmental (including social and cultural) factors and by an individual’s genetic constitution at other loci. To the many medical diseases caused by genetic variants, we can add many common conditions associated with old age, significant components of learning disabilities, and behavioral disorders, all of which contribute to human suffering and demand medical, educational, and social services resources. Each of these genetic disorders is caused by alleles at one or more genetic loci, which range in frequency from very rare to moderately common (such as the alleles for sickle-cell disease and cystic fibrosis, which are rather frequent in some populations). Allele frequencies are the subject of population genetics, which can be readily applied to two tasks: determining the reasons for the frequency of a deleterious allele, and estimating the likelihood that a person will inherit the allele or develop the trait.
Thus, for example, the high frequency of alleles for sickle-cell and several other defective hemoglobins in some geographic locations signaled to population geneticists that some agent of natural selection probably maintained these alleles in populations. Their geographic distribution suggested an association with malaria, and subsequent research confirmed that these alleles are prevalent because heterozygous carriers have greater resistance to malaria. This is a clear illustration of the theory, developed by evolutionary biologists decades before the sickle-cell pattern was described, that a heterozygous fitness advantage can maintain deleterious alleles in populations.
It can be important to couples to know the likelihood that their children will inherit genetic diseases, especially if these have occurred in their family history. Genetic counseling has provided such advice for many decades. Genetic counseling is applied population genetics, for it relies on both pedigree analysis (standard genetics) and knowledge of the frequency of a particular allele in the population at large to calculate the likelihood of inheriting a genetic defect. Likewise, evaluating the health consequences of marriage among related individuals or of increased exposure to ionizing radiation and other environmental mutagens depends critically on theories and methods developed by population geneticists.
Molecular biology is revolutionizing medical genetics. The technology now exists to locate genes and determine their sequence in the hope of determining the functional difference between deleterious and normal alleles. Carriers of deleterious alleles can be identified from small samples of DNA (including those obtained by amniocentesis), and genetic therapy, whereby normal alleles can be substituted for defective ones, is a real possibility. Methods and principles developed by evolutionary biologists have contributed to these advances, and are likely to make other contributions in the future. Locating a gene for a particular trait, for instance, is no easy task. The process relies on associations between the gene sought and linked genetic markers (e.g., adjacent genes on the same chromosome). The consistency of association of an allele with such markers—the likelihood that a marker on any one person's chromosome will signal the presence of a deleterious allele in its vicinity—is the degree of "linkage disequilibrium." Population genetics theory has been developed to predict the degree of linkage disequilibrium as a function of such factors as allele frequencies, recombination rates, and population size. This theory was instrumental in one of the first cases in which a common deleterious allele—the one causing cystic fibrosis—was located and subsequently sequenced. As the effort to realize the promised rewards of the Human Genome Project moves forward, the role played by theories from population genetics will grow.
Determining which of the many nucleotide differences between a deleterious allele and a normal allele causes a disease is important for understanding how its effects may be remedied. Molecular evolutionary studies have given rise to several methods that can help to distinguish variation in a gene sequence that strongly affects fitness (by affecting function) from variation that is relatively neutral. These methods employ analyses of DNA sequence variation both within species and among closely related species. We predict that these methods, including comparisons among human genes and their homologues in other primates, will help to identify the variations that cause genetic diseases.
2. Systemic Disease
All genetic diseases collectively affect only about 1% of the human population. In contrast, more and more human disease and death is associated with chronic systemic diseases, such as coronary artery disease, stroke, hypertension, and Alzheimer's disease. These diseases emerge from a complex set of interactions between genes and environment. This complexity makes it difficult to study the linkage between genes and systemic disease. Evolutionary principles and approaches have already had a major impact on the study of this linkage. For example, some genes, because of their known biochemical or physiological functions, can be identified as "candidate genes" for contributing to a systemic disease.
