Mechanisms & Evidence of Evolution PDF

General Biology 2 Lesson 3 Mechanisms of Evolution Prepared by: JOAN A. RIPARIP Learning Objectives At the end of the lesson, you should be able to: a. Trace the development of evolutionary thought b. Explain the mechanisms that produce change in populations from generation...

General Biology 2 Lesson 3 Mechanisms of Evolution Prepared by: JOAN A. RIPARIP Learning Objectives At the end of the lesson, you should be able to: a. Trace the development of evolutionary thought b. Explain the mechanisms that produce change in populations from generation to generation (e.g. Artificial selection, natural selection, genetic drift, mutation, recombination)  “Going back to Evolution your own roots “ After all, every turning point in studying biology will have us look into our origins. This means looking at how our common ancestors came to be to how life has diversified to be what it is today. A deeper insight about evolution can help us understand how all these came to be. Ancient Views on Species Species Were Static And Unchanging 18th Century Evolution Ideas The naturalist Georges-Louis Leclerc Comte de Buffon, who observed that various geographic regions have different plant and animal populations even when the environments are similar. It was also accepted that there were extinct species Geological Perspectives James Hutton, a Scottish naturalist, proposed that geological change occurred gradually by the accumulation of small changes from processes operating like they are today over long periods of time Hutton's view was popularized in the nineteenth century by the geologist Charles Lyell who became a friend to Darwin Charles Lyell's Influence on Darwin Lyell's ideas were influential on Darwin's thinking: Lyell's notion of the greater age of Earth gave more time for gradual change in species, and the process of change provided an analogy for gradual change in species. Lamarck's Mechanism for Evolution In the early nineteenth century, Jean- Baptiste Lamarck published a book that detailed a mechanism for evolutionary change. This mechanism is now referred to as an inheritance of acquired characteristics by which modifications in an individual are caused by its environment, or the use or disuse of a structure during its lifetime, could be inherited by its offspring and thus bring about change in a species.  Four Forces or Mechanisms of Evolution Natural Genetic Gene Flow Mutation Selection Drift (Migration) Natural Selection The actual mechanism for evolution was independently conceived of and described by two naturalists, Charles Darwin and Alfred Russell Wallace, in the mid-nineteenth century. Darwin observed species of organisms on different islands that were clearly similar, yet had distinct differences.  Darwin’s Finches: Darwin observed that beak shape varies among finch species. He postulated that the beak of an ancestral species had adapted over time to equip the finches to acquire different food sources. This illustration shows the beak shapes for four species of ground finch: 1. Geospiza magnirostris (the large ground finch), 2. G. fortis (the medium ground finch), 3. G. parvula (the small tree finch), and 4. Certhidea olivacea (the green-warbler finch). Natural Selection Darwin imagined that the island species might be all species modified from one original mainland species. In 1860, he wrote, "Seeing this gradation and diversity of structure in one small, intimately related group of birds, one might really fancy that from an original paucity of birds in this archipelago, one species had been taken and modified for different ends."  Natural Selection Natural selection, Darwin argued, was an inevitable outcome of three principles that operated in nature. First, the characteristics of organisms are inherited, or passed from parent to offspring. Second, more offspring are produced than are able to survive; in other words, resources for survival and reproduction are limited. Third, offspring vary among each other in regard to their characteristics and those variations are inherited.  Natural Selection Example Darwin's grand idea of evolution by natural selection is relatively simple but often misunderstood. To find out how it works, imagine a population of beetles. 1. There is variation in traits. For example, some beetles are green and some are brown. 2. There is differential reproduction. Since the environment can't support unlimited population growth, not all individuals get to reproduce to their full potential. In this example, green beetles tend to get eaten by birds and survive to reproduce less often than brown beetles do.  Natural Selection 3. There is heredity. The surviving brown beetles have brown baby beetles because this trait has a genetic basis. 4. End result: The more advantageous trait, brown coloration, which allows the beetle to have more offspring, becomes more common in the population. If this process continues, eventually, all individuals in the population will be brown. Natural Selection If you have variation, differential reproduction, and heredity, you will have evolution by natural selection as an outcome. Mutation Mutation-this is a change in the DNA sequence of the gene. Mutation is a source of new alleles in the population. A mutation can change one allele into another, but the net effect is change in frequency. The change in frequency resulting from mutation is small, so its effect on evolution is small also unless it interacts with one of the other factors such as selection. Mutation The outcomes or effect of mutation in an organisms’ phenotype or appearance are as follows: a. It may affect the phenotype of organism in a way that gives it reduced fitness- lower likelihood of survival, resulting in fewer offspring. b. It may produce a phenotype with a beneficial effect on fitness c. Neutral mutations will have no effect on fitness. Mutation A Mutation occurs when a DNA gene is damaged or changed in such a way as to alter the genetic message carried by that gene. A Mutagen is an agent of substance that can bring about a permanent alteration to the physical composition of a DNA gene such that the genetic message is changed. Mutation Is there a harmful mutation? Beneficial Mutation