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The period of Darwinism (1859-1882) 1 The development of evolutionary theory since Darwin – Darwinism The period of Darwinism (1859-1882) Exercise 1 (home group, individual work): Read the following text carefully. Your task is to fill in the missing words and phrases, which you know from your biology lessons. If you need help, you can... • …go back in the text or • …read further. If you have problems understanding the text, write down your questions! Charles Darwin was an enthusiastic natural scientist. He tried to write down all his observations of animals and plants and sought to explain them. After his expedition on the Beagle (fig. 1), which took five years, Charles Darwin recognized that there had to be an explanation other than creation by God for the diversity of life and for the similarities he observed between the organisms. Fig. 1: The research ship: the Beagle. © CNDP, 2009 In 1837 Darwin wrote down the theory of descent with___________________________ for the first time in his notebooks. The name of the theory derives from the Latin descendere (i.e. to descend) and means that organisms descended from a common ancestor and Fig. 2: Darwin collected animals. © CNDP, 2009 changed. Darwin developed this theory by collecting fossils and animals. He noticed that he could reproduce lines of related organisms by arranging them in such a way that there were very few modifications from one organism to the next. www.evolution-of-life.com Marcus Hammann (corresponding author) 2 The development of evolutionary theory since Darwin – Darwinism In the same year, Darwin described the theory of __________________________________________ of all organisms. Later he also included human beings – to the horror of many. However, Darwin initially wrote down this idea only in his notebooks. It was essential for him that all organisms on earth have a common origin. Fig. 3: Darwin draws a phylogenetic tree. © CNDP, 2009 In 1838, Darwin explained the change of the species by means of the theory of ______________________________. He was inspired to do so, when he read a book from Thomas R. Malthus about human population: “[F]ifteen months after I had begun my systematic enquiry, I happened to read for amusement Malthus on Population, and being well prepared to appreciate the struggle for existence which everywhere goes on from long-continued observation of the habits of animals and plants, it at once struck me that under these circumstances favorable variations would tend to be preserved, and unfavorable ones to be destroyed. The result of this would be the formation of a new Fig. 4: An example of the struggle for existence. © CNDP, 2009 species.” (Darwin, 1859) Moreover, Charles Darwin published an additional theory in his important publication ‘On the origin of species’ (1859): the theory of ____________________________. It says that the change of species takes place in small steps (gradually) and not in saltations (leaps). Darwin deduced gradualism from an old tradition in Natural Philosophy, according to which there are generally no saltations (leaps) in nature. However, also other researchers made contributions to the development of evolutionary theory, especially Henry W. Bates and Ernst Haeckel. www.evolution-of-life.com Marcus Hammann (corresponding author) 3 The development of evolutionary theory since Darwin – Darwinism In 1862, Henry W. Bates observed in the Amazon region that edible butterflies imitate the coloration of poisonous or inedible butterflies, when both species occur in the same habitat. He termed this phenomenon ____________________. When the appearance of poisonous butterflies varied geographically, Bates discovered the same variations among edible butterflies. Mimicry means imitation. Fig. 5: A drawing from Henry W. Bates. (in: Linn. Soc. 23:495-566, 1862; Source: www.wikipedia.org) In 1866, Ernst Haeckel described the _____________________________________: “During its rapid and short development, the organic individual repeats the most important modifications its ancestors had to pass through during their slow and long-lasting paleontological development according to the Fig. 6: Each column shows three embryonic steps of development of a species. Considering the first line reveals that the different species are very similar to each other in the beginning of the embryonic development. laws of inheritance and adaptation.” (Haeckel, 1874; Source: www.wikipedia.org) Five years later Charles Darwin published a further theory. He developed the theory of _______________________________________, with the intention to explain characteristics like the gorgeous tail of the peacock. At first sight it seems to be disadvantageous for the peacock, but it is favored by the peahens. The theory of natural selection was not a sufficient explanation for this phenomenon. www.evolution-of-life.com Marcus Hammann (corresponding author) Fig. 7: Darwin assumed that females have apparently a sense of beauty. © CNDP, 2009 4 The development of evolutionary theory since Darwin – Darwinism Exercise 2 (expert group, teamwork) Check your cloze texts and your reading comprehension for correctness. Subsequently answer the following questions: a) Which term (that Darwin himself never used) is used for Darwin’s first theory of 1837 as it is known today? You know this term from class. _____________________________________________________________________ _____________________________________________________________________ b) Why do nonpoisonous butterflies imitate the coloration of poisonous butterflies? Why was Charles Darwin encouraged by these findings? _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ c) Why couldn’t Charles Darwin explain the gorgeous tail of the peacock by natural selection? Find another explanation for the gorgeous tail of the peacock! _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ d) Give further examples for characteristics that developed by means of sexual selection. _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ www.evolution-of-life.com Marcus Hammann (corresponding author) 5 The development of evolutionary theory since Darwin – Darwinism Exercise 3 (expert group, individual work) Copy the terms you filled into the gaps of the cloze text (everything that is underlined) onto the ‘milestone-cards’ (see last page of the material). There is one card for each milestone from the period of Darwinism. Exercise 4 (home group, teamwork): Each of you is asked to present the milestones of his/her period to the other team members by attaching the milestone-cards chronologically to the time bar. The expert for the period of Darwinism starts. For each milestone-card, the expert explains, which person arrived at which insight by which means and how the insight changed evolutionary theory. Afterwards, the next expert follows until the time bar is completed. Exercise 5 (home group, teamwork): After completing the time bar, your team creates a concept map with as many connections as possible. 