Evolution plays a pervasive role in shaping the form and function of all biological molecules and organismsStudents should be able to explain and apply the core concepts underlying the theory of evolution, including the process of natural selection and its molecular basis, and evidence supporting the theory of evolution. Show
The learning goals below are categorized as introductory A, intermediate B and upper C. 1. The significance of evolutionEvolution is genetic change within a population over time. Understanding evolutionary processes and the supporting evidence is an integral part of the molecular life sciences. It explains many present day issues, such as crop availability and pesticide resistance in agriculture, vaccine and drug development in medicine and regulatory mechanisms in cellular, developmental and behavioral biology. Associated learning goals
2. Mechanisms of evolutionMany mechanisms may drive evolution. These include mutation, migration (gene flow), genetic drift (chance changes from generation to generation) and natural selection. Associated learning goals
3. Natural selection is a key evolutionary mechanismEvolution by natural selection results from differential reproductive success, where individuals with certain heritable traits are more successful. The fitness of an individual and its genotype is directly determined by its relative reproductive success. The fittest individuals will pass their genes to more offspring, driving the evolution of the population. In this way, the population becomes better-suited (adapted) to its environment. Multiple lines of evidence support evolution by natural selection, including the fossil record, homologies and direct observation in laboratory and field studies. Associated learning goals
4. The molecular basis of evolutionOrganismal traits are determined at the genetic and epigenetic level. Molecular modifications at these levels may determine the RNA and protein expression patterns in a cell, influencing the phenotype of the organism. Genetic modifications can also arise from the acquisition of new genetic material via processes such as horizontal gene transfer, endosymbiosis and viral vector transfer. Transmission of these heritable alterations may lead to changes in the genetic composition of a population, thereby driving evolution. Associated learning goals
This drawing was created in 1848, but it's likely that you recognize the animal it depicts as a horse. Although horses haven't changed that much since this drawing was made, they have a long evolutionary history during which they changed significantly. How do we know?
The answer lies in the fossil record. Evidence from FossilsFigure \(\PageIndex{2}\): Evolution of the Horse. The fossil record reveals how horses evolved. The lineage that led to modern horses (Equus) grew taller over time (from the 0.4 m Hyracotherium in early Eocene to the 1.6 m Equus). This lineage also developed longer molar teeth and the degeneration of the outer phalanges on the feet.Fossils are a window into the past. They provide clear evidence that evolution has occurred. Scientists who find and study fossils are called paleontologists. How do they use fossils to understand the past? Consider the example of the horse, outlined in figure \(\PageIndex{2}\). Fossils spanning a period of more than 50 million years show how the horse evolved. The oldest horse fossils show what the earliest horses were like. They were only 0.4 m tall, or about the size of a fox, and they had four long toes. Other evidence shows they lived in wooded marshlands, where they probably ate soft leaves. Over time, the climate became drier, and grasslands slowly replaced the marshes. Later fossils show that horses changed as well.
Evidence from Living SpeciesScientists can learn a great deal about evolution by studying living species. They can compare the anatomy, embryos, and DNA of modern organisms to help understand how they evolved. Comparative AnatomyFigure \(\PageIndex{3}\): Mammals (such as cats and whales) have homologous limb structures - with a different overall look but the same bones. Insects (such as praying mantis and water boatman) also have homologous limbs. Cat legs and praying mantis legs are analogous - looking similar but from different evolutionary lineages.Comparative anatomy is the study of the similarities and differences in the structures of different species. Similar body parts may be homologous structures or analogous structures. Both provide evidence for evolution. Homologous structures are structures that are similar in related organisms because they were inherited from a common ancestor. These structures may or may not have the same function in the descendants. Figure \(\PageIndex{3}\) shows the upper appendages of several different mammals. They all have the same basic pattern of bones, although they now have different functions. All of these mammals inherited this basic bone pattern from a common ancestor. Analogous structures are structures that are similar in unrelated organisms. The structures are similar because they evolved to do the same job, not because they were inherited from a common ancestor. For example, the wings of bats and birds, shown in the figure that follows, look similar on the outside and have the same function. However, wings evolved independently in the two groups of animals. This is apparent when you compare the pattern of bones inside the wings. Comparative EmbryologyComparative embryology is the study of the similarities and differences in the embryos of different species. Similarities in embryos are likely to be evidence of common ancestry. All vertebrate embryos, for example, have gill slits and tails. All of the embryos in Figure \(\PageIndex{4}\), except for fish, lose their gill slits by adulthood, and some