Michael Bettinger, Jr born on Feb 28, - died on Apr 19, at the age of Toggle navigation. Mobile Apps Login. Full Profile. Mentions about a name: Michael Bettinger. Lived in:. House of Representatives, Senate of PA. Work Company:. West Chester University of Pennsylvania - Dabakan Fine Art Owner. Professionals Engineers Engineering Specialist. Motor Vehicle Operator. Passenger Driver. Health Practitioner. Chief Executive. Community Service Manager. Operations Manager.
Date of birth:. Publications Michael Bettinger - Writer. Publishing: Publication:. Related Names Bettinger Bettinger. Login to view premium data. Rodney J. Lovenheim, Anderson, Drew M. Dynarski, Susan M. Scott-Clayton, The effects of student loans and need-based grants in China's higher education ," China Economic Review , Elsevier, vol. Elsayed, Mahmoud A. Carruthers, Celeste K.
Pell grants and college choices ," Journal of Public Economics , Elsevier, vol. Alex Solis, Solis, Alex, Susan Dynarski, Dynarski, Susan, Blom, Andrew Barr, Ehrenberg, R. Clotfelter, Charles T. Michael F. Owens, Lovenheim, Michael F. Hickman, Daniel C. Student aid design and socioeconomic achievement disparities in higher education ," Labour Economics , Elsevier, vol.
Charles T. Ladd, Fox, Bruce, Donald J. The impact of lottery scholarships on enrollment in Tennessee ," Journal of Urban Economics , Elsevier, vol. Cited by: Fredrick M. Wamalwa, Fredrick M. Fredrick M. Mark J. World Bank, David K. Dante Contreras, Contreras, Dante, Abhijit V. Gregory L. Haugan, Eric V. Edmonds, Eric V. Strauss ed. Bergman, Mats A. Card ed. John A. Masi, Barbara, Richard M. Zolt, Jere R.
Emanuela di Gropello, Orazem, Peter F. Noussair, Kasper Brandt, Ravallion, Martin, Rajeev Dehejia, Hammer, Ravikumar, Kremer, Michael R. Joshua D. Dammert,Ana C. Dammert, Ana C. Grant Miller, Marco Manacorda, Manacorda, Marco, Manuel Denzer, Lant Pritchett, MacLeod, Bentley, Ryan, Michela Ponzo, Jackson, C. Kirabo, Song, Yang, Kennedy, Kendall, Kendall J.
Kennedy, Singleton, John, John D. Singleton, Murat G. Alejandro J. Eskeland,Gunnar S. Benjamin A. Olken, Bhavnani, Isaac M. Mbiti, Glewwe, Paul, Glick, Peter, Colm Harmon, Nunley, John M. Andrews, Donald W. Donald W. Baum, Donald R. Zau, Uwaifo Oyelere, Ruth, Francisco A. Gallego, Lamarche, Carlos, Charles Kenny, Fryer, Jr, Paul Glewwe, Hungerman, Daniel M. How large-scale subsidy programs affect private-school revenue, enrollment, and prices ," Journal of Public Economics , Elsevier, vol.
Daniel M. Bird, Richard M. William Easterly, Florencia Torche, Zhang, Hongliang, Heinrich, Carolyn J. Christoph Eder, Dustan, Andrew, Eric A. Hanushek, Mohamad Fahmi, Alan B. Krueger, Alan B. Rodrik, Dani, Carrillo, Bladimir, Bladimir Carrillo, Vira Semenova, Estevan, Fernanda, Christiansen Arndt, Argentino Pessoa, Esther Duflo, Naveen Kumar, Larry Willmore, Michael Kremer, Susanne Link, Lant Pritchett, Justin Sandefur, Murathi Kiratu, Nixon, Justin C.
Andrew E. Cacault, M. Vazquez, Jacqmin, Julien, Tenaa, Wright, Nicholas A. Matsuda, Kazushige, Evans, Cited by: Steven W. Dynarski, Reber, See citations under working paper version above. Cited by: Seemanti Ghosh, Wei Chen, Cited by: Celeste K. Cited by: Colin Gray, Darolia, Rajeev, The effect of federal financial aid availability on postsecondary enrollment ," Journal of Public Economics , Elsevier, vol. Frauke H. Ran I. York, Elizabeth W. Hastings, Justine S. Justine S.
Zimmerman, Castleman, Benjamin L. Katharine G. Abraham, Katharine G. Brent J. Isphording, Brian J. Skimmyhorn, Lisa J. Stefanie P. Seemanti Ghosh, Barrios-Fernandez, Andres, De Walque,Damien B. James J. Heckman, James J. Timothy J. Sylvain Chareyron, Drew M. Narayan, Ayushi, Brian G. Schiff, Graves, Jennifer. Sarah R. Goodman, Peter, Frauke H. Universidad de Montevideo..
Martin F. Timothy N. Bond, Timothy N. Joshua Hyman, Bleemer, Zachary, Joshua S. Smith Jonathan, Naihobe Gonzalez, "undated". Nicholas W. Lucia Rizzica, Johannes S. Staub, Kunz, Johannes S. Mette T. Damgaard, Experimental evidence on the benefits of college matriculation support from high schools versus colleges ," Economics of Education Review , Elsevier, vol.
Joseph G. Raj Chetty, Evidence from administrative data ," Economics of Education Review , Elsevier, vol. Benjamin N. Swensen, Lindo, Jason M. Madrian, Brigitte, Brigitte C. Dayanand S. Marx, Benjamin M. Effects of information on student loan take-up ," Economics of Education Review , Elsevier, vol. Sean P. Amanda Pallais, Melissa Whatley, Page, Alexis Le Chapelain, Benjamin W.
Castleman, Jeremy McCauley, Meyer, Andrew G. Joselynn Hawkins Fountain, Sandra McNally, Bridget Terry Long, Barr, Andrew, Burgess, Simon, S ," Journal of Public Economics , Elsevier, vol. Brian P. Sorensen, Michael S. Kofoed, Tavares, Priscilla Albuquerque, Phillip B. Russell, Soter, Philippis, Marta De, Marta De Philippis, Lapid, Patrick Andrew, Daniel C. Meyer, Papageorge, Cassandra M. Dills, Angela K. Hilmer, Christiana E. Cheslock, John J. The effects of tenure-track and part-time faculty on student achievement ," China Economic Review , Elsevier, vol.
Siegfried, Saavedra, Gabriel Heller Sahlgren, Drichoutis, Oksana Tokarchuk, Schmitz, Andrew Meyer, Hoppe, Eva I. Eva I. Kusterer, Mohammad Noori, Li, Musau, Andrew, Simons, Andrew M. Paloyo, Alfredo R. Pickering, Lee, Possebom, Vitor, Gallen, School of Economics and Political Science. Andreas Ostermaier, Naveen Sunder, Small, Temple, Jonathan R. Mahmoud A.