1.) Choose at least 12 milestones from the time bar (each period should be included). 2.) Write down the term from each milestone on a piece of paper. 3.) Arrange the pieces on a blank sheet so that the milestones which have a close connection lie close to each other. Consider what kind of relationship exists between the different milestones. The following advices my help you: The relation between two terms can be that … … one term is an example of the other term (i.e.: mimicry is an example of natural selection) … one term is part of the other term in the sense of a whole – part relationship (i.e.: chromosomes contain genes) … terms are superordinate or subordinate concepts (i.e. mutation and selection are evolutionary factors) www.evolution-of-life.com Marcus Hammann (corresponding author) 6 The development of evolutionary theory since Darwin – Darwinism 4.) If you are satisfied with the arrangement of the milestones and the relations between them, glue the pieces of paper on the blank sheet. 5.) Now draw arrows between the terms. 6.) Describe the relationship above the arrows. www.evolution-of-life.com Marcus Hammann (corresponding author) 7 The development of evolutionary theory since Darwin – Darwinism www.evolution-of-life.com Marcus Hammann (corresponding author) 8 The development of evolutionary theory since Darwin – Darwinism www.evolution-of-life.com Marcus Hammann (corresponding author) The period of Neo-Darwinism (1883-1907) 1 The development of evolutionary theory since Darwin – Neo-Darwinism The period of Neo-Darwinism (1883-1907) Exercise 1 (home group, individual work): Read the following text carefully. Your task is to fill in the missing words and phrases, which you know from your biology lessons. If you need help, you can... • go back in the text or • read further or • regard the figures carefully. If you have problems understanding the text, write down your questions! The term Neo-Darwinism was coined on the occasion of the revolutionary findings of the scientist August Weismann. In 1882, August Weismann declared that there is no _____________________________________ ____________________________________________. August Weismann conducted a spectacular experiment (see fig. 1), in order to test his hypothesis. He repeated the experiment over several generations of mice. In contrast, Charles Darwin believed in the idea, that acquired traits can be inherited; an idea that was first formulated by Jean-Baptiste de Lamarck around 1800. But how did August Weismann explain the findings of his experiments? He did further research. In 1885 he discovered that germ line cells are separated from somatic cells (body cells) very early in the embryonic development. Accordingly, he postulated the division between____________________________________. Fig. 1: The procedure of Weismann’s experiment. He repeated this experiment 19 times. The offspring of the subsequent matings provided the basis for the next experiment. But how did Weismann explain variability? He assumed _______________________ during the sexual reproduction to be the solution. He postulated maternal and paternal genetic material is combined in the form of particles. Figure 2 shows a drawing by August Weismann. www.evolution-of-life.com Marcus Hammann (corresponding author) 2 The development of evolutionary theory since Darwin – Neo-Darwinism It illustrates how he imagined the process of inheritance. Today we know that the process of inheritance is much more complicated. August Weismann had no knowledge of chromosomes and crossing-over. However, the scientist recognized correctly, that sexual reproduction is the cause of individual differences, which are the basis for natural selection. Weismann’s assumption represented another breach with traditional concepts in 1886. In that time many biologists believed that inheritance works like the coalescence of liquids. According to this idea, sexual reproduction leads to the uniformity in a species, but not to variability. Fig. 2: Original drawing from August Weismann. He supposed that maternal and paternal parts will be inherited as solid particles. (Fig. from A. Weismann: ”Essays upon heredity“ Vol. I & II, 1889) www.evolution-of-life.com Marcus Hammann (corresponding author) 3 The development of evolutionary theory since Darwin – Neo-Darwinism The scientist Hugo de Vries rediscovered Mendel’s laws around 1900 and popularized them. Thereby he became the founder of genetics. He reproduced the Mendelian experiments with the evening primrose (fig. 3) and explained the appearance of new variants after crossbreeding with the theory of ______________________. De Vries felt confident that his discovery of spontaneously occurring modifications in the genetic material – and not natural selection – explained the change of species. The next years Charles Darwin’s theory of natural selection receded into the background, while Hugo de Vries’ theory was mistaken to be the main mechanism of Fig. 3: Evening primrose. De Vries reproduced the Mendelian experiments with this plant. (Thomé, 1885; Source: www.wikipedia.org) evolution. Later it became apparent that mutations cannot completely account for evolutionary the change in species, but additional evolutionary mechanisms have to take effect, i.e. natural selection. In 1896, Henri Becquerel discovered radioactivity. This discovery enabled Marie and Pierre Curie in 1902 to determine geological time spans just like using a clock. In 1906 it was possible for the first time to determine the approximate age of the earth by radioactive measurements. They calculated that the earth is _____________________ years old. This finding surprised many scientists, because most of them estimated the age of the earth to be at the most a few thousand years, whereas Charles Darwins assumptions, however, were confirmed. He would have been very happy about this insight. www.evolution-of-life.com Marcus Hammann (corresponding author) Fig. 4:Our globe. (© Paul Schubert, earthe_01, CC-Lizenz (BY 2.0) http://creativecommons.org/licenses/by/2.0/de/deed.de; Source: www.piqs.de ) 4 The development of evolutionary theory since Darwin – Neo-Darwinism Exercise 2 (expert group, teamwork) Check your cloze texts and your reading comprehension for correctness. Subsequently answer the following questions: a) Describe the process of August Weismann’s experiment with mice. What was the finding of his experiment? _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ b) How does August Weismann explain this result? _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ c) What causes variability according to the hypothesis August Weismann’ formed in 1886? What fact was he not aware of in this time? Discuss the misconceptions of Weismann and explain his misunderstandings about the mechanism of inheritance. Think of