Charles Darwin's Theory Evolution and Natural Selection
In 1973, an evolutionary biologist named Theodosius Dobzhansky wrote an essay stating that "Nothing in biology makes sense except in the light of evolution." This has become a popular quote amongst biology educators, as it neatly summarizes the importance and beauty of Charles Darwin's theory. This unit provides an opportunity for the deft instructor to tie together the wide array of molecular-level concepts that typically precedes this unit with the macro-level concepts that follow it. Students with a true understanding of the concepts of evolution will gain an overall better understanding of all biological concepts, structures, and processes.
Essential concepts: Evolution, natural selection, behavioral adaptation, evolution, artificial selection, creationism, fossils, stratum, paleontology, speciation, extinction, catastrophism, gradualism, acquired trait, Lamarck,
Darwin, beagle, Galapagos Islands, origin of species, descent with modification, homologous structures, comparative embryology, vestigial organs, convergent evolution, analogous structures, biogeography, Pangaea, transitional forms, geographic separation, sexual selection, prezygotic, postzygotic Theory of Evolution (video)Population Genetics Project
Given the burgeoning success of flying hamster research and our fascination with the little rodents, you and I have decided to do our senior research thesis in Adrian's lab. A lot of the other researchers in Adrian's lab are focused on studying the genetics and molecular and biological function of specific genes and proteins in the flying hamsters. I think it would be interesting to study the genetics of an entire population of hamsters rather than studying just a single gene. The study of genetic variation within a population is called population genetics. Since we seem to be working together so well, let's go ahead and collaborate on our population genetics projects. Let's think about the mechanism of evolution before we get started, which begs the question: what is evolution? For now, let's think about evolution as a change in a characteristic within a population over time. As we learn more about population genetics, we'll be able to further refine this definition. Theory of Acquired Characteristics
The evolution of longer necks in giraffes is an example of Lamarckian inheritance. While having lunch with some other students in our building, we learn about their theories regarding the evolution of traits. The tell us they believe that the evolution of new anatomical factors are driven by necessity. Similarly, if an organism doesn't need a structure, that structure will become smaller and less developed because of disuse. The idea that characteristics an organism acquires during its lifetime can be passed on to its offspring is attributed to the scientist Jean-Baptiste Lamarck. This theory is called heritability of acquired characteristics or Lamarckian inheritance. Under this theory, a giraffe that stretches its neck to reach leaves in higher branches of trees would pass on stronger necks to its offspring, which would enable longer reach and eventually result in the evolution of giraffes with longer necks. Similarly, the theory proposes that the disuse of the small toe in mammals, such as pigs, caused it to disappear over time. We might say that the theory of acquired inheritance is akin to the adage Necessity is the mother of invention. The need for a trait drives the evolution of that trait. Principles of Darwinian Evolution Now, our classmates' theory seems pretty logical, but it's also a good idea to consider alternative possibilities. From our previous experiments, we know that variation exists within a population. Mutations can introduce new alleles, which might or might not give improved functionality as compared to the preexisting ones. Random assortment and crossing over create new combinations of alleles of different genes. For a given situation, new combinations of a gene could provide a competitive advantage for individuals of a population. Let's consider an example: suppose there are variations in size and strength of wings within an island hamster population. Hamsters with stronger, larger wings can fly farther than hamsters with smaller wings. However, since food and mates are plentiful on the island, the difference isn't really that important. Now, suppose the giant volcano on that island erupts, and the flying hamster habitat is completely destroyed. The hamsters with larger wings are strong enough to make it to a new islands, while the weaker ones are stuck on the ruined island or simply can't make it all the way to the other island. In the end, the significant alteration to the environment resulted in hamsters with larger, stronger wings. These are the basic principles of the theory of evolution that was proposed by Charles Darwin. He reasoned that populations rather than individuals evolved. This evolution is possible because genetic variation already exists within a population. Individuals with different genotypes in the population survive and reproduce at different rates. The agent that determines a differential rate of reproduction is called natural selection. Lamarckism vs. Darwinism Note the difference between Darwin's and Lamarck's theories. Lamarck believed that the need for a new trait would promote the evolution of that trait. Darwin proposed that evolution occurred through the selective pressure for a preexisting trait in a population. Both theories seem kind of reasonable, so how do we determine which theory most accurately describes what is going on in nature? Well, what if we tied the wings of flying hamsters so they can't fly? The theory of acquired characteristics predicts that the wings would shrink, since they aren't being used, and possibly disappear over the course of several generations. As it turns out, a scientist known as August Weismann conducted a similar experiment to disprove Lamarck's theory. Weismann repeatedly cut off the tails of mice over several generations. He found that the tails of mice in subsequent generations neither disappeared nor grew appreciably shorter. Today, Darwin's theory of evolution is widely accepted as the principle which governs population genetics. As we begin our study of flying hamster population genetics, we will see how Darwinian evolution can be used to predict the allelic, genotypic and phenotypic frequency within a population. |
Charles Darwin, Evolution, and Natural Selection Powerpoint LectureThe theory of evolution was not solely the result of Charles Darwin's work. This lecture begins by exploring the research of scientists like Cuvier, Hutton, Lyell, and Lamarck, as the pieces of evidence for natural selection began to fall into place. Finally, Charles Darwin embarks on his famous voyage on the H.M.S. Beagle, making discoveries that would lead to the eventual publishing of his book, On the Origin of Species. Each of Darwin's key observations, inferences, and conclusions used to construct this theory are explained. Examples of natural selection are given, ranging from pond guppies to the AIDS
virus. Finally, students will learn about the specific pieces of evidence used to support the theory: fossils, embryology, molecular homologies, and homologous structures Charles Darwin, Evolution, and Natural Selection Lecture Notes OutlineTaking efficient notes can be a big challenge for many students, especially when working from a Powerpoint lecture. This outline gives students a means to take notes that guides them toward important concepts and avoids the pitfalls of writing word-for-word or simply not taking notes at all. The outline is written as a series of questions, fill-in-the-blanks, or diagrams
Evidence of Evolution WorksheetsThe evidence of evolution worksheet set is a series of diagrams and short activities to illustrate each of the major types of discoveries that support evolutionary theory. The first evidence of evolution students will identify involves changes in skull and foot fossils of different ancestors of the modern horse. The next pieces of evidence compares embryos of different stages of chicken, human, fish, turtle, salamander, and rabbit. The common bones within the limbs of humans, whales, crocodiles, cats, birds, and bats will be identified as an example of homologous structures. Finally, the amino acid sequence of a portion of the cytochrome C protein molecule will be compared for several different species. Overall, these worksheets should give students an excellent overview of the major pieces of evidence that used to develop the theory of evolution
Evidence of Human Evolution
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