Elsayed, Starr, Wooldridge, Wooldridge, Jeffrey M. Imbens, Guido W. Guido M. Guido W. Behrman, Jere R. Dang,Hai-Anh H. Hai-Anh H. Glewwe, Miller, Luke C. Al-Hasan,
Her paper is available from Claudia Landwehr upon request. Jeannette Brosig-Koch from the University of Duisburg-Essen has been invited to give a talk on "Physician performance pay: Evidence from a laboratory experiment" at the faculty seminar, - pm. Before starting her current position as Professor at the University of Duisburg-Essen in , she worked as Professor at the University of Cologne and as Assistant Professor at the University of Magdeburg. After the talk, there will be the opportunity for informal exchange over lunch.
Please register with Simone Ndongala ndongala politik. He holds a Dr. The topic of the talk will be " How homogeneous is the FDI-growth relationship? A cluster estimation approach to parameter heterogeneity. His work has been published, inter alia, in Econometric Theory and the Journal of the American Statistical Association. Gerald Eisenkopf will give a two day workshop on experimental research methods in Mainz. The course is primarily for doctoral and post-doctoral students and will cover the topics of programming with zTree, experimental implementation and hints on how to deal with experiment participants.
The deadline for registration for the course is the Please register by sending a mail with your name and affiliation to ipp-mainz uni-mainz. He will talk about problems of simultaneous statistical inference. An overview of multiple statistical decision problems, classical as well as recent solutions which account for the intrinsic dependencies and the amount of signals in the data will be presented.
Special attention is given to multiple testing and control of the false discovery rate. He wrote: "Why should you care about this workshop? Well, your career depends on your ability to communicate or lack of it. Technical knowledge is necessary but not sufficient. So, you need these skills and the confidence that goes with having them. Why listen to me? I will be available for several days, so make use of me. Find more information here: Content of the Workshop , Preparation for the Workshop.
Daniel Schunk to give a talk at the faculty seminar, - pm. The topic is "Choice and personal responsibility: What is a morally relevant choice? Hans van Kippersluis from the Erasmus University Rotterdam has been invited by Professor Reyn Van Ewijk to give a talk at the faculty seminar, - pm. The talk takes place in room "Dekanatssaal" ReWi I building, Martin Leroch to give a talk on "Towards modeling and simulating changes in societies". Time slots will be available for individual meetings and conversations with Prof.
Florian Rupp after the lecture. Keynote speaker is Prof. Ron Davies from the University College Dublin. More information and a workshop schedule are available here. The talk will be from 6 - 7. Gallen in His research is interdisciplinary and crosses the boundaries of economics to social psychology, finance, political science, criminology, and biology. He uses field and lab experimental methods, and his current research projects cover topics like honesty, employee motivation, business culture and unethical behavior, as well as context-dependence in economic preferences.
Daniel Schunk at the University of Mainz host an international research conference in Economics of Education. The workshop is embedded in a summer school with international participants, taking place from 22 to 24 September. August 25th Press Release - Elementary School E-Learning Project How does the use of e-learning technologies influence the performance and motivation of elementary school students?
Florian Zimmermann from the University of Zurich has been invited by Professor Daniel Schunk to give a talk at the faculty seminar. Thereafter he started his current position as postdoctoral researcher at the University of Zurich. His active research focus connects the fields of behavioral economics, experimental economics and applied microeconomics.
Claudia Landwehr Prof. Philipp Harm will hold a presentation and discussion on the recent book by Thomas Piketty. Further information. Stefan Irnich invited Claudia Archetti from the University of Brescia to give a talk at the faculty seminar. The topic will be announced soon. In she obtained the tenure as associate professor in Operations Research. Claudia Archettis research activities focused on supply chain management and routing problems.
The workshop will be directed by Nidia Palacios. Nidia is an Italian-Argentinian Mezzoso-prano, who has successfully performed all over the world including, Paris, St. She will show how to use the voice, how to fill a stage, how to capture an audience and make them believe.
She has done so hundreds of times. From , he worked as a researcher at the MPIfG and was awarded his habilitation by the University of Heidelberg in The topic of the lecture is "A behavioral approach to the theory of the firm". An Experimental Investigation. Since he was first a lecturer and now an associated professor at the Department of Economics and Finance of the University of Canterbury. During this period he also was visiting professor at the University of Economics in Bratislava.
Since he works as member of the editorial of the Journal of Behavioral and Experimental Economics. Professor Servatkas research focuses are experimental economics, behavioral economics und social psychology. With his interdisciplinary approaches and his experience in building up an experimental laboratory he will enrich the IPP-community. The main purpose of this retreat was the exchange of research ideas between the different members of IPP.
Several research presentations on topics ranging from neurobiology to international economics and political science as well as many engaging discussions on how to proceed in the research cooperations took place. The workshop intends to provide a platform for the discussion of new ideas in the structural evaluation of labour market policies.
Particular attention will be given to modeling labour market policies in presence of search-and-matching frictions and information asymmetries. Submission of theoretical and empirical papers is equally encouraged. Keynote speech of the workshop will be delivered by Prof. Pierre Cahuc Ecole Polytechnique, Paris. Further information can be found here:.
He writes: "Why should you care about this workshop? Please register by September 19th by email to: ipp-mainz uni-mainz. Find more information here. One aim of the symposium is to discuss the policy implications of current research in auditing. Gronewold University of Potsdam , Prof. A young scholar workshop precedes the symposium. The symposium takes place at Potsdam on June Further information is available at:. Philipp Harms International Economics and Prof.
The workshop aims at stimulating the exchange of ideas in the fields of trade and open-economy macroeconomics. The keynote speech will be delivered by Fabio Ghironi University of Washington. Following a short presentation of goals and a roadmap of the IPP for the next years, the speaker, Prof. Daniel Schunk, the deputy speaker Prof.
After the elections, Prof. The talk was followed by a lively discussion and the group interacted for another hour in an informal get-together. In the evening, Prof. Fehr was awarded the Gutenberg Research Award. The main purpose of this retreat was an exchange of research ideas between the different members of IPP.
Upcoming Events. Location of the talk: Room GFG building. The workshop is open to everyone. Challenges for Agent-Based Modelling" - pm. January 28th Research Seminar with Roberto V. Gallen Martin Brown , from the University of St. January 21st Faculty Seminar with Sebastian Krautheim from the University of Passau Sebastian Krautheim , from the University of Passau has been invited to give a talk at the faculty seminar, - pm.