meiosis! _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ d) Why was Hugo de Vries mistaken when he supposed that mutations are solely responsible for the development of new species? _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ e) Why would Charles Darwin – if he would have been alive at that time – have been very happy about the discovery in 1906? (If you cannot find the solution yet, ask the expert of Darwinism later in the home group.) _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ www.evolution-of-life.com Marcus Hammann (corresponding author) 5 The development of evolutionary theory since Darwin – Neo-Darwinism Exercise 3 (expert group, individual work) Copy the terms you filled into the gaps of the cloze text (everything that is underlined) onto the ‘milestone-cards’ (see last page of the material). There is one card for each milestone from the period of Neo-Darwinism. Exercise 4 (home group, teamwork): Each of you is asked to present the milestones of his/her period to the other team members by attaching the milestone-cards chronologically to the time bar. The expert for the period of Darwinism starts. For each milestone-card, the expert explains, which person arrived at which insight by which means and how the insight changed evolutionary theory. Afterwards, the next expert follows until the time bar is completed. Exercise 5 (home group, teamwork): After completing the time bar, your team creates a concept map with as many connections as possible. 1.) Choose at least 12 milestones from the time bar (each period should be included). 2.) Write down the term from each milestone on a piece of paper. 3.) Arrange the pieces on a blank sheet so that the milestones which have a close connection lie close to each other. Consider what kind of relationship exists between the different milestones. The following advices my help you: The relation between two terms can be that … … one term is an example of the other term (i.e.: mimicry is an example of natural selection). … one term is part of the other term in the sense of a whole – part relationship (i.e.: chromosomes contain genes). … terms are superordinate or subordinate concepts (i.e. mutation and selection are evolutionary factors). www.evolution-of-life.com Marcus Hammann (corresponding author) 6 The development of evolutionary theory since Darwin – Neo-Darwinism 4.) If you are satisfied with the arrangement of the milestones and the relations between them, glue the pieces of paper on the blank sheet. 5.) Now draw arrows between the terms. 6.) Describe the relationship above the arrows. www.evolution-of-life.com Marcus Hammann (corresponding author) 7 The development of evolutionary theory since Darwin – Neo-Darwinism www.evolution-of-life.com Marcus Hammann (corresponding author) The period of NeoDarwinism and Population Genetics (1908-1930) 1 The development of evolutionary theory since Darwin – Population Genetics The period of Neo-Darwinism and Population Genetics (1908-1930) Exercise 1 (home group, individual work): Read the following text carefully. Your task is to fill in the missing words and phrases, which you know from your biology lessons. If you need help, you can... • …go back in the text or • …read further. If you have problems understanding the text, write down your questions! In the early 20th century, the integration of Mendelism and Darwinism started. The rediscovery of Mendel’s laws around 1900 displaced the theory of natural selection by Charles Darwin. In 1908, Godfrey H. Hardy and Wilhelm R. Weinberg established the basis for this important integration of theories independent of each other. In 1908, Hardy attended a conference, at which the frequency of recessive characters was discussed. The scientist Yule stated that recessive factors (today better known as alleles) will disappear in the course of a few generations even if natural selection is absent because dominant factors (alleles) will establish themselves at any rate. Hardy disagreed with Yule’s statement, but he was not able to disprove it. He was quite unhappy about this. In the same year, he managed to develop a mathematical formula (see fig. 1). It says that allele frequencies in “ideal populations”, which means in the absence of factors like selection or mutation, will remain constant by means of random recombination (see example in fig. 1). This principle was later called the ______________________________distribution. www.evolution-of-life.com Marcus Hammann (corresponding author) 2 The development of evolutionary theory since Darwin – Population Genetics p² frequency of genotype BB + 2pq + frequency of genotypes Bb and bB q² = frequency of genotype bb Fig. 1: Example of use for the formula of Hardy and Weinberg. www.evolution-of-life.com Marcus Hammann (corresponding author) 1 3 The development of evolutionary theory since Darwin – Population Genetics Two years later, Thomas H. Morgan and his team studied the inheritance of white eyes in Drosophila (fig. 2). The team discovered that ________________________ are responsible for the inheritance. But soon a problem occurred: there were more character states than chromosomes. Thomas H. Morgan did further research and succeeded in solving the problem. The solution consisted in ____________________________. Thomas Morgan had to define them exactly because until then they were simply known as “units of heredity”. Fig. 2: Drosophila with red eyes. (© André Karwath, CC-Lizenz (BY 2.0) http://creativecommons.org/licenses/by/2.0/de /deed.de; Source: www.wikipedia.de ) In 1928, the scientist Frederick Griffith investigated the bacterium Streptococcus pneumoniae, which causes pneumonia in mammals. He worked with two different strains. The so-called S-strain (S means smooth) of the bacterium Streptococcus pneumoniae is characterized by a mucic capsule, which surrounds two connected cells. The other so-called R-strain (R means rough) has no mucic capsule. Griffith was surprised that he was able to obtain living pathogenic cells from the dead mice in experiment 4. The mice had obtained a mixture of pathogenic cells killed by using heat and living harmless cells (fig. 3). Griffith concluded that some chemical substance from the pathogenic cells had changed (transformed) the harmless cells. Thus, Griffith discovered the phenomenon of _______________________. Fig. 3: Frederick Griffith’s experiment. He drew his conclusions from experiment 4. www.evolution-of-life.com Marcus Hammann (corresponding author) 4 The development of evolutionary theory since Darwin – Population Genetics Sixteen years later, in the year 1944, Oswald T. Avery continued the experiment from Griffith. Avery succeeded in identifying the mysterious chemical substance, which transformed the harmless cells into pathogenic cells in the 4th experiment. He discovered the mysterious molecule responsible for inheritance: ___________. He made this discovery by relating his experiments to already existing