Some mutations have a positive effect on the organism in which they occur. They lead to new versions of proteins that help organisms adapt to changes in their environment. Beneficial mutations are essential for evolution to occur. They increase an organism’s changes of surviving or reproducing, so they are likely to become more common over time Harmful Mutation Any random change in a gene's DNA is likely to result in a protein that does not function normally or may not function at all. Harmful mutations may cause genetic disorders or cancer. Mutation It should be noted that mutation is the ultimate source of genetic variation in all populations – new alleles, and therefore, new genetic variations arise through mutation,  Genetic Drift Genetic drift is a mechanism of evolution. It refers to random fluctuations in the frequencies of alleles from generation to generation due to chance events. Genetic drift can cause traits to be dominant or disappear from a population. The effects of genetic drift are most pronounced in small populations.  Genetic Drift Genetic drift, also called genetic sampling error or Sewall Wright effect, a change in the gene pool of a small population that takes place strictly by chance. Genetic drift can result in genetic traits being lost from a population or becoming widespread in a population without respect to the survival or reproductive value of the alleles involved. Genetic Drift Genetic Drift Image source: By Gabi Slizewska Genetic Drift  Gene Flow Gene flow is the exchange of alleles between two or more populations. For this reason it is sometimes referred to as allele flow or gene migration. While migrating animals often carry new alleles from one population to another, they must interbreed with the new population for gene flow to occur. Gene Flow  Recombination Recombination is a process by which pieces of DNA are broken and recombined to produce new combinations of alleles. This recombination process creates genetic diversity at the level of genes that reflects differences in the DNA sequences of different organisms. Recombination is an integral part of the complex process of meiosis in sexually reproducing organisms. It results in a crossing over between pairs of genes along a chromosome, which are revealed in appropriate matings Recombination  Summary The factors that can change the allele frequencies of a population are: Natural selection works by selecting for alleles that confer beneficial traits or behaviors, while selecting against those for deleterious qualities. Mutations introduce new alleles into a population. Genetic drift is a mechanism of evolution in which allele frequencies of a population change over generations due to chance (sampling error). Genetic drift occurs in all populations of non-infinite size, but its effects are strongest in small populations.  Summary Gene flow tends to increase the similarity between remaining populations of the same species because it makes gene pools more similar to one another. Like mutation, recombination is an important source of new variation for natural selection. However, also like mutation, recombination places a genetic load upon the population.  SEATWORK #3 Why is understanding evolution important? Describe the effects of evolution on the diversity of population Do you think genetic drift would happen more quickly on an island or on the mainland? Why?  Understanding evolution is important. Understanding evolution helps us solve biological problems that impact our lives.... To control hereditary diseases in people, researchers study the evolutionary histories of the disease-causing genes. In these ways, a knowledge of evolution can improve the quality of human life.  It is conceivable that, in such a context, the mechanisms underlying behavior may be of evolutionary importance, because mechanisms can affect the probabilities with which phenotypes arise and, hence, the likelihood of alternative evolutionary forces. General Biology 2 Lesson 3 Evidence of Evolution Prepared by: JOAN A. RIPARIP Learning Objectives At the end of the lesson, you should be able to: a. Explain evidences of evolution (e.g., biogeography, fossil record, DNA/protein sequences, homology, and embryology) b. Infer evolutionary relationships among organisms using the evidence of evolution INTRODUCTION Darwin’s theory of evolution was eventually recognized when scientists were able to supply verifications that Darwin himself had been unable to specify. Darwin’s idea of evolution has been improved by new evidence that have been gathered by modern scientists. Natural selection gives us with an outline in understanding the ideologies of evolution. Moreover still, modern scientists are at an interminable expansion on collecting data and evidence that may verify or invalidate the information about evolution of life that we have now. And these pieces of evidence are significant in the field of biology.  Activity In the activity you will appreciate a body structure that is present in us and in some organisms related to humans “What a Thumb Can Do For You”  Activity: What a Thumb Can Do For You Do you understand how important your thumbs are? Only primates have hands capable of grasping objects. The grasp is created possible by the opposable thumbs. Are you aware that you simply perform plenty of tasks using your thumb and fingers? have you ever experienced doing a series of tasks without the help of your thumb? Ask a member of your family to tape your thumbs to the palms of each hand with masking tape. Be cautious not to wrap the tape too tightly because it will cut off the blood circulation to your hand. EVIDENCES OF EVOLUTION A. Fossils B. Comparative Embryology C. Comparative Anatomy D. Molecular Biology E. Biogeography  A. Fossils Fossils document the existence of now-extinct past species that are related to present-day species. Fossils are the preserved remains, or traces of remains, of ancient organisms. Fossils are preserved remnants of once living organisms trapped in rocks A. Fossils Most fossils are formed in sedimentary rock. They are rocks. A fossil can preserve an entire organism or just part of one. Bones, shells, feathers, and leaves can all become fossils. Paleontologists (a specialist in the study of the forms of life existing in prehistoric or geologic times), use the fossils found in rocks to track the evolutionary history of many organisms.  