December 3rd Faculty Seminar with Michael Kosfeld from the Goethe - University Frankfurt Michael Kosfeld , from the Goethe - University Frankfurt has been invited to give a talk at the faculty seminar, - pm. Fischer, from the Swiss National Bank has been invited to give a talk on "The effect of self-financed property buyers on local house prices" at the faculty seminar, - pm. October 29th Faculty Seminar with Herbert Dawid from the University of Bielefeld Herbert Dawid , from the University of Bielefeld has been invited to give a talk at the faculty seminar, - pm.
June 11th Faculty Seminar with Charles Bellemare from the University of Laval Charles Bellemare from the University of Laval Canada has been invited to give a talk on " Life-cycle decisions, dynamic programming, and correlation neglect: experimental analysis of alternative decision rules " at the faculty seminar, - pm.
The preliminary dates for the course are: - Monday, 11th from 10 - Abstract: Virtual assistants, such as Amazon's Alexa or Apple's Siri, are quickly becoming features of everyday life, but little is known about their political responses. Michael Bettinger born on - died on at the age of Michael Bettinger born on Sep 29, - died on Mar 2, at the age of Michael Bettinger, Jr born on Feb 28, - died on Apr 19, at the age of Toggle navigation.
Mobile Apps Login. Full Profile. Mentions about a name: Michael Bettinger. Lived in:. House of Representatives, Senate of PA. Work Company:. West Chester University of Pennsylvania - Dabakan Fine Art Owner. Professionals Engineers Engineering Specialist.
Motor Vehicle Operator. Passenger Driver. Health Practitioner. Chief Executive. Community Service Manager. Operations Manager. Date of birth:. Publications Michael Bettinger - Writer. Publishing: Publication:.
Medical data and overall survival OS were assessed. A Cox regression model was performed to create an alternative prediction model, which includes significant prognostic factors. Results: Age, bilirubin, albumin and creatinine were the most important prognostic factors. The FIPS score was able to identify high-risk patients with a significantly reduced prognosis of a median survival of 5. These results were confirmed in the validation set median survival of 3.
Conclusions: The FIPS score is superior to established scoring systems for identifying high-risk patients with a reduced prognosis in patients with elective TIPS implantation. Keywords: Child-Pugh score; MELD score; liver cirrhosis; prognosis; risk stratification; transjugular intrahepatic portosystemic shunt. Michael Bettinger born on Sep 29, - died on Mar 2, at the age of Michael Bettinger, Jr born on Feb 28, - died on Apr 19, at the age of Toggle navigation.
Mobile Apps Login. Full Profile. Mentions about a name: Michael Bettinger. Lived in:. House of Representatives, Senate of PA. Work Company:. West Chester University of Pennsylvania - Dabakan Fine Art Owner. Professionals Engineers Engineering Specialist.
Motor Vehicle Operator. Passenger Driver. Health Practitioner. Chief Executive. Community Service Manager. Operations Manager. Date of birth:. Publications Michael Bettinger - Writer. Publishing: Publication:. Related Names Bettinger Bettinger.
This occurs because organisms become resistant to the pesticide through directional selection. Resistance of the housefly, Musca domestica, to DDT was first reported in Resistance to one or more pesticides has now been recorded in more than species of insects. Sustained directional selection leads to major changes in morphology and ways of life over geologic time. Evolutionary changes that persist in a more-or-less continuous fashion over long periods of time are known as evolutionary trends.
Directional evolutionary changes increased the cranial capacity of the human lineage from Australopithecus afarensis, human ancestors who lived four million years ago, with a small brain weighing somewhat less than one pound, to Homo sapiens, modern humans with a brain three and a half times as large. The more-or-less gradual increase in size during the evolution of the horse family from 50 million years ago to modern times is another of the many well studied examples of directional selection.
Two or more divergent traits in an environment may be favored simultaneously, which is called diversifying selection. No natural environment is homogeneous; rather, the environment of any plant or animal population is a mosaic consisting of more-or-less dissimilar subenvironments. There is heterogeneity with respect to climate, food resources, and living space.
Also, the heterogeneity may be temporal, with change occurring over time, as well as spatial, with dissimilarity found in different areas. Species cope with environmental heterogeneity in diverse ways. One strategy is the selection of a generalist genotype that is well adapted to all of the subenvironments encountered by the species. Another strategy is genetic polymorphism, the selection of a diversified gene pool that yields different genetic makeups, each adapted to a specific subenvironment.
One important factor in reproduction is mutual attraction between the sexes. The males and females of many animal species are fairly similar in size and shape except for the sexual organs and secondary sexual characteristics such as the mammary glands of female mammals. There are, however, species in which the sexes exhibit striking dimorphism.
Particularly in birds and mammals, the males are often larger and stronger, more brightly colored, or endowed with conspicuous adornments. But bright colors make animals more visible to predators; for example, the long plumage of peacocks and birds of paradise and the enormous antlers of aged male deer are cumbersome loads at best. Darwin knew that natural selection could not be expected to favor the evolution of disadvantageous traits, and he was able to offer a solution to this problem.
He proposed that such traits arise by sexual selection, which depends not on a struggle for existence in relation to other organic beings or to external conditions, but on a struggle between the individuals of one sex, generally the males, for the possession of the other sex.
Thus, the colored plumage of the males in some bird species makes them more attractive to their females, which more than compensates for their increased visibility to potential predators. Sexual selection is a topic of intensive research at present. The apparent altruistic behavior of many animals is, like some manifestations of sexual selection, a trait that at first seems incompatible with the theory of natural selection.
Altruism is a form of behavior that benefits other individuals at the expense of the one that performs the action; the fitness of the altruist is diminished by its behavior, whereas individuals that act selfishly benefit from it at no cost to themselves.
Accordingly, it might be expected that natural selection would foster the development of selfish behavior and eliminate altruism. This conclusion is not so compelling when it is noticed that the beneficiaries of altruistic behavior are usually relatives. They all carry the same genes, including the genes that promote altruistic behavior. Altruism may evolve by kin selection, which is simply a type of natural selection in which relatives are taken into consideration when evaluating an individuals fitness.
Kin selection is explained as follows. Natural selection favors genes that increase the reproductive success of their carriers, but it is not necessary that all individuals with a given genetic makeup have higher reproductive success. It suffices that carriers of the genotype reproduce more successfully on average than those possessing alternative genotypes.
A parent shares half its genes with each progeny, so a gene that promotes parental altruism is favored by selection if the behaviors cost to the parent is less than half its average benefits to the progeny. Such a gene will be more likely to increase in frequency through the generations than an alternative gene that does not promote parental care. The parent spends some energy caring for the progeny because it increases the reproductive success of the parents genes.