findings of Frederick Griffith. Fig. 4: The experiment from Oswald T. Avery. He related his experiments to the findings of Frederick Griffith from the year 1928. www.evolution-of-life.com Marcus Hammann (corresponding author) 5 The development of evolutionary theory since Darwin – Population Genetics Exercise 2 (expert group, teamwork) Check your cloze texts and your reading comprehension for correctness. Subsequently answer the following questions: a) Imagine you are Godfrey Hardy and would like to persuade scientists like Yule that recessive and dominant alleles alone do not trigger evolution. Interpret figure 1 in order to support your argumentation. _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ b) How did Thomas H. Morgan solve the problem that there are more character states than chromosomes? _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ c) Describe Frederick Griffith’s experiments. What happened in experiment 4 (fig. 3) so that the R-cells killed the mice? _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ d) Using figure 4, explain, how Oswald T. Avery discovered the mysterious molecule of inheritance. _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ www.evolution-of-life.com Marcus Hammann (corresponding author) 6 The development of evolutionary theory since Darwin – Population Genetics Exercise 3 (expert group, individual work) Copy the terms you filled into the gaps of the cloze text (everything that is underlined) onto the ‘milestone-cards’ (see last page of the material). There is one card for each milestone from the period of population genetics. Exercise 4 (home group, teamwork): Each of you is asked to present the milestones of his/her period to the other team members by attaching the milestone-cards chronologically to the time bar. The expert for the period of Darwinism starts. For each milestone-card the expert explains, which person arrived at which insight by which means and how the insight changed evolutionary theory. Afterwards, the next expert follows until the time bar is completed. Exercise 5 (home group, teamwork): After completing the time bar, your team creates a concept map with as many connections as possible. 1.) Choose at least 12 milestones from the time bar (each period should be included). 2.) Write down the term from each milestone on a piece of paper. 3.) Arrange the pieces on a blank sheet so that the milestones which have a close connection lie close to each other. Consider what kind of relationship exists between the different milestones. The following advices my help you: The relation between two terms can be that … … one term is an example of the other term (i.e.: mimicry is an example of natural selection). … one term is part of the other term in the sense of a whole – part relationship (i.e.: chromosomes contain genes). … terms are superordinate or subordinate concepts (i.e. mutation and selection are evolutionary factors). www.evolution-of-life.com Marcus Hammann (corresponding author) 7 The development of evolutionary theory since Darwin – Population Genetics 4.) If you are satisfied with the arrangement of the milestones and the relations between them, glue the pieces of paper on the blank sheet. 5.) Now draw arrows between the terms. 6.) Describe the relationship above the arrows. www.evolution-of-life.com Marcus Hammann (corresponding author) 8 The development of evolutionary theory since Darwin – Population Genetics www.evolution-of-life.com Marcus Hammann (corresponding author) The period of Evolutionary Synthesis (1930-1950) 1 The development of evolutionary theory since Darwin – Evolutionary Synthesis The period of Evolutionary Synthesis (1930-1950) Exercise 1 (home group, individual work): Read the following text carefully. Your task is to fill in the missing words and phrases, which you know from your biology lessons. If you need help, you can... • …go back in the text or • …read further or • …regard the figures carefully. If you have problems understanding the text, write down your questions! Six prominent scientists, Theodosius G. Dobzhansky, Ernst Mayr, George Simpson, Julian S. Huxley, Bernhard Rensch and George L. Stebbins, have been particularly involved in further developing evolutionary theory. Their findings have been united in the period of evolutionary synthesis (Synthesis = combination). In the beginning of this time period, Ronald A. Fisher focused on sexual selection. Whereas Charles Darwin was able to observe sexual selection only, Fisher was now able to explain this evolutionary factor. He revealed that both the female trait ’preference‘ and the male trait ’ornament‘, i.e. the peacock’s tail, are coded genetically. Based on this assumption, he proposed the _________________-process. This hypothesis describes that male ornaments become bigger and/or more conspicuous by an automatism. Fig. 1: The fan-out of a peacock. (© Josi, Pfau, CC-Lizenz (BY 2.0) http://creativecommons.org/licenses/by/2.0/de/deed.de; Source: www.piqs.de ) The genes for the female trait ‘preference’ and the genes for the male trait ‘ornament’ are genetically associated, because females with a ‘preference’ for conspicuous ornaments mate with appropriate males and therefore the offspring bears both traits. Furthermore, he explained that once a male trait becomes too big and/or conspicuous, it will be restrained by other selection processes (i.e. increased conspicuousness for predators, increased susceptibility to disease). Fishers’ hypothesis on the runaway-process is able to account for the evolution of ornaments which are bigger and/or more conspicuous than required in the attempt to survive. www.evolution-of-life.com Marcus Hammann (corresponding author) 2 The development of evolutionary theory since Darwin – Evolutionary Synthesis Another important component of evolutionary biology was Ernst Mayrs’ definition of the biological__________________________ in 1942. Ernst Mayr was not the first scientist who dealt with this issue. However, in contrast to the morphological species concept, he emphasized the common gene pool (total number of all genes in a population) and the reproductive isolation of a species (fig. 2). Charles Darwin, the prime father of the evolutionary theory, used the term species but never defined it. Fig. 2: Very similar but still different: Willow Warbler (left; © Jörg Kretzschmar, 2009) and Chiffchaff (right; ©א, ) 2008, CC-Lizenz (BY 2.5) http://creativecommons.org/licenses/by/2.5/de/deed.de; Source: www.wikipedia.de In 1947, Bernhard Rensch studied the origin of new species (speciation). He differentiated two processes (fig. 3): the evolutionary change of various characteristics in each descendant (____________________) und the branching of a lineage into two or more descendant lines (____________________). Rensch came to this conclusion due to the discovery of fossils, which document these two processes of evolution. Furthermore the scientist explained