* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Ch 21 PP slides
Survey
Document related concepts
Natural selection wikipedia , lookup
Evidence of common descent wikipedia , lookup
Evolution of metal ions in biological systems wikipedia , lookup
Microbial cooperation wikipedia , lookup
Evolution of sexual reproduction wikipedia , lookup
Hologenome theory of evolution wikipedia , lookup
Inclusive fitness wikipedia , lookup
Symbiogenesis wikipedia , lookup
Organisms at high altitude wikipedia , lookup
Saltation (biology) wikipedia , lookup
State switching wikipedia , lookup
The eclipse of Darwinism wikipedia , lookup
Population genetics wikipedia , lookup
Transcript
Chapter 21 The Origin and Evolution of Life Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 1 Early Attempts at Understanding • Ancient cultures believed life could be generated from nonliving matter (spontaneous generation) • Later experimental evidence proved that life can only come from other living things (biogenesis) Francis Redi (1668) • Two jars with decaying meat, both exposed to atmosphere, one covered with gauze, one uncovered – Flies settled on meat in open jar – Maggots appeared on meat in open jar – Did not appear in covered jar • Conclusion: maggots came from the eggs of the flies 2 Louis Pasteur (1861) • Placed fermentable sugar solution in a flask with a swan neck Long swan neck open to air to allow oxygen to enter – Mixture and flask boiled to kill organisms in solution – Pasteur postulated: • Spontaneous generation would not occur even in the presence of O2 • Organisms in air caused fermentation • Organisms would settle on the bottom of the curved portion of the neck and not reach solution • Sugar solutions would not ferment • Also cut off swan neck flask – Microorganisms reached sugar solution – Solution fermented • Conclusion: spontaneous generation does not occur 3 Current Theories about the Origin of Life • Extraterrestrial Origin for Life on Earth – Life existed elsewhere in solar system (Mars) – Possibly arrived from extraterrestrial sources via meteorites • Earth Origin for Life on Earth – Early earth was probably a hot planet with no oxygen in the atmosphere – Organic molecules could have possibly: • Formed from inorganic ones • Collected in oceans • Then served as building blocks and a source of energy for simplest organisms – Life could have originated as: • Heterotroph • Autotroph 4 Heterotroph Hypothesis • Heterotrophs (animals, fungi, most protozoa, bacteria) – Consume organic molecules from surroundings in order to: • make new molecules • provide an energy source • First living things were bacteria-like anaerobic organisms that lived off organic molecules accumulated in ocean • As usable molecules were depleted from the environment, these primitive cells may have mutated to be able to convert unusable material to usable compounds • Genetic mutations may have been common – Amount of UV light high (no ozone to screen out UV) • Mutated organisms survived and reproduced • Through series of genetic mutations, complex series of biochemical reactions originated within some cells in order for 5 the cells to convert unusable to usable compounds Autotroph Hypothesis • Autotrophs – Use external energy to combine inorganic molecules into organic molecules • Chemoautotrophs – use energy from inorganic chemical reactions (some prokaryotic organisms) • Photoautotrophs – use energy the sun But in from reality, (eukaryotic plants, algae, some prokaryotic organisms) • First organism was a chemoautotroph that used WE JUST DON’T KNOW energy released from inorganic chemical reactions to synthesize organic molecules • Supporting Evidence – Most prokaryotic organisms are autotrophic and live in hot hostile environments (hot springs, thermal vents) • Could have originated on hotter earth • Subsequent evolution could have led to a variety of prokaryotic cells 6 The Origin of Genetic Material How genetic information could have been stored inside early life forms Both DNA and RNA store and transfer genetic information – RNA is a simpler molecule – In most cells today • DNA stores genetic information • RNA assists DNA in transferring genetic information • However, in some viruses, RNA serves as the genetic material • Evidence for RNA being the first genetic material: – RNA can be assembled from simpler subunits that could have been present on early earth – RNA molecules are able to make copies of themselves without the need of enzymes or being inside a cell – Once a genetic material can be copied, the organism can reproduce 7 Developing of the Earth’s Atmosphere • Initially earth was too hot to have an atmosphere • As it cooled, an atmosphere without oxygen formed • About 2 billion years ago, atmosphere changed to one with oxygen – Mainly as a result of photosynthesis • Living things existed before oxygen was present • First anaerobic organisms mutated to photosynthetic autotrophs • Waste product of photosynthesis is O2 – Aerobic respiration evolved resulting in more efficient conversion of food to energy – Ozone also formed resulting in: • Diminished spontaneous formation of complex organic molecules • Reduced genetic mutations in cells 8 Developing of the Earth’s Atmosphere 9 Establishment of Three Major Domains of Life 1. Eubacteria • Many different metabolic abilities Heterotrophs, photoautotrophs, chemoautotrophs Prokaryotic 2. Archaea • • • • Primarily chemoautotrophs Usually found in harsh environments Use inorganic chemicals to generate energy Reactions often produce methane (CH4) or hydrogen sulfide (H2S) 3. Eucarya • • • Plants, animals, fungi, protozoa, algae Cells are larger than that of the prokaryotics Cells appear to have incorporated cells of other organisms 10 From Prokaryotes to Eukaryotes The Endosymbiotic Theory • Eukaryotic cells came from combining several different types of prokaryotic cells – Some eukaryotic organelles may have originated as free-living prokaryotes – Cells formed a symbiotic relationship, • Adapted, reproduced as a team and evolved into present eukaryotic cells – Examples: mitochondria, chloroplasts 11 The Endosymbiotic Theory 12 Role of Natural Selection • Evolution – continuous genetic adaptation of a population of organisms to its environment over time – Involves changes in genes present in a population (not individual organisms) • Natural Selection - process that encourages passage of beneficial genes and discourages passage of harmful (or less valuable) genes to future generations • Theory of Natural Selection – (proposed by Darwin and Wallace) Individuals whose gene combinations favor life in their surroundings will be likely to survive and pass their genes on to the next generation • Theory of Evolution – populations of organisms become genetically adapted to there surroundings over time – Natural