But kin selection extends beyond the relationship between parents and their offspring. It facilitates the development of altruistic behavior when the energy invested, or the risk incurred, by an individual is compensated in excess by the benefits ensuing to relatives.
In many species of primates as well as in other animals , altruism also occurs among unrelated individuals when the behavior is reciprocal and the altruists costs are smaller than the benefits to the recipient. This reciprocal altruism is found, for example, in the mutual grooming of chimpanzees as they clean each other of lice and other pests. Another example appears in flocks of birds that post sentinels to warn of danger. One crow sitting in a tree watching for predators, while the rest of the flock forages, incurs a small loss by not feeding, but this is well compensated by the protection it receives when it itself forages and others of the flock stand guard.
Darwin sought to explain the splendid diversity of the living world: thousands of organisms of the most diverse kinds, from lowly worms to spectacular birds of paradise, from yeasts and molds to oaks and orchids. His Origin of Species is a sustained argument showing that the diversity of organisms and their characteristics can be explained as the result of natural processes.
As Darwin noted, different species may come about as the result of gradual adaptation to environments that are continuously changing in time and differ from place to place. Natural selection favors different characteristics in different situations.
In everyday experience we identify different kinds of organisms by their appearance. Everyone knows that people belong to the human species and are different from cats and dogs, which in turn are different from each other. There are differences among people, as well as among cats and dogs; but individuals of the same species are considerably more similar among themselves than they are to individuals of other species.
But there is more to it than that: a bulldog, a terrier, and a golden retriever are very different in appearance, but they are all dogs because they can interbreed. People can also interbreed with one another, and so can cats, but people cannot interbreed with dogs or cats, nor these with each other. It is,. This is expressed in the following definition: species are groups of interbreeding natural populations that are reproductively isolated from other such groups.
The ability to interbreed is of great evolutionary importance, because it determines that species are independent evolutionary units. Genetic changes originate in single individuals; they can spread by natural selection to all members of the species but not to individuals of other species. Thus, individuals of a species share a common gene pool that is not shared by individuals of other species, because they are reproductively isolated. Although the criterion for deciding whether individuals belong to the same species is clear, there may be ambiguity in practice for two reasons.
One is lack of knowledge: it may not be known for certain whether individuals living in different sites below to the same species, because it is not known whether they can naturally interbreed. The other reason for ambiguity is rooted in the nature of evolution as a gradual process. Two geographically separate populations that at one time were members of the same species later may have diverged into two different species. Since the process is gradual, there is no particular point at which it is possible to say that the two populations have become two different species.
It is an interesting curiosity that some antievolutionists have referred to the existence of species intermediates as evidence against evolution; quite the contrary, such intermediates are precisely expected. A similar kind of ambiguity arises with respect to organisms living at different times. There is no way to test whether or not todays humans could interbreed with those who lived thousands of years ago. It seems reasonable that living people, or living cats, would be able to interbreed with people, or cats, exactly like those that lived a few generations earlier.
But what about the ancestors removed by one thousand or one million generations? The ancestors of modern humans that lived one million years ago about 50 thousand generations are classified in the species Homo erectus, whereas present-day humans are classified in a different species, Homo sapiens, because those ancestors were quite different from us in appearance and thus it seems reasonable to conclude that interbreeding could not have occurred with modern-like humans.
But there is no exact time at which Homo erectus became Homo sapiens. It would not be appropriate to classify remote human ancestors and modern humans in the same species just because the changes from one generation to the next are small. It is useful to distinguish between the two groups by means of different species names, just as it is useful to give different names to childhood, adolescence, and adulthood, even though there is no one moment at which an individual passes from one to the next.
Biologists distinguish species in organisms that lived at different times by means of a commonsense rule: if two organisms differ from each other about as much as two living individuals belonging to two different species differ today, they are classified into separate species and given different names.
Bacteria and blue-green algae do not reproduce sexually, but by fission. Organisms that lack sexual reproduction are classified into different species according to criteria such as external morphology, chemical and physiological properties, and genetic constitution.
The definition of species given above applies only to organisms able to interbreed. Since species are groups of populations reproductively isolated form one another, asking about the origin of a species is equivalent to asking how reproductive isolation arises between populations. Two theories have been advanced to answer this question.
One theory considers isolation as an accidental byproduct of genetic divergence. Populations that become genetically less and less alike as a consequence, for example, of adaptation to different environments may eventually be unable to interbreed because their gene pools are disharmonious. The other theory regards isolation as a product of natural selection.
Whenever hybrid individuals are less fit than nonhybrids, natural selection directly promotes the development of reproductive isolation. This occurs because genetic variants interfering with hybridization have greater fitness than those favoring hybridization, given that the latter are often present in poorly fit hybrids.
Scientists have shown that these two theories of the origin of reproductive isolation are not mutually exclusive. The geographic separation of populations derived from common ancestors may continue long enough that the populations become completely differentiated species before coming together again. As the separated populations continue evolving independently, morphological differences may arise. Examples of adaptive radiation are common in archipelagos far removed from the mainland.
The Galapagos Islands are about miles off the west coast of South America. When Darwin arrived there in , he discovered many species not found anywhere else in the world for example, 14 species of finch known as Darwins finches. These passerine birds have adapted to a diversity of habitats and diets, some feeding mostly on plants, others exclusively on insects. The various shapes of their bills are clearly adapted to probing, grasping, biting, or crushing the diverse ways in which these different Galapagos species obtain their food.
The explanation for such diversity which is not found in finches from the continental mainland is that the ancestor of Galapagos finches arrived in the islands before other kinds of birds and encountered an abundance of unoccupied ecological opportunities. The finches underwent adaptive radiation, evolving a variety of species with ways of life capable of exploiting niches that in continental faunas are exploited by different kinds of birds. Striking examples of adaptive radiation occur in the Hawaiian Islands.
The archipelago consists of several volcanic islands, ranging from less than one million to more than ten million years in age, far away from any continent or other large islands. An astounding number of plant and animal species of certain kinds exist in the islands while many other kinds are lacking. Among the species that have evolved in the islands, there are about two dozen about one-third of them now extinct of.
In fact, all but one of Hawaiis 71 native bird species are endemic; that is, they have evolved there and are found nowhere else. About one-fourth of the worlds total number of known species of Drosophila flies more than are native Hawaiian species. The species of Drosophila in Hawaii have diverged by adaptive radiation from one or a few colonizers, which encountered an assortment of ecological opportunities that in other lands are occupied by different groups of flies or insects.
