Opportunities in Biology (1989) / Chapter Skim
Currently Skimming:
8. Evolution and Diversity
8. Evolution and Diversity
Pages 260-286
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 260... ...
In recent years, new techniques and approaches have opened exciting new avenues of investigation of the processes that generate evolution and diversity. As a result, greater opportunities exist now for advancing knowledge than during any period since the 1930s and 1940s, when evolutionary biology and genetics became united in what came to be called the modern synthesis of evolutionary biology.
|
From page 261... ...
A similar situation accounts for the repeated evolution of antibiotic resistance in bacteria: Rare bacterial types containing genes for resistance are favored in the presence of the antibiotic and eventually displace the normal sensitive types. In this case, the overuse of inexpensive antibiotics, not only in medicine but in animal feed, fish culture, and agriculture, has promoted the evolution of antibiotic resistance in a wide spectrum of microorganisms.
|
From page 262... ...
~ ~ I :~ ~ ~ ~ ~ :u~n~de~rstand ~ these apparent paradox.: : Many ~::oT: tog :~InsectIciae r~s~stances :: ~ ~ ~ ~ ~ ~ ~ ~ ~ :: ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ :~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~re~s~u~tt::~from::~si~ngle~ m~:utant~ :9~en~es~ :~:: Th~Q:~ resistance genes am often~part~'al~y~ :: ~ Dominant, ~so~:~the~change ~in:~th~e ~frequen~of the ~resistance~:g~ne~is~go~rern~ed: ~ ::; : : ~: ~ : LO : V_ : I~ ~ ~ .
|
From page 263... ...
And they have made possible an integration of the techniques of molecular biology with questions of field natural history, such as in the use of mitochondrial DNA polymorphisms to study population structure and migration in fish and other organisms. Application of the techniques of molecular biology has made possible, for the first time, the beginnings of a synthesis of microbiology and evolutionary biology.
|
From page 264... ...
Whether DNA sequences actually evolve with regular rates like molecular clocks is still much debated, but the data so far suggest at least moderate regularity. The concept of the molecular clock has provided a unique and powerful time dimension in evolutionary studies and has augmented as well as complemented inferences from the fossil record.
|
From page 265... ...
And the processes of speciation and extinction, while fundamental to evolution and diversity, are population, not molecular, processes. THE EVOLUTIONARY PROCESS Population Genetics Continues to Emphasize Genetic Variation Its Nature, Causes, and Maintenance in Populations Studies of population genetics or genetic variation have become significantly more sophisticated with the use of molecular techniques and new types of material, including microbial organisms and chloroplast and mitochondrial DNA.
|
From page 266... ...
~ levels has been a central issue: In population genet'¢s~tor more than a I :: d~e~d~e:~but it: has Edified ~resolOtion~:~b~ause:: most statistical tQStS of:: ob-: I ~ :: ~ ~1 : i: sewed gene::::frequ~e~ncies~::and:~:~:mos t labbrdtory~exper:iments :lack ~su~ff~ient :~:::po~r to :detect~:selection:~co~f:icie:nts of~:t~he: relevant :magn~itude~. ~ ~AIt~hbug:h: :~:most random :amino:acid substitutions might be:~expected~to ~ harmful kinky::: ::~a :small proportion of harmful mutations~ever become: established ~as~pply ~:morphi:sms In Natal: ,mpu~l~at~ns.~ A ~:sig~nifica~nt proportion~of alleles that :~bemme ~Iy~morphic~ might therefore be expected to :be s~elebti~vely:~or nearly::: :: :~: :~:Th~e idea~:~behin:d~ the: study of: DNA sequencers is:~:t:h:at~:nucleotide poly-: morphisms bt~:~si~lent~sitas, which do not change amino acid sequences, can ~DQ :useo ashy internal standards for comparison wan amino acid ~:lymori: ~ ~p~h:ism~s in :the same gene.
|
From page 267... ...
Recombination, traditionally viewed as important from the standpoint of creating genetic variation through new combinations of genes, has taken on a new dimension in population genetics because of its conservative role in maintaining similarity between members of multigene families. However, little is known about the rate of gene conversion in multigene families or about the role of intragenic recombination in creating new genetic variation.
|
From page 268... ...
Three approaches are taken in these investigations: field, experimental, and theoretical. Significant advances have come from the analysis of the genetic variation and structure in natural populations.
|
From page 269... ...
The study of speciation, one of the most important fields of research in evolutionary biology, has a direct bearing on our understanding of the origin of organismal diversity in the past, the present, and the future. It has left the descriptive, comparative phase that predominated in the past for a more empirical approach to the study of speciation mechanisms.
|
From page 270... ...
For example, plants under stress manifest marked phenotypic changes that are associated with heritable changes in copy number of several multigene families including ribosomal DNA sequences. New methods of manipulating and cloning large DNA molecules will be critical to the study of evolution at the level of the chromosome.
|
From page 271... ...
Indeed, some workers have begun to examine individual variation in physiological traits and to apportion the variation into genetic and nongenetic causes in attempts to determine physiological mechanisms. Important Advances Have Been Made in Behavioral Ecology and Evolutionary Biology The understanding of such phenomena as habitat use, food selection, social aggregation, cooperation, cannibalism, and ritualized conflict has greatly in
|
From page 272... ...
Although modern molecular techniques promise to contribute to an understanding of numerous unresolved questions related to the processes and history of evolution, equally important contributions will emerge from new conceptual, statistical, and technical approaches in areas such as population genetics, phylogenetic analysis, and developmental biology. Foremost among the poorly understood areas in evolution are the relations between evolutionary processes at the population level and the longer term evolutionary changes involved in the origin of species and higher taxa.
|
From page 273... ...