selection brings about evolution by selecting which genes are passed on Natural Selection Genetic selection Evolution 13 Misinterpretations Associated with Natural Selection • “Survival of the Fittest” – Survival alone is not good enough – Survival and reproduction is the key • Struggle for life – Not necessarily open conflict – But finding the necessary resources for survival and reproduction 14 Genetic Diversity influences the process of natural selection Resulting from mutation • Spontaneous mutation – changes in DNA that cannot be tied to any particular causative agent – Cosmic radiation, mutagenic chemicals – Naturally occurring genetic mutation rates are low (~1 in 100,000) • Possible outcomes when a gene is altered – Mutation so minor that it has no effect – Mutation harmful – Mutation is beneficial • In order for mutations to be passed to the next generation, they 15 must happen in cells that will become sex cells Genetic Diversity Resulting from sexual reproduction • Does not generate new genetic information • Genes recombine into new mixtures Genetic recombination: each individual has unique set of genes, half donated by mother, half by father Acquired characteristics do not influence natural selection not genetically determined gained during life of organism cannot be passed on to other generations 16 Processes that drive natural selection Selecting agents – specific environmental factors that favor and influence the likelihood that certain characteristics will be passed on • Differential Survival – Some individuals possess characteristics enabling them to preferentially survive and pass on their genes • Differential Reproductive Rates – Some organism may be able to better utilize resources to produce more offspring • Differential Mate Selection – Some individuals possess characteristics enabling them to be more frequently chosen as mates • Size, aggressiveness, attractiveness to opposite sex 17 Differential Reproductive Rates Cows act as the selecting agent by eating the taller plants first Two identical fields of clover Tall plants rarely reproduced Seeds from both fields were collected and grown under identical conditions Only short plants produced seeds Cows selectively ate plants with tall gene Seeds from grazed field produced mostly short plants Seeds from ungrazed field produced tall, short but mostly medium 18 sized plants Hardy-Weinberg Concept Conditions necessary for genetic makeup to remain constant 1. Mating must be completely random 2. Mutations must not occur 3. Migration of individual organisms into and out of the population must not occur 4. The population must be very large 5. All genes must have an equal chance of being passed onto the next generation (no natural selection) Concept allows for comparisons of genes within a population to determine if genetic changes are occurring of genes of two different populations to determine similarities in genetic makeup Concept is an argument for evolution because most of these conditions cannot be met 19 Processes That Drive Natural Selection All the genes of all individuals in a population Constant genetic makeup over several generations (unchanging gene pool) indicates that evolution is not taking place A changing gene pool indicates evolution 20 is taking place Evidence for the Theory of Evolution 1. Species and populations are changing genetically through mutations, adaptations, environmental changes, selective breeding, extinctions 2. Evolution occurs by small steps – – – All species use same DNA code and amino acid building blocks Difficult to eliminate a structure that becomes part of a process controlled by genes (example: appendix) Closely related species have similar DNA and embryological development 3. Fossil records show changes in kinds of organisms. – Species appear and subsequently become extinct 4. New techniques and discoveries support evolution 21 Misconceptions about the Theory of Evolution 1. Evolution happened only in the past – Lots of evidence exists for current genetic changes 2. Evolution has a specific goal – – Natural selection favors organisms that best fit the current environment Random events can have major influence on natural selection 3. Changes in environment cause mutations that are needed for an organism to survive – Mutation are random events (not necessarily adaptive) 4. Individual organisms evolve – Individuals may adapt by changing behavior or physiology but they cannot change their genes 5. An existing species may have arisen from another present-day species – The species in question may have had a common ancestor 22 Species • Population of organisms whose members have the potential to interbreed naturally to produce fertile offspring but do not interbreed with other groups – Populations that demonstrate gene flow between them • Gene flow - movement of genes from one generation to the next or from one region to another – Smallest irreversible step in the evolutionary process • Two key ideas in these definitions – Species is a population of organisms (not individuals) – Offspring must be fertile • Identifying species – Biological species concept • Species can be identified by their inability to interbreed • Not a practical way to distinguish species – Morphological species concept • Method of using physical characteristics to identify species • Useful but not foolproof 23 Speciation • Range – geographical area over which a species is found • Geographic isolation – portion of a species becomes reproductively isolated from the rest of the gene pool by geographic change – No gene flow occurring • Geographical barriers - geological features that keep portions of the species from exchanging genes • Speciation - process of generating new species – Over a long period of time, accumulated genetic differences may result in subspecies 24 How New Species Originate Three step process 1. 2. 3. • • Geographic isolation occurs Selective agents favor specific valuable genetic combinations Genetic differences become so great that reproduction between two groups is impossible – Populations become separate genetically Process has occurred only if gene flow between isolated populations does not occur even after barriers are removed Separation of species is not enough to generate new species 25 26 27 28 Theory of Natural Selection as a Mechanism for Evolution • • 1. 2. 3. 4. Proposed by Darwin and Wallace (1858) Based on the following assumptions All organism produce more offspring than can survive No two organisms are exactly alike Organisms are in a constant struggle for survival Individuals that possess favorable characteristics for their environment have higher rate of survival and produce more offspring 5. Favorable characteristics become more common in the species and unfavorable characteristics are lost 29 30 End of Chapter 21 31