Examples of rapid speciation are also known in many organisms. Instances of rapid speciation are sometimes called quantum or saltational speciation. An important form of quantum speciation occurs as a result of polyploidy, which is the multiplication of entire sets of chromosomes. This can happen in a single generation, for example, if meiosis fails so that an individuals gametes have two sets of chromosomes, rather than only one. If a male and a female gamete, each with two sets of chromosomes, combine, the resulting individual will have four sets, rather than two sets, of chromosomes.
A typical diploid organism carries in the nucleus of each cell two sets of chromosomes, one inherited from each parent; a polyploid organism has several sets of chromosomes. Many cultivated plants are polyploid: bananas have three sets of chromosomes, potatoes have four, bread wheat has six, some strawberries have eight. In animals, polyploidy is relatively rare because it disrupts the balance between chromosomes involved in the determination of sex.
But polyploid species are found in hermaphroditic animals individuals having both male and female organs , which include snails and earthworms, as well as in forms with parthenogenetic females which produce viable progeny without fertilization , such as some beetles, sow bugs, goldfish, and salamanders. It is possible to look at two sides of evolution: one, called anagenesis, refers to changes that occur within a lineage; the other, called cladogenesis, refers to the split of a lineage into two or more separate lineages.
Anagenetic evolution has, over the last four million years more than tripled the size of the human brain; in the lineage of the horse, it has reduced the number of toes from four to one. Cladogenetic evolution has produced the extraordinary diversity of the living world, with more than two million species of animals, plants, fungi, and microorganisms.
The evolution of all living organisms, or of a subset of them, can be represented as a tree, with branches that divide into two or more as time progresses. Such trees are called phylogenies. Their branches represent evolving lineages, some of which eventually die out while others have persisted to the present time.
Evolutionists are interested in the history of life and hence in the topology, or configuration, of evolutions trees. They also want to know the anagenetic changes along lineages and the timing of important events. Tree relationships are ascertained by means of several complementary sources of evidence. First, there is the fossil record, which provides definitive evidence of relationships among some groups of organisms, but is far from complete and often seriously deficient.
Second, there is comparative anatomy, the comparative study of living forms; and the related disciplines of comparative embryology, cytology, ethology, biogeography, and others. In recent years the comparative study of informational macromolecules proteins and nucleic acids has become a powerful tool for the study of evolutions history. We saw earlier how the results from these disciplines demonstrate that evolution has occurred.
Advanced methods have now been developed to reconstruct evolutions history. These methods make it possible to identify whether the correspondence of features in different organisms is due to inheritance from a common ancestor, which is called homology.
The forelimbs of humans, whales, dogs, and bats are homologous. The skeletons of these limbs are all constructed of bones arranged according to the same pattern because they derive from an ancestor with similarly arranged forelimbs Figure 1. Correspondence of features due to similarity of function but not related to common descent is termed analogy.
The wings of birds and of flies are analogous. Their wings are not modified versions of a structure present in a common ancestor but rather have developed independently as adaptations enabling them to fly. Homology can be recognized not only between different organisms but also between repetitive structures of the same organism. This has been called serial homology. There is serial homology, for example, between the arms and legs of humans, among the seven cervical vertebrae of mammals, and among the branches or leaves of a tree.
The jointed appendages of arthropods are elaborate examples of serial homology. Crayfish have 19 pairs of appendages, all built according to the same basic pattern but serving diverse functions sensing, chewing, food handling, walking, mating, egg carrying, and swimming. Serial homologies are not useful in reconstructing the phylogenetic relationships of organisms, but they are an important dimension of the evolutionary process.
Relationships in some sense akin to those between serial homologs exist at the molecular level between genes and proteins derived from ancestral gene duplications. The genes coding the various hemoglobin chains are an example. About million years ago a chromosome segment carrying the gene encoding hemoglobin became duplicated, so that the genes in the different segments thereafter evolved in somewhat different ways, one eventually giving rise to the modern gene coding for hemoglobin, the other for hemoglobin.
The hemoglobin gene became duplicated again about million years ago, giving rise to the fetal hemoglobin. The , , and hemoglobin genes are homologous: similarities in their DNA sequences occur because they are modified descendants of a single ancestral sequence. Morphological evolution is a more-or-less gradual process, as shown by the fossil record. Major evolutionary changes are usually due to a building up over the ages of relatively small changes.
But the fossil record is often discontinuous, so that it fails to manifest the gradual transition from one form to another. Fossil strata are separated by sharp boundaries; accumulation of fossils within a geologic deposit stratum is fairly constant over time, but the transition from one stratum to another may involve gaps of tens of thousands of years. Different species, characterized by small but discontinuous morphological changes, typically appear at the boundaries between strata, whereas the fossils within a stratum exhibit little morphological variation.
This is not to say that the transition from one stratum to another always involves sudden changes in morphology; on the contrary, fossil forms often persist virtually unchanged through several geologic strata, each representing millions of years. Paleontologists attributed the apparent morphological discontinuities in the fossil record to the discontinuity of the sediments; that is, to substantial time gaps encompassed in the boundaries between strata.
The assumption was that, if the fossil deposits were more continuous, they would show a more gradual transition of forms. Even so, morphological evolution would not always keep progressing gradually, because some forms, at least, remain unchanged for extremely long times. Examples are the lineages known as living fossils: the lamp shell Lingula, a genus of brachiopod that appears to have remained essentially unchanged since the Ordovician Period, some million years ago; or the tuatara Sphenodon punctatus , a reptile that has shown little morphological evolution for nearly million years since the early Mesozoic.
According to some paleontologists, however, the frequent discontinuities in the fossil record are not artifacts created by gaps in the record, but rather reflect the true nature of morphological evolution, which happens in sudden bursts associated with the formation of new species. The lack of morphological evolution, or stasis, of lineages such as Lingula and Sphenodon is in turn due to lack of speciation within those lineages. The proposition that morphological evolution is jerky, with most morphological change occurring during the brief speciation events and virtually no change during the subsequent existence of the species, is known as the punctuated equilibrium model of morphological evolution.
Most evolutionists, however, agree that evolution is on the whole gradual, rather than discontinuous. Molecular biology has made possible the comparative study of proteins and nucleic acid, DNA, which is the repository of hereditary and therefore, evolutionary information. The relationship of proteins to DNA is so immediate that they closely reflect the hereditary information.
This reflection is not perfect, because the genetic code is redundant and, consequently, some differences in DNA do not yield differences in the synthesized proteins. Nevertheless, proteins are so closely related to the information contained in the DNA that they, as well as the nucleic acids, are called informational macromolecules. Nucleic acids and proteins are linear molecules made up of sequences of units nucleotides in nucleic acids, amino acids in proteins which retain considerable amounts of evolutionary information.