of them also lose their tail. In humans, the tail is reduced to the tail bone. Thus, similarities organisms share as embryos may no longer be present by adulthood. This is why it is valuable to compare organisms in the embryonic stage. Figure \(\PageIndex{4}\): 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.Vestigial StructuresStructures like the human tail bone are called vestigial structures. Evolution has reduced their size because the structures are no longer used. The human appendix is another example of a vestigial structure. It is a tiny remnant of a once-larger organ. In a distant ancestor, it was needed to digest food, but it serves no purpose in the human body today. Why do you think structures that are no longer used shrink in size? Why might a full-sized, unused structure reduce an organism’s fitness? Comparing DNADarwin could compare only the anatomy and embryos of living things. Today, scientists can compare their DNA. Similar DNA sequences are the strongest evidence for evolution from a common ancestor. Look at the diagram in Figure \(\PageIndex{5}\). The diagram is a cladogram, a branching diagram showing related organisms. 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. Figure \(\PageIndex{1}\): Figure \(\PageIndex{5}\): 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.Evidence from BiogeographyBiogeography is the study of how and why organisms live where they do. It provides more evidence for evolution. Let’s consider the camel family as an example. Biogeography of Camels: An ExampleToday, the camel family includes different types of camels (Figure \(\PageIndex{6}\)). All of today’s camels are descended from the same camel ancestors. These ancestors lived in North America about a million years ago. Early North American camels migrated to other places. Some went to East Asia via a land bridge during the last ice age. A few of them made it all the way to Africa. Others went to South America by crossing the Isthmus of Panama. Once camels reached these different places, they evolved independently. They evolved adaptations that suited them for the particular environment where they lived. Through natural selection, descendants of the original camel ancestors evolved the diversity they have today. Figure \(\PageIndex{6}\). Camel Migrations and Present-Day Variation. Members of the camel family now live in different parts of the world. Dromedary camels are found in Africa, Bactrian camels in Asia, and Llamas in South America. They differ from one another in a number of traits. However, they share basic similarities. This is because they all evolved from a common ancestor. What differences and similarities do you see?Island BiogeographyThe biogeography of islands yields some of the best evidence for evolution. Consider the birds called finches that Darwin studied on the Galápagos Islands (Figure \(\PageIndex{7}\))). All of the finches probably descended from one bird that arrived on the islands from South America. Until the first bird arrived, there had never been birds on the islands. The first bird was a seed eater. It evolved into many finch species, each adapted for a different type of food. This is an example of adaptive radiation. This is the process by which a single species evolves into many new species to fill available ecological niches. Figure \(\PageIndex{7}\): 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 beaksEyewitnesses to EvolutionIn the 1970s, biologists Peter and Rosemary Grant went to the Galápagos Islands to re-study Darwin’s finches. They spent more than 30 years on the project, but their efforts paid off. They were able to observe evolution by natural selection actually taking place. While the Grants were on the Galápagos, a drought occurred, so fewer seeds were available for finches to eat. Birds with smaller beaks could crack open and eat only the smaller seeds. Birds with bigger beaks could crack open and eat seeds of all sizes. As a result, many of the smaller-beaked birds died in the drought, whereas birds with bigger beaks survived and reproduced. As shown in Figure \(\PageIndex{8}\), within 2 years, the average beak size in the finch population increased. In other words, evolution by natural selection had occurred. Figure \(\PageIndex{8}\). Evolution of Beak Size in Galápagos Finches. The left graph shows the beak sizes of the entire finch population studied by the Grants in 1976. The right graph shows the beak sizes of the survivors in 1978. In just 2 years, the mean beak size increased from about 9 mm to just above 10 mm.Review
Explore MoreThe Galapagos finches remain one of our world's greatest examples of adaptive radiation. Watch as these evolutionary biologists detail their 40-year project to document the evolution of these famous finches: Attributions
Which of the following are lines of evidence that support the theory of evolution by natural selection quizlet?What are the three lines of evidence that support the theory of evolution? Evidence from the fossil record, comparative anatomy, and DNA molecules support the theory of evolution.
Which of the following is evidence that supports the theory of evolution by natural selection?Darwin used multiple lines of evidence to support his theory of evolution by natural selection -- fossil evidence, biogeographical evidence, and anatomical evidence.
What are the 5 lines of evidence for evolution by natural selection?Evolution leaves observable signs. There are five lines of evidence that support evolution: the fossil record, biogeography, comparative anatomy, comparative embryology, and molecular biology.
What are the 4 evidences that support the theory of evolution?Evidence for evolution: anatomy, molecular biology, biogeography, fossils, & direct observation.
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