the branching of two species by the mechanism of geographical isolation. This evolutionary mechanism cannot be attributed to mutation, recombination and selection and was first described by Ernst Mayr. Charles Darwin also considered geographical isolation to be a mechanism of speciation, but rejected this idea later. Today, additional mechanisms of speciation have been described by researchers. Fig. 3: Processes of anagenesis and cladogenesis. www.evolution-of-life.com Marcus Hammann (corresponding author) 3 The development of evolutionary theory since Darwin – Evolutionary Synthesis The mechanism of ____________________________ was first described by Sewall Wright in 1931 and was integrated into evolutionary theory in 1950. Wright’s discovery is also named Sewall-Wright-effect and characterizes the random fluctuation in the frequency of alleles. Therefore, the Sewall-Wright-effect is an evolutionary factor, which is independent of natural selection. The process described by Wright is especially important for small populations, where random changes in the frequency of alleles have serious influence. In the middle of the 20th century the contributions of the aforementioned scientists were integrated in _____________________________. This great theory combines classical Darwinism and modern findings of genetics, population genetics and systematics. Genetic drift, moreover, was identified as an additional evolutionary factor. According to evolutionary synthesis, mutation and recombination constantly cause genetic variations, whereas selection and genetic drift constrain these. The geneticist Theodosius Dobzhansky declared in these days: “Nothing in biology makes sense except in the light of evolution.” www.evolution-of-life.com Marcus Hammann (corresponding author) 4 The development of evolutionary theory since Darwin – Evolutionary Synthesis Exercise 2 (expert group, teamwork) Check your cloze texts and your reading comprehension for correctness. Subsequently answer the following questions: a) Ronald A. Fisher explained that a male ornament trait, which becomes too “expensive”, will be constrained by other selection processes. Which costs has a peacock to bear in his natural environment due to his ornate train? _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ b) Do organisms, which look externally similar, necessarily belong to the same species, according to Ernst Mayr’s biological species concept? _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ c) Why is the evolutionary factor discovered by Sewall Wright independent of natural selection? _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ d) Explain the citation of Theodosius Dobzhansky using the example of sexual dimorphism. _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ www.evolution-of-life.com Marcus Hammann (corresponding author) 5 The development of evolutionary theory since Darwin – Evolutionary Synthesis Exercise 3 (expert group, individual work) Copy the terms you filled into the gaps of the cloze text (everything that is underlined) onto the ‘milestone-cards’ (see last page of the material). There is one card for each milestone from the period of the evolutionary synthesis (just the two discoveries from Bernhard Rensch have to be noted on one card!). Exercise 4 (home group, teamwork): Each of you is asked to present the milestones of his/her period to the other team members by attaching the milestone-cards chronologically to the time bar. The expert for the period of Darwinism starts. For each milestone-card, the expert explains, which person arrived at which insight by which means and how the insight changed evolutionary theory. Afterwards, the next expert follows until the time bar is completed. Exercise 5 (home group, teamwork): After completing the time bar, your team creates a concept map with as many connections as possible. 1.) Choose at least 12 milestones from the time bar (each period should be included). 2.) Write down the term from each milestone on a piece of paper. 3.) Arrange the pieces on a blank sheet so that the milestones which have a close connection lie close to each other. Consider what kind of relationship exists between the different milestones. The following advices my help you: The relation between two terms can be that … … one term is an example of the other term (i.e.: mimicry is an example of natural selection). … one term is part of the other term in the sense of a whole – part relationship (i.e.: chromosomes contain genes). … terms are superordinate or subordinate concepts (i.e. mutation and selection are evolutionary factors). www.evolution-of-life.com Marcus Hammann (corresponding author) 6 The development of evolutionary theory since Darwin – Evolutionary Synthesis 4.) If you are satisfied with the arrangement of the milestones and the relations between them, glue the pieces of paper on the blank sheet. 5.) Now draw arrows between the terms. 6.) Describe the relationship above the arrows. www.evolution-of-life.com Marcus Hammann (corresponding author) 7 The development of evolutionary theory since Darwin – Evolutionary Synthesis www.evolution-of-life.com Marcus Hammann (corresponding author) The period of the Enhanced Evolutionary Eynthesis (from 1950) (Part 1) 1 The developm ent of evol utionary theory since Da rwin – Enhanced Evoluti onary Synthesis 1 The period of the Enhanced Evolutionary Synthesis (from 1950) (Part 1) Exercise 1 (home group, individual work): Read the following text carefully. Your task is to fill in the missing words and phrases, which you know from your biology lessons. If you need help, you can... • go back in the text or • read further. If you have problems understanding the text, write down your questions! The zoologist and marine biologist Adolf Remane established in 1952 the three main _________________________________________. They are a practical tool for research on phylogenetic relationships because they enable the researcher to differentiate between homologous and analogous traits. Homologies can be used to make inferences about kinship (fig. 1). Fig. 1: Homologous structures: Front limbs of salamander, turtle, crocodile, bird, bat, whale, mole, human (from left to right). (Wilhelm Leche, 1909; www.wikipedia.org) One year later James Watson and Francis Crick succeeded in clarifying the structure of DNA. At that time, the molecular components were already known. The discovery of the structure of DNA was possible due to the method of X-ray crystallography. Francis Crick was already familiar with this technique because he had investigated protein structures this Fig. 2: X-ray photograph way. Fig. 3: Structure of DNA. (Courtesy of Apers0n; Source: www.wikipedia.org) Crick introduced Watson to X-ray of DNA. (Courtesy of the National Institute of Health; Source: www.wikipedia.org) crystallography after Watson persuaded him that it is a worthy method for analysing the structure of DNA. A photograph