Figure 1. The different fossils remains of Homo luzonensis from Late Pleistocene sediments at Callao Cave. a, holotype CCH6: postcanine maxillary teeth in occlusal (left) and buccal (right) aspects, b, left P3 or P4 CCH8: occlusal (left) and buccal (right) aspects, c, right M3 CCH9: occlusal (top) and buccal (bottom) aspects d, juvenile femoral shaft CCH7 (anterior, lateral, posterior aspects. e, distal manual phalanx CCH5 (dorsal, lateral/medial, palmar aspects) f, intermediate manual phalanx CCH2 (dorsal, lateral, palmar aspects).g, 3rd metatarsal discovered in 2007 h, intermediate pedal phalanx CCH3 (dorsal, medial, plantar aspect)..) i, proximal pedal phalanx CCH4 (dorsal, lateral). Source: A new species of Homo from the Late Pleistocene of the Philippines, Nature, 2019 B. EMBRYOLOGY? What is EMBRYOLOGY? Embryology is a branch of science that is related to the formation, growth, and development of embryo. It deals with the prenatal stage of development beginning from formation of gametes, fertilization, formation of zygote, development of embryo and fetus to the birth of a new individual.  B. EMBRYOLOGY? Embryology gives evidence of relatedness between now widely different groups of organisms. An embryo is an organism in its initial phases of development.  Scientists observed that at some point during the development process, embryos of many different animals appeared so similar that it was difficult to tell them apart. Embryos of different vertebrates look much more similar than the animals do at later stages of life. Rows I, II, and III illustrate the development of the embryos of fish on the far left, salamander, tortoise, chick, hog, calf, rabbit, and human on the far right, from the earliest to the latest stages.  During development, at some time all vertebrates have a supporting dorsal rod, called a notochord, and demonstrate paired pharyngeal pouches. This could indicate that an organism passes through some of the embryonic stages that its ancestors passed through. Then numerous variations occur in ways appropriate to an organism’s final form.  C. Anatomical Evidence In comparing the anatomy and the development of organisms, it shows a unity of plan among those that are closely related. The more body structures that two species have in common, the more closely they are related. It adopts the idea of “descent from a common ancestor”.  C. Anatomical Continuation What is DESCENT? Descent is a concept in evolutionary biology applicable when one species is the ancestor of two or more species later in time. Similar structures in different species irrespective of their functions are called homologous structures.  C. Anatomical Continuation Homology indicate descent from common ancestor. The limb skeletons of vertebrates are homologous structures. Homologous structures are similar physical features in organisms that share a common ancestor, but the features serve completely different functions.  C. Anatomical Continuation Analogous structures are structures which are different in appearance but have the similar function. Analogy does not indicate common ancestry. Examples of are the limbs of insects and mammals, and wings of butterflies and birds.  C. Anatomical Continuation Vestigial structures seem like to give more evidence for evolutionary change. Vestigial structures are anatomical features that are usually reduced and have no function in many organisms. C. Anatomical Continuation Vestigial are organs that were previously functional in the ancestors of the species but are only remnants in the present-day species. For example, skeletal extremities discovered in certain snakes have no known use to these animals. In humans, appendix is thought to have no use, but in other mammals it aids in the digestion of cellulose. C. Anatomical Continuation  D. Biochemical Evidence Biochemical evidence of evolution is based on the fact that certain enzymes and chemical processes are found in the cells of all or nearly all life on Earth.  1. DNA/Nucleic acids Living organisms shared numerous related biochemical molecules, such as DNA, ATP, amino acids, and enzymes. This finding supports descent from a common ancestor. The more closely linked organisms are the more related is their biochemical genetic makeup. Each branch represents the emergence of new traits that separate one group of organisms from the rest. The cladogram in the figure shows how humans and apes are related based on their DNA sequences. Cladogram of Humans and Apes. This cladogram is based on DNA comparisons. It shows how humans are related to apes by descent from common ancestors. Humans are most closely related to chimpanzees and Bonobo (our common ancestor existed most recently). We are less closely related to gorillas, and even less closely related to Orangutan.  2. Proteins Proteins are molecules that are used to build up and repair body parts. Scientists believe that the more similar the structure of protein molecules of different organisms is, the more related they are and the more recent the existence of their common ancestor. Unrelated species have different amino acids. E. Biogeography Biogeography is the study of the geographic distributions of organisms. Darwin’s trip around South America allowed him to observe the diversity of organisms in different areas and the resemblance of such species of birds and tortoises in an island to nearby mainland. E. Darwin believed that the group of organisms in each island is adapted to a distinct way of life. The common ancestors of these organisms had come from one place, expanding out into other accessible regions E. Pangolins share similar characteristics with anteaters and armadillos E. E. E. Source: http://www.differencebetween.net/science/nature/animals-nature/difference-between-armadillo-and-pangolin/ E. Biogeography of Camels: E. Island Biogeography Figure 9.3.79.3.7: Galápagos finches differ in beak size and shape, depending on the type of food they eat. Those eating buds and fruits have the largest beaks. Insect and grub eaters have narrower beaks THANK YOU