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Transcript
Chapter 15: The Origin of Life Abiogenesis: spontaneous generation; was generally believed as the way that new life formed... ...when actually BIOGENESIS was proven using the scientific method by (among others) * Francesco REDI- (17th century) "Does life really arise from rotting meat?" * Louis PASTEUR- (19th century) "Does life arise from materials in the air?" Biogenesis shows that life comes from pre-existing life, but does NOT explain where the first life came from. What is the Origin of Life on Earth??? There are Many Theories... Some of the thoughts: Special Creation ("God") Extraterrestrial Origins, or "Panspermia" (life came from OUTER SPACE). Evidence of organic compounds HAS been found in recovered meteorites. Chemosynthesis (chemical reactions occurred here on the young earth that resulted in organic compounds forming and then cells from these). This is by far the most popular scientific theory and probably the best-supported. One of the strongest hypotheses is "Chemosynthesis", or chemical evolution of the first cells on the planet earth, put forth by Alexander Oparin (early 1900's) Young earth ---> (1) volatile atmospheric gases (H2, H2O, CH4, NH3...) (NO O2), (2) warm seas, (3) energy from volcanoes, lightening, UV 1+2+3= MAYBE the first organic compounds formed as a result of this chemical reaction, much like in a test tube! When the seas washed onto shore and the puddles evaporated, the organic molecules were condensed into "packets" which were able to sustain themselves; "cells" This idea was NOT popular in the scientific community; it sounds an awful lot like spontaneous generation! Until... ...the experiment was tried out in a lab by Stanley Miller and Harold Urey (1953) who were NOT able to make cells, but did manage to cook up some organic molecules necessary for cells (amino acids, nucleotides, ATP) (Since then, modification of this experiment have been explored and some labs (See Sydney Fox) have been able to come up with some self-sustaining cell-like things (protocells, coacervates, microspheres)...who knows? If given a billion years or so...???) Formation of Earth: * * * Solar system estimated to be approximately 5 byo -This swirling mass of gas/dust collapsed inward (=sun) -Planets formed from violent collisions of space debris Estimated Age of earth about 4.6+ byo 1st life forms found to be ~3.5+ byo, primitive prokaryotic cells Scientific Evidence (Dating Methods): * The lineage of organisms (fossils) can be traced down through layers of rock of different ages (Lowest = Oldest). * Radiometric analysis: ages can be determined using elements in the rock- radioactive isotopes like 14C, 40K, 238U. -Radioactive isotopes have unstable nuclei that break down, give off radiation, and form new elements -Ex: C 12C (1/2 life is 5730 years) 40 K 40Ar (1/2 life is 1.3 billion years) 14 Living organism: Mollusk is absorbing 12C and 14C from the environment. The Ratio of 14C and 12C is the same. Dead organism: Once the mollusk dies, it no longer absorbs carbon. The radioactive 14C begins to decay and the amount of 14C in the mollusk shell decreases, while the amount of 12C remains the same. History: Because half of the 14C decays every 5730 years, the mollusk fossil's age can be determined by finding the ratio of 14C to 12C in the fossil and comparing it with the ratio in living organisms. -Ex: It is determined that a fossil contains of 98 grams of 12 C. The amount of 14C is determined to be 6.125 grams. How old is the sample? First, determine how many times the sample was reduced by 1/2: 98/2 = 49 49/2 = 24.5 24.5/2 = 12.25 12.25/2 = 6.125 = 4 half lives Second, look up the half-life of 14C (5730). Third, multiply the half-life by the number of half-lives that you calculated to have occurred. 5730 x 4 = 22,920 From Molecules to Cell-like structures: Sydney Fox – studies formation of 1st cells Microspheres: spherical & composed of protein molecules Coacervated: collection of droplets that are composed of molecules of nucleic acids and sugars -These can spontaneously form under certain conditions -Indicated that important aspects of cellular life can arise w/out direction from genes (ex. RNA can act as an enzyme) 1st life form -> prokaryotes: unicellular, simple, anaerobic, heterotrophic competition ensued... ---> chemotrophic autotrophs, unicellular, simple, anaerobic (Archaebacteria) ---> photosynthetic autotrophs, unicellular, simple, anaerobic brought about changes on earth...helped to add oxygen to the air... ...atmosphere forming, cloud cover, ozone (protection) ---> first eukaryotes...unicellular, about 1.5 bya; membrane-bound nucleus and organelles..."endosymbiont hypothesis" -->first multicellular organisms about 750 million yrs ago (fossils) fairly "recent"! Chapter 16: Evolution Early Evolutionary Theory Evolution (the theory that living things have changed over the earth’s history) is NOT a new idea. One of the earliest systematic theories was that of Jean Baptiste de Lamarck. He proposed that organisms developed or lost features due to "use or disuse". This was called the Inheritance of Acquired Characteristics (1809). For example: if a giraffe stretches its neck to reach higher branches in trees, will its offspring have longer necks as a result? Charles Darwin * as a young man, Englishman Charles Darwin served as a naturalist on the British naval vessel the HMS Beagle * he observed and collected specimens and fossils through