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Descent with modification One of the key words of our modern time is Evolution Outline u u u u u 1. Key concepts 2. Darwin developed the theory of evolution based on his observations and other evidence a. Darwin’s observations b. Factors that influenced Darwin’s thinking 3. Natural selection: A mechanism of evolution 4. More evidences 5. Key terms 6. Conclusions Key Concepts: Evolutionary theories gave early scholars new ways to interpret the occurrences in the world Today, biological evolution is interpreted as heritable changes Darwin and Wallace explained evolution on the basis of Natural Selection The traits that characterize a population can change over time Lamarck’ Lamarck’s Theory of Evolution Lamarck Theory of Inheritance of Acquired Characteristic Early Beliefs, and New Discoveries Aristotle – believed that each kind of organism was distinct from all the rest Linnaeus (classification) Hutton (gradual geologic change) Lamarck (species can change) Malthus (population limits) Cuvier (fossils, extinction) Lyell (modern geology) Darwin (evolution, natural selection) Mendel (inheritance) American Revolution 1750 Wallace (evolution, natural selection) French Revolution U.S. Civil War 1800 1850 1900 1795 Hutton proposes his theory of gradualism. 1798 Malthus publishes “Essay on the Principle of Population.” 1809 Lamarck publishes his theory of evolution. 1830 Lyell publishes Principles of Geology. 1831–1836 Darwin travels around the world on HMS Beagle. 1837 Darwin begins his notebooks on the origin of species. 1844 Darwin writes his essay on the origin of species. 1858 Wallace sends his theory to Darwin. 1859 The Origin of Species is published. 1865 Mendel publishes inheritance papers. Charles Darwin [1809-1882] called evolution “Descent with modification” Darwin - Voyage of the Beagle - 1831 At age 22, Charles Darwin began a five-year, round-the-world voyage aboard the Beagle He collected and examined the species that inhabited the regions the ship visited EQUATOR Galapagos Islands Darwin’ Darwin’s observations Prevailing ideas about species: they did not change or interbreed Darwin’s evidence for change came from: 1. his observations of living organisms 2. geologic evidence and fossil record 3. theories of population growth Darwin’ Darwin’s Mechanism of Evolution by Natural Selection Darwin’s Mechanism of Evolution by Natural Selection consists of observations on four aspects of the natural world: 1. Variation: Variation among individuals means they individually have different ability to obtain resources. 2. Overproduction: The reproductive ability of each species has the potential to cause its population increase. 3. Limits on population growth: Limited resources in the environment produces a struggle for existence 4. Differential Reproductive Success: Selection pressures act upon individuals that compete for resources, producing differential reproductive success Individuals that have difficulty producing members of the next generation have their genes reduced and possibly lost from subsequent populations Darwin’ Darwin’s Theory Takes Form Armadillo – 10 pounds Glyptodont – fossil from S. A. (2 tons!) Galapagos Islands today An example of natural selection: Darwin’ Darwin’s finches Factors that influenced Darwin’ Darwin’s thinking • • Geology: as Earth changed, so did types of fossil organisms in rock strata Population studies: many organisms are produced; only a few survive to reproduce [Thomas Malthus (1766-1834) Essay on Disease, Famine, and Population Size] • Artificial breeding experiments: humans “select” desirable traits in plants and animals; so does “nature” Artificial Selection In the process of artificial selection Humans have modified other species over many generations by selecting and breeding individuals that possess desired traits Terminal bud Lateral buds Brussels sprouts Cabbage Flower cluster Leaves Cauliflower Kale Flower and stems Broccoli Stem Kohlrabi Wild mustard Artificial Selection in Pigeons WILD ROCK DOVE Darwin used pigeons to explain connections between evolution and variation in traits Natural selection: A mechanism of evolution Darwin’s explanation for species diversity: Nature “selects” organisms which have inheritable traits (adaptations) suited to their environment which allow them to survive to reproductive age Survivors then breed and pass on these characteristics to their offspring Natural Selection Selection can increase the frequency of a trait in a population Environment may favor a trait over another Alfred Wallace Developed same theory as Darwin The Origin of Species 1859 - Darwin Evidence for the Theory of Evolution The Origin of Species Darwin made two major points in his book He presented evidence that the many species of organisms presently inhabiting the Earth are descendants of ancestral species He proposed a mechanism for the evolutionary process, natural selection Descendents of these ancestors accumulated diverse modifications or adaptations that fit them to specific ways of life and habitats. Fossils The study of fossils Helped to lay the groundwork for Darwin’s ideas Fossils are remains or traces of organisms from the past Usually found in sedimentary rock, which appears in layers or strata A sycamore leaf dropped 50 mya Tree fern dated 250 mya Barosaurus • This evolutionary tree of the elephant family is based on evidence from fossils. Homology Homology Is similarity resulting from common ancestry Anatomical Homologies Homologous structures between organisms Are anatomical resemblances that represent variations on a structural theme that was present in a common ancestor Human Cat Whale Bat Figure 22.14 Comparative embryology Reveals additional anatomical homologies not visible in adult organisms Pharyngeal pouches Post-anal tail Chick embryo Figure 22.15 Human embryo Evidence From Comparative Embryology Vestigial organs Are some of the most intriguing homologous structures Are remnants of structures that served important functions in the organism’s ancestors Molecular Homologies Biologists also observe homologies among organisms at the molecular level Such as genes that are shared among organisms inherited from a common ancestor Anatomical resemblances among species Are generally reflected in their molecules, their genes, and their gene products Species Percent of Amino Acids That Are Identical to the Amino Acids in a Human Hemoglobin Polypeptide 100% Human Rhesus monkey 95% Mouse 87% Chicken 69% Frog Figure 22.16 Lamprey 54% 14% The Evolution of DrugDrug-Resistant HIV Scientists designed the drug 3TC to interfere with reverse transcriptase, the enzyme that HIV uses to copy its RNA genome into the DNA of the host cell. Because 3TC is similar in shape to the cytosine nucleotide of DNA, HIV’s reverse transcriptase incorporates 3TC into its growing DNA chain instead of cytosine. This error terminates elongation of DNA and thus prevents HIV reproduction. 3TC-resistant varieties of HIV have a form of reverse transcriptase that can discriminate between cytosine and 3TC. These viruses have no advantage in the absence of 3TC. In fact, they replicate more slowly than viruses with normal reverse transcriptase. Once 3TC is added to their environment, it becomes a powerful selective agent, favoring reproduction of resistant individuals. Darwin’s main ideas can be summarized in three points. 1. Natural selection is differential success in reproduction (unequal ability of individuals to survive and reproduce). 2. Natural selection occurs through an interaction between the environment and the variability inherent among the individual organisms making up a population. 3. The product of natural selection is the adaptation of populations of organisms to their environment. Evolution Natural selection Fossils Descent with modification Artificial selection Homology Vestigial organs In Conclusion The Theory of Evolution by Natural Selection states More offspring are produces than the environment can support Variant forms of a trait may be more or less adaptive under environmental conditions An adaptive trait allowed organisms to survive and reproduce more frequently. The frequency of that adaptive trait increases in a population In Conclusion Comparative anatomy, biogeography, embryology, fossils, and a lot of other evidence showed changes in lines of descent Natural Selection results in modification of traits and can bring about the evolution of a new species