Comparing two macromolecules establishes the number of their units that are different. Because evolution usually occurs by changing one unit at a time, the number of differences is an indication of the recentness of common ancestry. Changes in evolutionary rates may create difficulties, but macromolecular studies have two notable advantages over comparative anatomy and other classical disciplines.
One is that the information is more readily quantifiable. The number of units that are different is precisely established when the sequence of units is known for a given macromolecule in different organisms. The other advantage is that comparisons can be made even between very different sorts of organisms.
There is very little that comparative anatomy can say when organisms as diverse as yeasts, pine trees, and human beings are compared; but there are homologous DNA and protein molecules that can be compared among all three Figure 1. Informational macromolecules provide information not only about the topology of evolutionary history that is, the configuration of evolutionary trees , but also about the amount of genetic change that has occurred in any given branch.
It might seem at first that determining the number of changes in a branch would be impossible for proteins and nucleic acids, because it would require comparison of molecules from organisms that lived in the past with those from living organisms. But this determination can actually be made using elaborate methods developed by scientists who investigate the evolution of DNA and proteins. One conspicuous attribute of molecular evolution is that differences between homologous molecules can readily be quantified and expressed as, for example, proportions of nucleotides or amino acids that have changed.
Rates of evolutionary change can therefore be more precisely established with respect to DNA or proteins than with respect to morphological traits. Studies of molecular evolution rates have led to the proposition that macromolecules evolve as fairly accurate clocks. If the rate of evolution of a protein or gene were approximately the same in the evolutionary lineages leading to different species, proteins and DNA sequences would provide a molecular clock of evolution.
The sequences could then be used to reconstruct not. This tree is based on the amino acid sequences of a small protein, cytochrome c. Although the evolutionary relationships are not all accurate, it is remarkable that they can be determined by examining a single protein.
A more nearly correct evolutionary tree can be constructed by combining data for several proteins. The molecular evolutionary clock is not a metronomic clock, like a watch or other timepiece that measures time exactly, but a stochastic clock like that of radioactive decay. In a stochastic clock, the probability of a certain amount of change is constant, although some variation occurs in the actual amount of change. Over fairly long periods of time, a stochastic clock is quite accurate.
The enormous potential of the molecular evolutionary clock lies in the fact that each gene or protein is a separate clock. Each clock ticks at a different rate the rate of evolution characteristic of a particular gene or protein, but each of the thousands and thousands of genes or proteins provides an independent measure of the same evolutionary events. Evolutionists have found that the amount of variation observed in the evolution of DNA and proteins is greater than is expected from a stochastic clock; in other words, the clock is inaccurate.
The discrepancies in evolutionary rates along different lineages are not excessively large, however. It turns out that it is possible to time phylogenetic events with as much accuracy as may be desired; but more genes or proteins about two to four times as many must be examined than would be required if the clock were stochastically accurate. The average rates obtained for several DNA sequences or proteins taken together become a fairly precise clock, particularly when many species are investigated Figure 1.
The total number of differences for seven proteins cytochrome c, fibrinopeptides A and B, hemoglobins and , myoglobin, and insulin C-peptide were calculated for comparisons between pairs of species whose ancestors diverged at the time indicated. The solid line was drawn from the origin to the outermost point. The fit between the observed number of differences and the expected number as determined by the solid line is fairly good in general. However, in the primates points below the diagonal at lower left protein evolution seems to have occurred at a slower rate than in most other organisms.
Evolutionary theorizing has been controversial from its birth in the eighteenth century. No sooner had people like the Englishman Erasmus Darwin and the Frenchman Jean-Baptiste de Lamarck started putting forwards ideas of upward organic development, than the critics started to launch their counterattacks.
The greatest biologist of the age, George Cuvier , was a leader of the critique, arguing that evolution is a false, pernicious doctrine, religiously unacceptable, politically dangerous, and ideologically suspect. Things did not change during the nineteenth century.
Charles Darwin, the grandson of Erasmus, rightly known as the father of evolution, published his great work On the Origin of Species, in which he argued for the mechanism of natural selection, in Only a year later, Darwins great supporter Thomas Henry Huxley found himself debating the forces of reaction and status quo: first the comparative anatomist and paleontologist Richard Owen, and then publicly the Bishop of Oxford, Samuel Wilberforce Ruse b.
In the twentieth century, evolution continued to be controversial. Notoriously in in the state of Tennessee a school teacher, John Thomas Scopes, was prosecuted for teaching evolution, and although his conviction was overturned on appeal, it had a chilling effect on evolutionary ideas, particularly in schools Larson It was not indeed until the s and s that evolution started to find its way back into textbooks in the United States.
In the last part of the twentieth century, evolution certainly throve in universities and museums, but still it continued a source of much controversy. There was a court case in the state of Arkansas in , and then as the millennium drew to an end, more and more voices were raised against evolution. But even within the halls of evolutionism itself there was much controversy, with people like the Harvard entomologist and sociobiologist Edward O. Wilson on the one side arguing for an extension of evolutionary ideas to our own species, and his colleagues at Harvard the geneticist Richard Lewontin and the paleontologist Handbook of Evolution, Vol.
Stephen Jay Gould on the other side arguing that such extensions are scientifically unwarranted and morally dubious. In this brief overview I cannot hope to cover all the controversies that follow evolutionists at the beginning of a new century.
I therefore confine my discussion to some five controversies, hoping thereby to give the reader a good sense not only of the debates, but also of the excitement that surrounds one of the most important, if controversial, ideas of our time.
I start with a vigorous debate about the history of Darwinism itself. This is revealing not just for the past but also for our understanding of the present. Next, I move to some of the debate and discussions about origin-oflife studies. I then move to central issues to do with natural selection. This is followed by extensions to humankind. I conclude with the attacks from without, particularly by todays enthusiasts for so-called Intelligent Design. I begin with discussion of a controversy that is not so much about or within evolutionary theory itself, but rather about the history of evolutionism.
As was said at the beginning, evolutionary theory is a child of the eighteenth century Ruse a. It was then that discoveries of the fossil record and of strange organisms and the like started to persuade people to think that the Genesis-based account of origins is not correct Rudwick Rather, we must suppose that organisms came by a natural process of development from primitive forms. However, from the beginning, all would agree evolutionary theory was very much more than just a straight scientific theory.
They were enthusiasts of the chief secular philosophy or ideology of the age: progress. They believed that humans, unaided, can improve their knowledge, and through this their social conditions. Darwin and Lamarck and other early evolutionists took this ideology and read it into the biological world. Metaphorically, they saw evolutionary development as a progressive rise from the primitive to the complex, from the monad to the man, as they used to say.