However, there is so much molecular genetic variation at these candidate loci in the general human population that it is finding the specific variants associated with disease risk is akin to the proverbial search for the needle in the haystack. Evolutionary phylogenetic techniques can be used to estimate a gene tree from this genetic variation. Such a gene tree represents the evolutionary history of the genetic variants of the candidate gene. If any mutation has occurred during evolutionary history that has altered risk for a systemic disease, then the entire branch of the gene tree that bears that mutation should show a similar disease association.
Gene tree analyses have already been successfully used to discover genetic markers that are predictive of risk for coronary artery disease, risk for Alzheimer's disease, and the response of cholesterol levels to diet. Moreover, evolutionary analyses of gene trees can help to identify the mutation that actually causes the significant health effect, critical first step in understanding the etiology of the disease and in designing possible treatments. As more candidate genes for common systemic diseases are identified there will be a greater need for evolutionary analyses in the future.
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Public Understanding of Science
Important challenges for evolutionary biology lie not only in the domain of research, but also in the domain of public understanding and appreciation of science, which is necessary both for the support of research and for the awareness and understanding an educated citizenry requires in an increasingly scientific and technological age.
Many surveys of students and the general public have shown that the United States ranks relatively low among industrial nations in their command of science and mathematics. This is a matter of serious concern to all scientific disciplines and, indeed, to all agencies and organizations concerned with the future of the country’s human resources for technical and economic development.
Evolutionary biologists are keenly aware of the need for increased education in and understanding of science. The subject matter of evolutionary biology includes topics that directly impinge on individuals’ health and welfare, such as inherited disease, gene therapy, infectious disease, and the evolution of antibiotic resistance by pathogens, food production, agricultural pest management, genetic engineering, bioremediation, conservation, and the effects of global warming. Issues related to evolution, such as genetic differences among human populations, the fossil history of life, and indeed, the reality of evolution itself, are frequent topics of public discourse. Yet much of the public does not understand basic genetics or evolutionary biology. Incredible as it may seem in an age of spacecraft and supercomputers, polls find that more than half of the American public does not even believe in the scientific veracity of evolution, the unifying principle of all of biology.
Although some professional biologists have devoted great efforts to educating the public, the greatest efforts in public outreach in the United States have been made by organizations such as the National Center for Science Education, and the largest educational role has been played by secondary school teachers. Professional biologists should devote more effort to public education, availing themselves of opportunities such as press releases, engagement with the media, and museum exhibits. They should take every opportunity to point out the evolutionary dimensions of biological phenomena that capture the public’s attention; for instance, pests and disease organisms do not merely "mutate" or "develop" resistance to drugs—they evolve resistance. Heightened efforts to teach about evolution and related subjects are also required at both the college and secondary levels.
CONCLUSION
Researchers in molecular and developmental biology, physiology, ecology, animal behavior, psychology, anthropology, and other disciplines continue to adopt the methods, principles, and concepts of evolutionary biology as a framework. Likewise, applied research in forestry, agriculture, fisheries, human genetics, medicine, and other areas has increasingly attracted scientists trained in evolutionary biology. Evolutionary biologists have expanded their vision, addressing both basic questions throughout the biological disciplines and problems posed by society's needs. As a result of both the rapid growth of this "evolutionary work force" and technological advances in areas such as molecular methodology, computing, and information processing, progress in evolutionary biology and related areas is more rapid now than ever before. With the appropriate and necessary support in education and research, the evolutionary disciplines will make ever greater contributions to applied and basic knowledge.
Evolutionary biology plays a central role in the complexity of biological systems. Evolution is the source of biocomplexity. The continued and enhanced support of this field is critical to maximizing the nation’s research progress in both basic and applied arenas. In terms of societal needs for the twenty-first century, the time to make the investment in evolutionary biology is now, while there is still time either to change current trends or to better prepare us to deal with their consequences. Current and projected population levels will result in increasing environmental impacts, increasing pressure on food production, ever greater challenges to biological diversity, and enhanced opportunities for the emergence of new diseases. A healthy scientific base in evolutionary biology is an essential element in preparing us to meet these issues. Evolutionary biology must be at the heart of the nation’s research agenda in biology, just as it is at the heart of the field of biology.
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