of crystalline DNA www.evolution-of-life.com Marcus Hammann (corresponding author) 2 The developm ent of evol utionary theory since Da rwin – Enhanced Evoluti onary Synthesis 1 triggered an important insight (fig. 2). The photo was a result of the research of the X-ray expert Rosalind Franklin, who started her work in 1951 at the same college as Watson and Crick. From the photo, Watson concluded that the shape of a DNA molecule is a _________________________ (fig. 3). The researcher had seen X-ray photos of other helical molecules before. Subsequently, Watson and Crick reconstructed the exact plan of a DNA molecule with the aid of handmade wire models and finally published the DNA structure in 1953. Linus Pauling and Emile Zuckerkandl first postulated the concept of the ________________________________ in 1961. The discovery displays a measuring tool for estimating evolutionary distances. The basis for this concept is the following correlation: The longer two systematic entities are separated, the bigger is the number of differences in nucleotides Fig. 4: An illustration of the discovery from Pauling and Zuckerkandl. (Courtesy of Apers0n and Trojan respectively; Source: www.wikipedia.org) and changes in amino acids. The molecular clock corresponds with mutation rates of single genes or with differences between sequences in single proteins. This technique cannot be applied in every case, because not all genes or proteins possess a reliable average evolutionary rate. Therefore this method is hardly ever exact. The clock can be adjusted by the fossil record and enables the researcher to estimate e.g. at which time a specific speciation event took place. Even insights from geology played an important role for developing evolutionary theory further. In 1962, geology was revolutionized by the theory of ______________________________. The theory comprised the movement of plate tectonics and the forces which affect it. Furthermore, the theory explains the distribution of volcanoes, earthquakes, mountains, rock formations and the structures of the sea floor. The formation of these large-scale geological structures can be accounted for by the movement of the tectonic plates. As early as 1915, Alfred Wegener postulated the theory of continental drift based on his observation that the continents surrounding the Atlantic fit together like a puzzle. His theory was not accepted at that time because his assumptions on the driving force of plate tectonics proved wrong. Wegener hypothesized the tidal forces of the moon and the sun to cause this movement. www.evolution-of-life.com Marcus Hammann (corresponding author) 3 The developm ent of evol utionary theory since Da rwin – Enhanced Evoluti onary Synthesis 1 In 1962, Harry Hess and Robert Dietz found a plausible explanation for the driving force of plate tectonics, which is still accepted today. Hess and Dietz realized that convection (lat. convehere = to convey) in the mantle of the earth can passively pull and push the continents (see fig. 5). Fig. 5: Convection. A comparison. (The numbering belongs to exercise 2c). Another problem in evolutionary biology was the explanation of altruistic (unselfish) behavior. Already in the 19th century Charles Darwin, the father of evolutionary theory, described leaving (direct) offspring as the highest aim in life for each individual. But he would not have been able to explain, why Belding’s Ground Squirrels take a high risk of dying, when they warn other members of their Fig. 6: A Ground Squirrel watches for predators. (© Ute Steinbrecher, Wachposten, CC-Lizenz (BY 2.0) http://creativecommons.org/licenses/by/2.0/de/deed.de; Source: www.piqs.de ) species against predators. The animals utter a shrill warning cry, which does not only inform other members of their species about danger but also informs predators about the position of the alerter. Today it is known that the animals only risk their life when they are surrounded by closely related members of their species. For the relatives the chance of survival is increased enormously by the warning cry. www.evolution-of-life.com Marcus Hammann (corresponding author) 4 The developm ent of evol utionary theory since Da rwin – Enhanced Evoluti onary Synthesis 1 The behavior of Belding’s Ground Squirrel can be explained by the so-called kin selection. In 1964, William Hamilton developed a formula in order to predict under which circumstances unselfish behavior occurs. The basis for the formula and therefore the cause for altruistic behavior were already known in 1964: unselfish behavior depends on the degree of relationship. If the degree of relationship is known, it is possible to decide, if _______________________________ exists or not, due to the Hamilton-formula. Kin selection is a kind of natural selection because it increases the likelihood of passing on one’s genes (contains in the close relatives) to the next generation. Two years later, the zoologist Willi Hennig elaborated on the principle of _______________________________________, he had first described in 1950. This principle represents an application of Darwin’s theory of common descent to the discipline of systematics. Willi Hennig defined systematic groups as groups of organisms which share a common ancestor as well as all descendants of this ancestor. In contrast to this, classical systematics before Hennig often described groups, which did not comprise all descendants of a common ancestor (see fig. 7). Fig. 7: A cladogram. www.evolution-of-life.com Marcus Hammann (corresponding author) 5 The developm ent of evol utionary theory since Da rwin – Enhanced Evoluti onary Synthesis 1 Exercise 2 (expert group, teamwork) Check your cloze texts and your reading comprehension for correctness. Subsequently answer the following questions: a) Read up on the criteria of homology by Adolf Remane and give one example for each. _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ b) Specify the components of a DNA molecule. _____________________________________________________________________ _____________________________________________________________________ c) Explain the meaning of convection flow. Thereto, cut the pieces of the sentences on the page 8 and arrange them so that they are in accordance with the numbers in figure 5. _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ d) Explain why altruistic behavior is finally selfish. _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ e) Explain by means of figure 7, why reptiles do not exist as a systematic group in phylogenetic systematics. _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ www.evolution-of-life.com Marcus Hammann (corresponding author) 6 The developm ent of evol utionary theory since Da rwin – Enhanced Evoluti onary Synthesis 1 Exercise 3 (expert group, individual work) Copy the terms you filled into the gaps of the cloze text (everything that is underlined) onto the ‘milestone-cards’ (see last page of the material). There is one card for each milestone from the period of the enhanced evolutionary synthesis (part 1). Exercise 4 (home group, teamwork): Each of you is asked to present the milestones of his/her period to the other team members by attaching the milestone-cards chronologically to the time bar. The expert for the period of Darwinism starts. For each milestone-card, the expert explains, which person arrived at which insight by which means and how the insight changed evolutionary theory. Afterwards, the next expert follows until the time bar is completed. Exercise 5 (home group, teamwork): After completing the time bar, your team creates a concept map with as many connections as possible. 