Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Evolution Introduction Charles Darwin Born in England in 1809 Enrolled in divinity school at Cambridge; graduated in 1831 In 1831, Darwin signed on the naturalist on the HMS Beagle & traveled around the world for the next 5 years He gathered data during his travel; that data was used as the basis for his books and ideas on evolution Bozeman Biology: Evolution (9.22 min.) Evolution Defined The change that has occurred in a species of organism with the passage of time. The passage of time is used here to mean from the distant past to the present. Diversity of living things is a direct result of biological evolution. Traits in species and organisms developed overtime by evolution. Evolution unifies all the different areas of study of biology. Fossil Evidence for Evolution Fossils are the remains of organisms that lived in the distant past. Countless organisms have lived and died since life began; many left behind remains. Examining structures in a fossil species & comparing them to similar species today, evolution can be seen. Examples of fossils and their method of formation are hard parts, imprints, molds, petrifaction, refrigeration, amber and tar pits. Hard Parts Hard parts are bones, teeth, or shells of organisms that lived in the past. Hard parts often survive the natural process of decay. Evolution is change, for example fossil skeletons of horses show how this organism has evolved from a small horse to the modern day large horse. Imprints Imprints are impressions made by plants and animals in soft soil or mud, that with the passage of time harden to become rock Example: dinosaur footprints & outlines of leaves in rocks Molds An organism suddenly dies in the ocean & sinks to the bottom becoming covered with mud, as it decays its outline remains, forming a mold of that organism The sand and mud harden to form rock, then millions of years later the rock can be opened to reveal the mold of that organism Petrifaction Minerals in water that covered trees and bones of organisms diffused into the cells of the organism, forming rock that resembles the organic tissue that was replaced Examples: petrified forests & petrified wood Refrigeration Occurs when an organism is preserved by cold temperatures or ice Mammoths have been found preserved in ice, in remarkably good condition Amber A form of fossilized resin from trees that lived millions of years ago As the resin dripped down from the tree, it often trapped and surrounded an insect or part of a plant As the resin hardened, the organism that was trapped inside was preserved Most amber comes from the Dominican Republic Amber is prized by jewelers for its gem-like quality & by scientists for any organism that might be trapped inside Tar Pits Accumulation of oil or asphalt that seeped up to the earth’s surface. Animals often became trapped in the sticky asphalt, resulting in the soft parts of the animal decayed, but the hard parts were preserved by the asphalt The La Brea tar pits in Los Angeles are famous for fossils of dire wolves, saber-toothed tigers, mammoths, horses, camels and other organisms Other tar pits have been found in Iran, Peru, Poland & Russia Dating of Fossils Two different techniques used to date fossils Relative dating & absolute dating Relative Dating Method used to determine the age of a fossil by comparing its location relative to fossils in nearby rock layers An exact age is not assigned to a fossil When a rock formation is examined, the oldest fossils are found in the bottom layer & the youngest are found in the top Some species of organisms were once found all over the world, but lived for a short time. Fossils of these organisms are called index fossils. Absolute Dating Method used to determine the approximate age of a fossil by relying on the radioactivity of certain elements & their half lives Half life is the amount of time that it takes for an element to decay into half of its original amount The older the fossil, the more the radioactive element has decayed Fossils of organisms that lived up to 50,000-70,000 years ago can be dated using Carbon-14 Sedimentary Rock Most fossils are found in sedimentary rock, which is formed by the deposition of very small particles of rock, clay or silt. It forms in layers, often in water & takes millions of years to form Igneous Rock Formed by volcanic activity & never contains fossils The high temperature associated with the formation of this rock incinerates any organism unfortunate enough to be caught in the lava flow Metamorphic Rock Formed by tremendous heat and pressure applied to igneous & sedimentary rock Fossils are not found in metamorphic rock Additional Evidence of Evolution A common ancestor is an individual from which 2 or more related species could have evolved With time, organisms change and diverge from their common ancestor to form new species Comparative Anatomy Anatomy is the body structure Evolutionary relationships based on comparative anatomy depend on homologous structures Homologous structures are similar in construction & evolutionary development but dissimilar in function Analogous structures are similar in function but dissimilar in construction & evolutionary development & are not used in comparative anatomy Vestigial structure at one time had a function in the evolutionary history of an organism but now does not have a function Comparative Embryology Similarity exists between vertebrate embryos As the embryos develop, they begin to acquire the unique characteristics of their species The similarity of embryological development supports the concept of the common ancestor Comparative Biochemistry DNA, RNA, the genetic code & protein synthesis are similar in all organisms The greater the genetic and molecular similarity between species, the closer the common ancestor Humans & chimpanzees have 98% of their genes in common Hemoglobin in humans is almost identical to hemoglobin in all other vertebrates. The similarity in chemical structure demonstrates that