Then generally, in good circular fashion, they read their biological progressivism back into culture, thinking that they had justified their overall ideology! Expectedly, the great critics of evolution notably Georges Cuvier in France and Adam Sedgwick in England opposed not only the factual basis of evolution, which to be frank was not very great, but also the ideological underpinnings.
Cuvier and Sedgwick and others were keen Protestants, and as such they saw progressivism striking directly at their central theological commitment to a Providential God: to a world where we humans can effect no lasting changes on our own but can seek salvation only by appealing to God for His mercy and his grace.
Evolutionary theory in those early days was therefore less a genuine scientific theory and more a kind of pseudoscience or secular religion. And this is the way. In the Origin of Species, published in , Darwin put forward a much firmer than hitherto understood empirical base for evolutionary change, appealing right across the spectrum of the biological world: instinct, paleontology, biogeography, anatomy, embryology, systematics, and more.
Thus he supported his belief in a gradual process of descent. Conversely, he used this belief in a gradual process of descent to illuminate problems in the various subdisciplines of the biological sciences. In short, it was Darwins hope that the Origin of Species would provide a new paradigm of research biology under the umbrella of evolution Ruse a. However, this was not to be. Darwins great supporters notably Thomas Henry Huxley had little interest in making a functioning professional science out of Darwinism.
They were not interested in evolutionary problems at an experimental level, being much more concerned with broad-scale issues to do with morphology and paleontology Desmond , And as all agree, for a long while after the Origin was published, evolutionary biology became not very Darwinian at all. Indeed, it owed far more to the transcendental idealistic morphology coming out of Germany, reaching back ultimately to the Naturphilosophen, than to anything to be found in the Origin of Species Richards ; Nyhart It is at this point that we start to enter into controversy.
I argue that what happened after the Origin was little more than a disaster from the point of view of science. Evolutionary biology was hijacked by others, notably Ernst Haeckel in Germany and Herbert Spencer and his followers in England and then in America. It remained as it has long been: a kind secular religion, an alternative to Christianity. As a science, it became or rather stayed thoroughly second-rate.
All agree that now there was a science of evolutionary biology, but it was a kind of evolutionary morphology, which was increasingly pushed out of the universities, if indeed it ever got in them, and became a museum subject. Evolution was much more a kind of popular science than anything else, and because it turned out that trying to trace phylogenies using evolutionary morphology and embryology ended in paradox more often than not, the best young biologists of the age turned increasingly away from evolutionary problems.
They took up other issues like cytology, embryology, and ultimately in the twentieth century, genetics. People like William Bateson, the English Mendelian, and Thomas Hunt Morgan, the great American fruit fly geneticist, started life as evolutionary biologists but found that the subject was getting them nowhere. So they turned to richer and more fertile fields.
I argue that this situation continued until the s and even into the s. Evolutionary biology was a second-rate subject, not one for a top-quality university mind. Students were steered away from it. It was only after the population geneticists, notably R. Haldane in England and Sewall Wright in America, had put genetics on a firm evolutionary basis from a theoretical point of view that it was possible to develop evolutionary theory as a university-based, mature, professional science Provine This finally occurred in the s and s, thanks particularly to the labors of such people as Theodosius Dobzhansky and his followers in America and to E.
Ford and others in Britain. By the s,. The question now is one of interpretation. Am I correct in my claims that what happened after Darwin until the s was indeed a disaster for evolutionary theory? The case is made fully in Ruse The eminent British historian of evolutionary biology, Peter Bowler, disagrees strongly.
He has detailed very carefully the work of the evolutionary morphologists in the latter decades of the nineteenth century and the first decades of the twentieth century Bowler , He shows rightly that there was a great deal of work that went on, and he argues that this was interesting and significant. More importantly, he argues that it was because of this work that evolutionary biology was able to take off and professionalize in the way that it did in the late s and s.
He believes that there is indeed a continuity, even though he himself has stressed that much of the work that was done around the turn of the century was not very Darwinian. He feels that whatever the regard for Darwins work, a basis was provided for the advances that were to come. I am obviously not the person to make a disinterested evaluation of this debate. I would simply say from my corner that I see no evidence to back Bowlers claim. I believe that the evolutionists of the s had themselves to break with what had gone before, and that they themselves set out deliberately to make a theory, not only at the conceptual level, but also at the social level.
One finds that few if any of them had any interest in morphology. Even the paleontologist of the group, G. Simpson , succeeded as a modern evolutionist because he was breaking away from the old fashions of searching desperately for phylogenies. He was developing and embracing a much newer, dynamic, causal picture of evolutionary change. Simpson in his way was just as much a revolutionary as the others.
Probably the time is not yet fully ripe to decide if the truth lies with me or with Bowler. Although much work has been done on the history of evolutionary theory, very little has been done at the meta-level on this grand a range. Most studies on evolutionary history are micro-studies on particular events or particular people. Few other than Bowler or myself who are now both long past the years of PhD thesis writing, an exercise that encourages micro-studies have attempted to look at the broader picture and to offer overall interpretations.
No doubt more work will be done on this, and nothing stimulates inquiry more than dispute. Quite probably, both Bowler and I will come through with our positions modified. However, at the moment we have an ongoing and as-yet-unresolved controversy about the nature of evolutionary theory. All agree that Darwin was crucially important in providing a theory of evolution through natural selection. All agree that, although Darwin was crucially important, his ideas were not picked up after the publication of the Origin in the s.
It was indeed not until the s and s that people became truly Darwinian and the modern theory of evolution was developed. All agree that between Darwin and the s a great deal of non-Darwinian biology was done, which drew heavily on German morphology and other roots. The question is Where does one go from here? Does one want to argue as does Bowler that this intermediary science was good quality science albeit non-Darwinian, and that it led in an important way to the modern theory of evolution?
Or does one argue as I do that. That it was second-rate, if science at all, and often was used simply as a vehicle for quasi-religious ideas, and that the development to the modern theory in the s and s took place only because the new practitioners turned their backs on or were ignorant of what had gone before?
That they have reached back rather across the years to Darwin himself? Here we have two very different pictures of evolutionary theory. In its history, time and more research will tell which is correct. If you are an evolutionist, that is to say, if you believe that all organisms came gradually by natural processes from one or a few forms as Darwin said , then it is almost inevitable that you will start to think about ultimate origins.
You will start to ask questions about how life itself came into being. Was it something that was seeded from elsewhere, or was it something that developed naturally in some fashion here on earth? Certainly the early evolutionists, Erasmus Darwin and Jean-Baptiste de Lamarck, thought long and hard about ultimate origins, both of them subscribing to some form of the venerable doctrine of spontaneous generation Farley Lamarck, for instance, believed that in pools of warm mud, lightening and heat and so forth would stir things up.