The greatest progress will come when the mechanisms of development are more fully understood. Even now we can hope for some understanding, perhaps by developmental comparisons and experiments not only between distantly related kinds of organisms such as frogs and salamanders, but also between closely related species in which hybridization or experimental transfer of genetic material may prove feasible.
|
From page 274... ...
Systernatics Is a Key Discipline in Evolutionary Biology In a Chinese proverb, calling things by their proper names systematics-is the beginning of wisdom. Modern systematics, which is basic to the study of adaptation, stresses the basic recognition and naming role, but simultaneously reaches out to all other disciplines concerned with biological diversity.
|
From page 275... ...
275 EVOLlJTION AND DIVERSITY ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ 1 FUNCTIONAL MQRPHOI~) GY AND ~EVOI1ITIObIARY E=LOGY G t L k Victoria Tanganyika and Malawi-are 1=~ ; ~ ~ ~ In general, when species coexist they are ~riltioning some resource Hi: ;~from~the leaves of higher plants Some ~eat;whol~e fish Some eat~nvette Their aws show rG G Kabul HO y in shape :sec a brates, and so on.
|
From page 276... ...
Two stand out in the sense that progress toward their solutions is needed to put the other disciplines on a permanently sound basis. The first problem is to define the magnitude and causes of biological diversity, and the second is to determine the most reliable measures of homology and their implications for phylogenetic relationships.
|
From page 277... ...
Thus, the study of biological diversity and the desire for its preservation are not based on esthetic principles alone. Systematics Also Includes Studies of the Interrelationships Among Organisms Studies on phylogenetic relationships.among organisms aid in the development and evaluation of theories about evolutionary processes.
|
From page 278... ...
One of the chief tasks of systematics is the elucidation of phylogenetic, or genealogical, relationships among organisms. Inference of genealogy is a desirable goal both for fossilized forms and for living organisms whose ancestry is poorly documented in the fossil record.
|
From page 279... ...
Electrophoretically distinguishable proteins are now routinely used to distinguish species and to estimate phylogenetic relationships among closely related species, and restriction enzyme digests of DNA sequences such as mitochondrial DNA provide numerous systematic characters. EVOLUTIONARY HISTORY The Fossil Record Makes Special Contributions to Evolutionary Biology and to Knowledge of Preseni-Day Diversity Although questions of both process and result are central in evolution and diversity, the history of evolution has only one source of primary direct evidence, one court of last resort, which is the fossil record.
|
From page 280... ...
280 OPPORTUNITIES IN BIOLOGY ~ ~ ~ ~ ~ ~ ~ ~ THE RISE OF THE WANTS ~ ~ ~ I :~ ~ ~ :: n Unit:;: ~ ~ar\Jarc ~:~:unl Grsr :y rece:lven:t 1Q t~l:rst~ tnown::soecl:m~ens~:::ot fossil ~ ~ ~ ~ ~ ~ ~ ~ :: ~ ~ Ants of;~Mesozo~ic Age, Ohio Beautifully preserYQd~spQcime~n~s~;~ in the clear :: : : : : ~ : ::: : : :: : :: : : ~1~ ~ orange amber from a ~r~dwodd ~tree~th~at~grew~80 ~m~ill~n~years ~ ago in News Jersey. Use speci~mens~we~re~som~ing of a breakthrough in the~study~ of 1 insect ~evolution.
|
From page 281... ...
Although the background rate of extinction is low-estimated as about one global extinction per million species per year-extinction is not only frequent on a geological time scale but has been responsible for many complete turnovers in the biological composition of the earth. A proper understanding of the evolutionary process is impossible without knowledge of rates of extinction, quite apart from the importance of such knowledge in evaluating the magnitude of the increase in rates of extinction resulting from human activities in modern times.
|
From page 282... ...
Until about 1.7 billion years ago, well after the origin of living systems, the atmosphere contained too little oxygen to sustain obligately airbreathing forms of life. Day length has progressively lengthened as the distance between the earth and moon has gradually increased, and there is good evidence that the earth's average surface temperature has changed markedly.
|
From page 283... ...
Other events, such as the advent of photosynthesis, oxygen-dependent respiration, the anaerobic-aerobic global ecosystem, nucleated cells, and eukaryotic sexual reproduction, have been addressed only recently with the upsurge of interest in the Precambrian fossil record. Future studies will promote a better understanding of the timing and context of major evolutionary events in the history of life on earth.
|
From page 284... ...
Museums, the traditional home of systematics, will find it necessary to expand their facilities and personnel to encompass statistical, molecular, and experimental approaches. The traditionally modest sums granted to systematists will not support molecular investigations, and it will be useful to set up facilities for molecular systematics that can be used by multiple workers.
|
From page 285... ...
Research questions change continually, and it is important that museum collections remain an effective source of empirical data and that the data be actively studied and described by competent specialists. The paleontological collections of the United States are in reasonably good shape, thanks to many years of financial support from the Biological Research Resources program of the National Science Foundation.
|
From page 286... ...
Finally, what little effort is expended to protect plants is almost entirely devoted to crop plants and their wild relatives about 150 species out of the more than 260,000 kinds of plants known. Botanists estimate that tens of thousands of kinds of plants could probably be developed into useful crops~ot only for food but also as sources of medicines, oils, waxes, and other chemicals of industrial importance-if we would carry out the appropriate investigations, identify them, and develop them according to their cultural requirements.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.