al vertebrates can be traced back to a common ancestor Theories of Evolution Naturalists tried to explain the changes they observed in the fossil record through the concepts of acquired characteristics and use and disuse In 1859, Charles Darwin published his view on evolution in his book On the Origin of Species He proposed the theory of natural selection Hugo De Vries ( early 1900’s) updated the theory of natural selection by suggesting that mutations are a source of variation in a population Natural Selection Natural selection explains how evolution takes place Overproduction: When members of a species reproduce, they produce more offspring than is necessary Struggle for survival: Overproduction results in competition for scarce resources such as food, water & territory Variation: Within every population, members of a species show variation (differences) in their traits Natural Selection continued Natural Selection: Nature selects those variations that are most fit. Organisms with the best variation survive the struggle for existence & reproduce & are then passed on to the next generation Formation of new species: The most fit variations become the norm within the population. The less fit variations are eliminated. Eventually, a new species of organism evolves, that is significantly changed from that of its ancestor. Natural Selection (10.16 min.) Mutation A source of variation in a population that can lead to the formation of new species with the passage of time Hugo De Vries noted sudden changes in the evening primrose, he called the changes mutations The Rate of Evolution Can be explained by gradualism & punctuated equilibrium Gradualism: evolution is a slow and gradual process that proceeds in numerous small steps, taking many years and generations for new species to form Punctuated equilibrium: biologists believe that evolutionary change occurs in sudden spurts during which many new species are formed, followed by long periods of stability with no speciation The Hardy-Weinberg Law Discovered by G.H. Hardy & W. Weinberg in 1908 It predicts how gene frequencies are maintained from one generation to the next This law states that in a population the frequency of an allele remains constant from generation to generation, as long as five conditions are met It can be stated in mathematical terms In order for the Hardy-Weinberg Law to work, these 5 conditions must be met The gene pool must be large to provide statistical accuracy of the Hardy-Weinberg Law No migrations can be allowed into or out of the population because this changes the frequency of alleles Mating must be random to ensure that the laws o probability work. The organisms decide who their mates are without restrictions or interference No mutations can occur because mutations can change the frequency of an allele within a population No natural selection can be present because it tends to favor individuals within the population that have more-fit alleles Geographic & Reproductive Isolation Geographic isolation is caused by geographical barriers such as mountains, deserts, oceans, and rivers It results in the physical separation of individuals within a population, preventing random mating between individuals Eventually, the organisms become reproductively isolated and are no longer able to mate and produce fertile offspring When that happens, two new species have developed Reproductive Isolation also occurs when species reproduce during different times of the year, have different mating rituals, or have reproductive structures that prevent mating between the male and female Environmental Factors They can favor one variation of a trait over another, resulting in a change in the frequency of an allele within a population The Origin of Life on Earth A.I. Oparin & J.B.S. Haldane proposed the heterotroph hypothesis to explain how the first cells might have originated on earth According to this hypothesis, the first cells on earth were heterotrophs and most likely originated in the ocean The Heterotroph Hypothesis A modern explanation states that the earth’s early atmosphere was a reducing atmosphere (one with little or no oxygen). Among the gases that were probably present were: water vapor, nitrogen, carbon monoxide, carbon dioxide, & some hydrogen UV radiation, high temperature & lightning were energy sources for chemical reactions between the gases These reactions may have resulted in the production of simple organic compounds such as simple sugars, amino acids, fatty acids, glycerol and nucleotides Complex Organic Compounds Took place in oceans Producing complex carbohydrates, proteins, lipids & nucleoproteins Compounds grouped together and formed the first primitive prokaryotic heterotrophic cells These early heterotrophs used organic compounds in the ocean as a source of energy, producing alcohol & carbon dioxide as waste products The first autotrophs were primitive prokaryotic cells They used carbon dioxide & water to produce glucose & oxygen by photosynthesis The early autotrophs introduced oxygen to the atmosphere Modern heterotrophs are eukaryotic & developed the ability to use oxygen for respiration Aerobic respiration produces more energy than anaerobic respiration As the saying goes; the rest is evolutionary history. Endosymbiotic theory Heterotrophic and autotrophic eukaryotic cells developed from a symbiotic relationship between prokaryotic organisms Prokaryotic organisms with the ability to produce energy from organic molecules were ingested by a larger prokaryote, were incorporated into the cell, then evolved to become the mitochondria of modern heterotrophs Other prokaryotic organisms with the ability of photosynthesis were ingested by a prokaryote and evolved into the chloroplasts of modern autotrophs The theory is supported by the fact that mitochondria and chloroplasts have their own DNA & reproduce independently of the cell by binary fission Eukaryotic cells reproduce by mitosis Mitochondria & chloroplasts have ribosomes that are similar to prokaryotic organisms