Worms and the like would come about instantaneously, and thus life would be on its path upward. This was a belief shared by other early evolutionists through to the first part of the nineteenth century. You find, for instance, that Robert Chambers the author of Vestiges of the Natural History of Creation thought that somehow life comes about instantaneously, and he was forever looking for lifelike forms in the inorganic world that he believed might be generated into living beings. At the time that Darwin wrote the Origin, however, the whole notion of spontaneous generation was coming under very heavy criticism, and as is well known the French biologist Louis Pasteur in the s was to drive the final nail into its coffin.
Darwin, a very skilled scientist, knew that he could only get into trouble if he subscribed to anything like spontaneous generation, and yet he knew he had no alternative. Wisely therefore, he realized that the best course of action was to say nothing at all, and so in the Origin the vital question of the origin of life is significant mainly by its total absence.
Darwin said nothing because he had nothing to say, and in many respects his strategy was very successful, because any question of lifes origin never became one of the focal points of debate after the Origin Ruse It was, however, a problem that would not go away, especially if spontaneous generation no longer seemed to be a viable option. It is generally agreed that the major breakthroughs on this topic came about in the s, when independently the English biochemist and geneticist J.
Haldane and the Russian biochemist A. Oparin put forward ideas about lifes origins. They suggested. But there would have been a kind of organic evolution leading up to functioning primitive life forms. These ideas of Haldane and Oparin received considerable support in the s, when researchers at the University of Chicago, Harold Urey and Stanley Miller , showed how it would be possible to make some of lifes basic building blocks amino acids naturally from inorganic compounds naturally, under experimental condition similar to what might have been expected back when life was supposedly formed.
Much work has gone on since then, although no one could say that the questions have been answered with unambiguous success. Indeed, the whole matter of the origin of life is today one of some considerable controversy Ruse b. On the one hand, we have some of the leading researchers admitting that we really do not yet know how life could come about.
One prominent researcher, using the metaphor of a detective story, writes We must conclude that we have identified some important suspects and, in each case, we have some ideas about the method they might have used. However, we are very far from knowing whodunit Orgel , p. On the other hand, we find critics who are contemptuous of supposed claims about the supposed origins of life. For instance, the eminent philosopher of religion Alvin Plantinga states that, in his opinion, we are, if anything, further away from solutions now than we were in the past.
He speaks of hypotheses about the origin of life as for the most part mere arrogant bluster, adding that given our present state of knowledge, I believe it is vastly less probable, on our present evidence, than is its denial Plantinga , p. Is this really so? It is useful to break the OparinHaldane hypothesis into a number of steps Freeman and Herron We begin first with the question of the conditions required for the natural creation of organic molecules, those that constitute the ultimate building blocks of life.
If conditions back when life is supposed to have begun some 3. The oxygen atmosphere that we have today would preclude that. However, it is thought that, around the time that life is supposed to have started, in fact the atmosphere on the earth was oxygen-free, somewhat laden with other gases such as methane, ammonia, carbon dioxide, and hydrogen sulfide.
These are just the ingredients that we need for making elementary molecules. Then, second, there is the production of complex molecules from inorganic substances. Mention has already been made of the work of Miller and Urey, and it is still thought that their work holds up well.
There would have been precisely the kinds of radiation, electrical storms, etc. Next in the OparinHaldane sequence you have the question of linking these primitive molecules into long macromolecules, to make the substances we find in cells today: proteins and nucleic acids. The problem is not so much the joining of the molecules this happens quite easily but keeping them joined long enough for them to start functioning. Quite possibly what happened was that the molecules.
This has been simulated. But how then do we move on the fourth step, to get the chain molecules to replicate themselves? Some suggest that the clays continue to play an important role. Crystals repeat themselves, building copies on templates although sometimes with mistakes built in. These mistakes then get repeated. Perhaps the organic molecules piggybacking on the crystals got repeated; then mistakes got built in, and eventually the molecules could themselves take over reproduction, dropping their supports.
Possibly, however, the molecules themselves could move directly to making proteins. It is thought that the key molecule here would be RNA, because in some organisms it is the only nucleic acid. It is capable of replicating itself and also of acting as a model for other cellular building blocks.
There are going to be more steps after this. For instance, one has to make a globular cell. It was here that Oparin spent most of his lifes work, as did a number of Americans, notably Sidney Fox They were showing how one could make self-contained spheres that can maintain and reproduce themselves. Possibly the organic molecules would work within these spheres. Later it is thought that other events had to occur. Most researchers today subscribe to the ideas of the American researcher Lynn Margulis , , who has argued that, to make more complex cells, one needed a kind of symbiotic relationship between more primitive cells.
The cell parts today, like mitochondria, perhaps once had an independent existence. Then they were incorporated within other cells and now remain there as part of a united whole. There is more after this. For instance, one needs the development of sexuality and things of this nature. I really do not think that even the greatest optimist could say that we are anywhere close to having a full and adequate picture of lifes origins. There are far too many gaps waiting to be filled in and unknowns that have not been properly addressed and answered.
On the other hand, this said, huge advances have been made in the past half century on this problem of lifes origin. Moreover, this is an area that is not stagnating, but rather where a great deal of effort is being put into exploring the various links. It is not a topic that scientists avoid because they have no ideas at all about how to tackle the problems. If anything, it is a more vigorous area than it has ever been before. It seems therefore that it would be foolish indeed to conclude with the critics that this is an area of great weakness for the evolutionist.
It is simply not true, as Plantinga claims, that we are further back now than we were before. Indeed, to the contrary, thanks to the coming of molecular biology we now are starting to have a full appreciation of the great problems that are involved in coming to an adequate theory of lifes origins. Recognizing the magnitude of problems is the first step toward solving them. Philosophers are notoriously unreliable when making forecasts about the future of science. But my suspicion is that in the next half century we will see even greater advances than before, and without confidently predicting that it will be possible to create life anew in the test tube in the laboratory, my suspicion is that we will at some point in the foreseeable future start to get really solid answers to the origin of life.
It is no longer the black hole for evolution that it was at the time for Charles Darwin. Let me move now to the central issue of modern evolutionary theory, namely the Darwinian mechanism of natural selection. Charles Darwin argued that more organisms are born than can possibly survive and reproduce.
There is consequently a struggle for existence. Then following this, given the naturally occurring variation in populations, there will be something analogous to the breeders form of artificial selection. This Darwin called natural selection: more organisms are born than can survive and reproduce, and those that are successful or fitter succeed because of variations they have that the losers do not have.
Overall, given enough time, this leads to evolutionary change. But it is important to note that for the Darwinian, this change is of a particular kind; namely, it is change in the direction of adaptation. Organisms have characteristics that enable them to survive and reproduce characteristics like the eye or hand.
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