1.) Choose at least 12 milestones from the time bar (each period should be included). 2.) Write down the term from each milestone on a piece of paper. 3.) Arrange the pieces on a blank sheet so that the milestones which have a close connection lie close to each other. Consider what kind of relationship exists between the different milestones. The following advices my help you: The relation between two terms can be that … … one term is an example of the other term (i.e.: mimicry is an example of natural selection). … one term is part of the other term in the sense of a whole – part relationship (i.e.: chromosomes contain genes). … terms are superordinate or subordinate concepts (i.e. mutation and selection are evolutionary factors). www.evolution-of-life.com Marcus Hammann (corresponding author) 7 The developm ent of evol utionary theory since Da rwin – Enhanced Evoluti onary Synthesis 1 4.) If you are satisfied with the arrangement of the milestones and the relations between them, glue the pieces of paper on the blank sheet. 5.) Now draw arrows between the terms. 6.) Describe the relationship above the arrows. www.evolution-of-life.com Marcus Hammann (corresponding author) 8 The developm ent of evol utionary theory since Da rwin – Enhanced Evoluti onary Synthesis 1 … heats up and moves upward again. … and submerge in the mantle of the earth, where it melts and the hot melted material moves upward again. Hot material moves upward from the mantel of the earth … …and leads to the origin and separation of tectonic plates. Through convection water moves from the bottom to the surface … … cools down, moves sideward and sinks down… Where tectonic plates converge the cooler plate will submerge under the upper one... www.evolution-of-life.com Marcus Hammann (corresponding author) 9 The developm ent of evol utionary theory since Da rwin – Enhanced Evoluti onary Synthesis 1 www.evolution-of-life.com Marcus Hammann (corresponding author) The period of the Enhanced Evolutionary Synthesis (from 1950) (Part 2) 1 The developm ent of evol utionary theory since Da rwin – Enhanced Evoluti onary Synthesis 2 The period of the Enhanced Evolutionary Synthesis (from 1950) (Part 2) Exercise 1 (home group, individual work): Read the following text carefully. Your task is to fill in the missing words and phrases, which you know from your biology lessons. If you need help, you can... • …go back in the text or • …read further. If you have problems understanding the text, write down your questions! In the 1960s, the Japanese scientist Motoo Kimura investigated the degree of genetic variance in natural populations. He critically looked at the common assumption that mutations are either disadvantageous or advantageous because it contradicts the possibility of a great number of variations. Kimura applied a method, which enabled him to investigate the variance between individuals on the level of proteins. It turned out that the amino acid sequences of proteins in one population differed more often than previously assumed. Thus, Kimura concluded that most changes in the DNA do not have any influence on the survival and the reproduction rate of an organism. In other words, Kimura found out that most mutations are neutral. In 1968, he published his theory of ___________________evolution. This discovery did not contradict to the concept of natural selection, but rather added to existing evolutionary concepts. Not every mutation leads to phenotypical changes, which are subject to selection. Although Watson and Crick had analyzed the structure of DNA in the 1950s, it remained unclear, how this structure encodes information. Theoretical considerations suggested that three nucleotides contribute the information for one amino acid. Marshall Nirenberg and Heinrich Matthaei first succeeded in 1961 in synthesizing triplets (consisting of three nucleotides) outside a cell. They found out that RNA-triplets consisting of Uracil-nucleotides encode the amino acid phenylalanine. Soon they were able to synthesize RNA-triplets with nucleotide sequences in any combination. www.evolution-of-life.com Marcus Hammann (corresponding author) 2 The developm ent of evol utionary theory since Da rwin – Enhanced Evoluti onary Synthesis 2 The following figures illustrate an experiment for identifying the amino acid which is encoded by the triplet UUG. The preparation for the experiment is shown in figure 1. Then, 20 test-tubes are filled with defined components, with each test-tube containing different radioactively labeled amino acids. The test-tubes are left standing some time, so that the UUG-triplets can attach to the corresponding amino acid and to the ribosome. Afterwards, the main test run starts, composed of a Fig. 1: Illustration of the preparation. A total of 20 test-tubes are filled with the defined components. Each test-tube contains another radioactive labeled amino acid. maximum of 20 experiments (see figure 2). Next, the contents of each test-tube are filtered. The special filter retains only the ribosome and the attached components. Then, analyses of all 20 test-tubes reveal, in which test-tube radioactively labeled amino acid are retained. Fig. 2: The course of the test runs by Marshall and Nirenberg using the example of the triplet UUG. Two from a total of 20 experiments are illustrated (see arrow). The content of each test-tube will be filtered. www.evolution-of-life.com Marcus Hammann (corresponding author) 3 The developm ent of evol utionary theory since Da rwin – Enhanced Evoluti onary Synthesis 2 Nearly at the same time the scientist Har Gobind Khorana succeeded in synthesizing longer RNA-fragments outside the cell. Thus, the three scientists gained further insights into the nature of the codons. Thus the whole ________________________________ could be decoded in 1966. The genetecist Lynn Margulis rediscovered the ________________________________ in 1970. The theory was originally formulated by the Russian Merezhkowsky, who published it in 1910 without attracting further interest. The theory of endosymbiosis explains that chloroplasts and mitochondria of the eukaryotes are descendants from freely living prokaryotes, which entered the host cells through endosymbiosis at some