Darwin s Observations & Conclusions The Struggle for Existence 1
Voyage of the Beagle During His Travels, Darwin Made Numerous Observations And Collected Evidence That Led Him To Propose A Revolutionary Hypothesis About The Way Life Changes Over Time 2
Darwin s Observations Patterns of Diversity were shown Unique Adaptations in organisms Species Not Evenly Distributed Australia, Kangaroos, but No Rabbits S. America, Llamas 3
Darwin s Observations Both Living Organisms & Fossils collected Fossils included: Trilobites Giant Ground Sloth of South America This species NO longer existed. What had happened to them? 4
Evidence for Evolution The Fossil Record 5
Definition Evolution is the slow, gradual change in a population of organisms over time 6
Darwin s Observations Left unchecked, the number of organisms of each species will increase exponentially, generation to generation In nature, populations tend to remain stable in size Environmental resources are limited 7
Darwin s Conclusion Production of more individuals than can be supported by the environment leads to a struggle for existence among individuals Only a fraction of offspring survive each generation Survival of the Fittest 8
Darwin s Observations Individuals of a population vary extensively in their characteristics with no two individuals being exactly alike. Much of this variation between individuals is inheritable. 9
Darwin s Conclusion Individuals who inherit characteristics most fit for their environment are likely to leave more offspring than less fit individuals Called Natural Selection 10
Darwin s Theory of Evolution The unequal ability of individuals to survive and reproduce leads to a gradual change in a population, with favorable characteristics accumulating over generations (natural selection) New species evolve 11
Common Descent with Modification Darwin proposed that organisms descended from common ancestors Idea that organisms change with time, diverging from a common form Caused evolution of new species 12
Theory of Evolution Today Supporting Evidence 13
Homologous Structures 14
Evidence for Evolution - Comparative Embryology Similarities In Embryonic Development 15
Similarities in DNA Sequence 16
Evolution of pesticide resistance in response to selection 17
Evidence for Evolution Evolution Observed Evolution of drug-resistance in HIV 18
Evidence for Evolution Evolution Observed Selection against small guppies results in an increase in average size 19
Evolutionary Time Scales Macroevolution: Long time scale events that create and destroy species. 20
Evolutionary Time Scales Microevolution: Short time scale events (generation-togeneration) that change the genotypes and phenotypes of populations 21
Evidence of Evolution Key Concept Darwin Argued That Living Things Have Been Evolving On Earth For Millions of Years. Evidence For This Process Could Be Found In: The Fossil Record The Geographical Distribution of Living Species Homologous Structures of Living Organisms Similarities In Early Development 22
Fossil Record Earth is Billions of Years Old Fossils In Different Layers of Rock (sedimentary Rock Strata) Showed Evidence Of Gradual Change Over Time 23
Geographic Distribution of Living Species Different Animals On Different Continents But Similar Adaptations To Shared Environments 24
Homologous Body Structures Scientists Noticed Animals With Backbones (Vertebrates) Had Similar Bone Structure May Differ In Form or Function Limb Bones Develop In Similar Patterns Arms, Wings, Legs, Flippers 25
Homologous Body Structures Structures That Have Different Mature Forms But Develop From The Same Embryonic Tissues Strong Evidence That All Four-Limbed Animals With Backbones Descended, With Modification, From A Common Ancestor Help Scientist Group Animals 26
Homologous Body Structures 27
Homologous Body Structures Not All Serve Important Functions Vestigial Organs Appendix In Humans Legs On Skinks 28
Darwin s Theory of Evolution Organisms Change Over Time 29
Natural Selection Driving force for evolution During the struggle for resources, strongest survive & reproduce Idea that at least some of the differences between individuals, which impact their survival and fertility, are inheritable. 30
Natural Selection and Artificial Selection Natural Selection Differences Among Individuals Of A Species Artificial Selection Selective Breeding To Enhance Desired Traits Among Stock or Crops 31
Natural Selection and Artificial Selection Key Concept: In Artificial Selection, Nature Provided The Variation Among Different Organisms, And Humans Selected Those Variations That They Found Useful 32
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Origin of Species Concepts and Controversy 34
Evolution By Natural Selection Concepts The Struggle for Existence (compete for food, mates, space, water, etc.) Survival of the Fittest (strongest able to survive and reproduce) Descent with Modification (new species arise from common ancestor replacing less fit species) 35
Survival of the Fittest Fitness Ability of an Individual To Survive & Reproduce Adaptation Inherited Characteristic That Increases an Organisms Chance for Survival 36
Survival of the Fittest Adaptations Can Be: Physical Speed, Camouflage, Claws, Quills, etc. Behavioral Solitary, Herds, Packs, Activity, etc. 37
Survival of the Fittest Fitness Is Central To The Process Of Evolution Individuals With Low Fitness Die Produce Few Offspring Survival of the Fittest AKA Natural Selection 38
Key Concept Survival of the Fittest Over Time, Natural Selection Results In Changes In The Inherited Characteristics Of A Population. These Changes Increase A Species Fitness In Its Environment 39
Natural Selection Cannot Be Seen Directly It Can Only Be Observed As Changes In A Population Over Many Successive Generations Radiation Fossil Record 40
Descent With Modification Takes Place Over Long Periods of Time Natural Selection Can Be Observed As Changes In Body Structures Ecological Niches Habitats 41
Descent With Modification Species Today Look Different From Their Ancestors Each Living Species Has Descended With Changes From Other Species Over Time 42
Descent With Modification 43
Descent With Modification Implies All Living Organisms Are Related Single Tree of Life DNA, Body Structures, Energy Sources Common Descent All Species, Living & Extinct, Were Derived From Common Ancestors 44
IV. Evolution of Populations A. Populations are the smallest unit that can evolve (adapt) B. Variation exists in a population 1. Due to resources- food, soil 2. Due to heredity- genotype C. Cause of variation in Genotypes 1. Mutation 2. Recombination (independent assortment, crossing-over) 3. Random fusion of gametes
IV. Evolution of Populations D. Gene Pool 1. All genetic information in a population 2. Frequency of a certain allele in a population will determine the phenotype frequency E. Hardy-Weinberg Equilibrium 1. Allele frequencies stay the same in an undisturbed population (genetic equilibrium) 2. Allows scientists to measure changes in a gene pool
V. Disruption of Genetic Equilibrium A. Mutation 1. Caused by mutagens 2. Change DNA producing totally new alleles 3. Most are harmful B. Migration 1. Immigration and emigration of individuals 2. Ensures gene flow
V. Disruption of Genetic Equilibrium C. Genetic Drift 1. Change of allele frequencies due to random events 2. Small populations are highly affected D. Nonrandom Mating 1. Geographic proximity 2. Assortive matinglike to like
V. Disruption of Genetic Equilibrium E. Natural Selection 1. Most significant factor in evolution of populations 2. Nature selects against non-fit individuals 3. Reduces harmful alleles
V. Disruption of Genetic Equilibrium 4. Types a) Stabilizing Selection- towards the average b) Directional Selection- towards one extreme c) Disruptive Selection- away from the average d) Sexual Selection- females tend to choose