parts on S. America and the S. Pacific (1831-36) * he read books on 1: geologic time (Sir Charles Lyell) and was aware that landforms and habitats change over time and that the earth was very old 2: populations (Thomas Malthus) which proposed that populations do not grow unchecked. There is limited space, food, & resources so there is a struggle for existence. The Galapagos Islands- off the coast of Ecuador; relatively "young" islands, formed largely from volcanic activity. They became inhabited with organisms from the mainland, but Darwin observed that each organism had evolved different features to adapt to the different island habitats until they had become separate, yet similar species. examples: 13 different species of finches, 14 different species of tortoises, etc. * Darwin returned to England to think about it for a while. * Many years later, he published his theory of evolution in a book called "...On the Origin of Species" (1859) * It should be noted that others, like Alfred Russel Wallace, had come up with this idea as well, but were as reluctant as Darwin to publish due to the political and religious themes of the day. Darwin realized that the earth is VERY old and has a long history of changes. This allows for: 1. VARIATION: Variation is the raw material for natural selection. Genetic (allele) variation is good! An inherited variation that increases an organism's chance of survival in a particular environment = an "adaptation". Adaptations that suit an organism in one environment may not be advantageous in another; and environment and habitats change, so must the organisms- - -> this may lead to new species over time. 2. COMPETITION: Living things face a constant struggle for existence. Predators, food, water are all limited. More organisms are born than can survive = competition; this sets up the so-called "survival of the fittest". 3. SELECTION: Organisms with that survive (and have favorable variations) will reproduce at a higher rate = "natural selection". This carries over their genes to another generation. Over successive generations, this tends to make a population better suited to its environment. Those are the three main points in his book. Patterns of Evolution 1. Divergent evolution: when isolated populations of a species evolve independently (ex: red fox/kit fox or even dogs) -usually occurs when geographic barriers separate members of a population -also occurs when a small group leaves an original population to colonize a new area -Adaptive Radiation: the evolution of many diversely adapted species from one common ancestor -Example: Darwin’s Finches Each species evolved from the original ancestor but as they traveled to different islands they had to adapt to the surroundings. 2. Convergent Evolution: unrelated species become more and more similar in features due to adaptation to similar environments (ex: cacti/euphorbs) 3. Coevolution: the joint change in two or more species in close interactions. As one changes, it forces the other to adapt to it. ex: flowers/ pollinators Evidence for Evolution There is quite a bit of scientific evidence that things began as simple cells and later changed into a variety of complex organisms which, have themselves changed over time. Some new species develop while others become extinct, but all can be traced back to a common ancestor. * Evolution is the theory that new species form when populations break off and develop traits that are different (new species). We can be traced back to a common ancestor. * Species change largely due to random changes (mutations) in their genes that occurs over a period of time. * In general, genetic changes that translate into some type of physical trait which give an organism an advantage are passed on to future generations, while those genes that put an organism at a disadvantage will probably not survive. * Which traits are favored, of course, depends upon the environment in which a species lives. Evidence from Fossils: The lineage of organisms can be traced down through layers of rock of different ages. Organisms leave behind FOSSILS or molds, casts or imprints in various strata of the earth. Ages can be determined using elements in the rock- radioactive isotopes like 14C, 40K, 238U Evidence from Living Organisms: 1. Similar Physical features = Common Ancestry: It LOOKS like several "new" species may evolve from one original species, mainly because of geographic separation (called allopatric speciation). example: Hawaiian Honeycreepers- birds that are different enough to have become separate species but have marked physiological similarities to one another. This would suggest they all started out as the same species, but diverged over time as they adapted to different islands. 2. Homologous Structures: Why do a bird wing, a human arm, a dog foreleg and even a whale's flipper all have the same bones in them? They all have different uses, but the same underlying physiology (radius, ulna, humerus, phalanges, etc.). This could mean that they evolved from the same common ancestor. Refer to Fig. 15-7 on pg. 289 of the text. 3. Vestigial Organs: Why do we have structures that we seem to have no use for? Like a tail bone (coccyx)? Our appendix? Ear muscles? Even whales have finger bones in their flippers. Some snakes have pelvic bones, but no legs attached? What's behind these??? MAYBE these "left-overs" point to our relationship to organisms that actually use these structures. 