point in the course of evolution. Fig. 3: The theory of endosymbiosis. www.evolution-of-life.com Marcus Hammann (corresponding author) 4 The developm ent of evol utionary theory since Da rwin – Enhanced Evoluti onary Synthesis 2 In 1977, Frederick Sanger developed the method of __________________________________. This method enabled researchers to determine the nucleotide sequence of a DNA molecule. The result is the sequence of the DNA strand which is complementary to the template. The basis of this method is the random assembly of a modified nucleotide (ddATP, ddCTP, ddTTP or ddGTP) during DNA-replication. It provokes the termination of the synthesis of the amplified strand, because the 3’-OH-end for the attachment of the next nucleotide is lacking. This results in many DNA fragments of different length, which can be separated by size through gel electrophoresis. Radioactive bands can be made visible (fig. 4) through autoradiography. Fig. 4: The method of DNA sequencing according to Frederick Sanger. www.evolution-of-life.com Marcus Hammann (corresponding author) 5 The developm ent of evol utionary theory since Da rwin – Enhanced Evoluti onary Synthesis 2 Another important step in the further development of evolutionary theory was the integration of the developmental biology, which deals with the development from the zygote to the complete organism. In 1980, the scientists Edward Lewis, Eric Wieschaus and Christiane Nüsslein-Volhard discovered the so called homeotic genes, which control embryonic development. These genes determine where, when and how specific segments of the body, like e.g. eyes or extremities, develop in an organism. Edward Lewis found the first of these genes when he investigated a Drosophila mutant bearing two instead of one pair of wings (fig. 5). Meanwhile, ________________________________ have been found in many different species. It became clear that particular nucleotide sequences (so-called ‘homeoboxes’) of these genes are identical or very similar in many species. A B Fig. 5: A Drosophila wild type B Drosophila mutant, bearing two instead of one pair of wings. © Markus Tögel, Werner Mangerich, Prof. Dr. Achim Paululat (University of Osnabrück), 2010 In 1982, John Maynard Smith made another important contribution. He applied the game theory, commonly used in economics, in order to explain behavioral patterns from an evolutionary perspective. Often, it can be observed that individuals of a species use different behavioral strategies in identical contexts. The game theory allows for predicting, when alternative behavioral strategies can exist in parallel and when one strategy displaces the other. Strategies, which stand up to alternative behavioral strategies and resist change, are called ________________________________ (ESS). By means of applying game theory and identifying evolutionary stable strategies it was possible to explain behavioral strategies, which had hitherto been unable to explain from the perspective of individual selection alone. www.evolution-of-life.com Marcus Hammann (corresponding author) 6 The developm ent of evol utionary theory since Da rwin – Enhanced Evoluti onary Synthesis 2 Exercise 2 (expert group, teamwork) Check your cloze texts and your reading comprehension for correctness. Subsequently answer the following questions: a) Because of the nature of the genetic code some point mutations do not result in a different gene product. Use the codon table to find out, at which positions of a nucleotide triplet neutral mutations can occur! Give an example. _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ b) Which amino acid is encoded by the triplet UUG? How did Nirenberg and Matthaei discover this? Explain how the experiment was conducted with the aid of the text and the figures. _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ c) Use figure 3 to explain, how the theory of endsymbiosis explains the formation of cells with mitochondria and chloroplasts. _____________________________________________________________________ _____________________________________________________________________ ____________________________________________________________________ _____________________________________________________________________ d) Use the example of the fly with two pairs of wings in order to explain the function of homeotic genes. _____________________________________________________________________ _____________________________________________________________________ ____________________________________________________________________ www.evolution-of-life.com Marcus Hammann (corresponding author) 7 The developm ent of evol utionary theory since Da rwin – Enhanced Evoluti onary Synthesis 2 Exercise 3 (expert group, individual work) Copy the terms you filled into the gaps of the cloze text (everything that is underlined) onto the ‘milestone-cards’ (see last page of the material). There is one card for each milestone from the period of the enhanced evolutionary synthesis (part 2). Exercise 4 (home group, teamwork): Each of you is asked to present the milestones of his/her period to the other team members by attaching the milestone-cards chronologically to the time bar. The expert for the period of Darwinism starts. For each milestone-card, the expert explains, which person arrived at which insight by which means and how the insight changed evolutionary theory. Afterwards, the next expert follows until the time bar is completed. Exercise 5 (home group, teamwork): After completing the time bar, your team creates a concept map with as many connections as possible. 1.) Choose at least 12 milestones from the time bar (each period should be included). 2.) Write down the term from each milestone on a piece of paper. 3.) Arrange the pieces on a blank sheet so that the milestones which have a close connection lie close to each other. Consider what kind of relationship exists between the different milestones. The following advices my help you: The relation between two terms can be that … … one term is an example of the other term (i.e.: mimicry is an example of natural selection). … one term is part of the other term in the sense of a whole – part relationship (i.e.: chromosomes contain genes). … terms are superordinate or subordinate concepts (i.e. mutation and selection are evolutionary factors). www.evolution-of-life.com Marcus Hammann (corresponding author) 8 The developm ent of evol utionary theory since Da rwin – Enhanced Evoluti onary Synthesis 2 4.) If you are satisfied with the arrangement of the milestones and the relations between them, glue the pieces of paper on the blank sheet. 5.) Now draw arrows between the terms. 6.) Describe the relationship above the arrows. www.evolution-of-life.com Marcus Hammann (corresponding author) 9 The developm ent of evol utionary theory since Da rwin – Enhanced Evoluti onary Synthesis 2 www.evolution-of-life.com Marcus Hammann (corresponding author)