4. Embryological Development: Related organisms tend to have embryos that resemble one another and develop similarly. Refer to Fig. 15-9 on pg. 291 of the text. 5. Molecular Biochemistry: Analyses of the amino acid sequences or DNA of some organisms reveals similarities or differences between them. These can be utilized to determine relatedness. Chapter 17: Evolution and Speciation A "species" is a group of like organisms that are capable of reproducing viable offspring in nature. * Morphological species: based on similarities/differences in structure; easy to observe * Biological species: can interbreed Variation of Traits in a Population Population: all the members of the same species that live in a particular location at the same time and have the potential to interbreed. Members of a population, even though of the same species, are somewhat different genetically. * * * mutations in DNA recombination of genes during meiosis random fusion of gametes A difference in genotype usually results in a difference in phenotype Often, variation in traits are due also to environmental factors as well Example: Why are some of the perch in a pond bigger/longer than others? Bell Curve: Allele Frequencies and Genetic Equilibrium: Population Genetics Variations in genotype arise through mutation, recombination and crossing-over Gene Pool: the collection of genes for all the traits in a population (contains all the alleles for all the genes) Allele Frequency: the percentage of a specific allele of a gene in the gene pool A population in which allele frequencies do not change from one generation to the next is said to be in Genetic Equilibrium To maintain genetic equilibrium, several conditions must be met: -no mutations -no migrations -large populations -random mating -no selection of alleles (no natural selection) DISRUPTION OF GENETIC EQUILIBRIUM When gene frequencies change over time (Hardy-Weinberg does NOT hold true) then EVOLUTION happens. Factors that cause change in gene pools: 1. Mutation 2. Migration 3. Genetic Drift: allele frequencies in a population change as a result of random events or chance 4. Natural Selection: some alleles are more favorable to have than others TYPES OF NATURAL SELECTION Stabilizing Selection: selection that favors the most common variation Directional Selection: a shift in the bell curve one way or the other Disruptive Selection: selection that does not favor the most common variation of the trait w/in the poplulation Sexual Selection: mate preferences based on traits, usually some physical feature FORMATION OF SPECIES Speciation: the evolution of one or more species from a single ancestor species -when a species has been geographically separated and over time no longer can reproduce Ch. 18: Classification of Living Organisms (Taxonomy) Taxonomy: the science of classifying or grouping organisms; based on their presumed natural relationship An estimated 10 million organisms live on the planet (only a small fraction of the number that have ever existed in the earth's history) but only around 10% have been classified Why classify? 1. organization for study purposes 2. common names may be misleading (ex: starfish, jellyfish, goldfish) 3. scientists need a universal naming system (like metrics) 4. shows relationships between organisms (evolutionary path) One of the earliest taxonomic systems was set up by Aristotle around 2,000 yrs ago, based on his limited observations of organisms. He divided creatures up into 2 groups (plants/animals). Carolus Linnaeus- a Swedish naturalist who set up a system of grouping organisms into hierarchal categories, outlined in his Systema Natura; gave everything Latin names for: NOTE: "Phylum" is often called "Division" in botany (plants)! “Species” is called a “Strain” in monera (bacteria)! WITHIN a species, there may also be BREEDS, RACES, or VARIETIES that show distinctive phenotypes. We still use this system today, based on objective observations of structure, habitat, ancestry, etc. These classification categories are still used, but modern taxonomists have added to and amended it somewhat now that we have technology that can show biochemical and genetic similarities = more quantitative evidence as to degree of relatedness. We can also divide Linnaeus’s categories even further, if needed: subspecies, superclass, supphylum, etc. Today, every living thing has a universal Latin name, known as binomial nomenclature (2-part name) genus, species. "Making Order out of Chaos" Systematics: organizes the tremendous diversity of living things in the context of evolution; kind of a "who's related to whom" system. Phylogenetic tree: is a family tree showing the evolutionary relationships thought to exist among groups of organisms (for example, see pg. 343, Fig. 18-3). Evidence used to classify organisms into such groupings: 1. 2. 3. 4. fossil records morphology (structure/forms in organisms) embryological patterns of development chromosomes and macromolecules Cladistics: a relatively new system of phylogenetic classification, using certain features of organisms called "shared derived characteristics" to establish relatedness. Cladogram (for example, see pg. 346, Fig. 18-6). THE SIX KINGDOM SYSTEM Kingdom Archaebacteria Eubacteria Protista Fungi Plantae Animalia Cell type prokaryotic prokaryotic eukaryotic eukaryotic eukaryotic eukaryotic Number of Cells unicellular unicellular mostly unicellular mostly multicellular multicellular multicellular Nutrition both (auto & heterotrophic) both both heterotrophic autotrophic heterotrophic