Introduction to Evolution (Pre-evolution)

INTRO TO EVOLUTION Evolution: All species are descendants of ancient species that were different from modern day species ●​ Change in inherited characteristics of populations over time PRE-EVOLUTION THEORIES 1. The world was less than 10 000 years old and relatively unchanging 2. Species were fixed and do not change over time from generation to generation UNIFORMITARIANISM ●​ James Hutton was one of the first to challenge the notion of Earth’s young age ○​ Studied erosion and sedimentation - takes millions of years to form current landscapes ●​ Uniformitarianism: Earth was formed entirely by the slow-moving processes of erosion and sedimentation FOSSIL RECORDS ●​ Skeletons of elephants and mammoths were compared and similarities were found by Georges Cuiver ●​ Concluded that they were different enough to be different species but of common ancestry LAMARCK’S THEORY OF ADAPTATION ●​ Species change over time due to adaptation to their environment through newly acquired traits ○​ Change in their lifetime ○​ Transmit acquired characteristics to the next generation ●​ Three guiding ideas on why species change: 1.​ Use & Disuse: Gaining/losing characteristics based on what is used by an organism 2.​ Acquired characteristics would pass on to offspring 3.​ Perfection with Use & Need: Organisms strive for perfection in order to maximize their success ●​ Flaws: ○​ Organisms cannot inherit characteristics that their predecessors acquired ○​ Characteristics inherited must be encoded in parental DNA and passed onto offspring ●​ Truths: ○​ Adaptation: Inherited characteristic that improves an organism’s survival in an environment DARWIN’S PATTERNS OF DIVERSITY Evolution: Change in inherited characteristics of populations over time Patterns of Diversity: 1.​ Species vary globally: ●​ Distantly related species living in similar environments are similar physically and behaviorally ●​ Unique organisms are found in unique environments 2.​ Species vary locally: ●​ Related animal species that occupy different habitats had different features 3.​ Species vary over time: ●​ Species living today are descended from ancestral species THOMAS MALTHUS’ THEORY OF COMPETITION ●​ Human population is growing at a faster rate than the rate at which supplies of food and other resources can be produced ●​ Resources are limited meaning that only certain individuals in a population can service DARWIN’S THEORY OF EVOLUTION TWO MAJOR POINTS 1.​ All species of organisms living on Earth today are descended from ancestral species 2.​ The mechanism that causes species to change over time is natural selection ORIGIN OF SPECIES All Organisms are Descended from Others: ●​ Proposed the major concept of descent with modification ○​ Descendants of the earliest organisms spread into various habitats over millions of years and accumulate different modifications/adaptation ●​ Explains the diversity of life Survival of the Fittest - Natural Selection ●​ Adaptations that enable organisms to survive and reproduce in its environment ●​ 3 observations: Struggle for existence, variation, the environment NATURAL SELECTION 1. Struggle for Existence ●​ More offspring than there are resources in nature ●​ Only a small percentage of offspring survive every generation 2. Variation ●​ Differences among members of the same species ●​ A certain variation may be best suited to a specific environment ●​ Individuals with this heritable variation are more likely to produce the most offspring ●​ This variation becomes more common 3. Role of the Environment ●​ As the environment changes, species adapt or go extinct ●​ The environment selects individuals in a species with variations that are best suited to it SURVIVAL OF THE FITTEST ●​ Fitness: An individual’s ability to survive and reproduce in a specific environment ●​ Survival of the Fittest: Individuals with increased fitness will survive/reproduce more successfully ●​ Natural selection selection does not make organisms ‘better’; an adaptation might work well in one environment but not so well in another EVIDENCE FOR EVOLUTION 1. FOSSIL RECORDS ●​ Fossil: Any preserved remains, impression, or trace of an organism from the past. ○​ Fossils within layers show that a succession of organisms have populated Earth throughout a period of time ●​ Fossil record: Chronological collection of life’s remains in rock layers, recorded throughout time. ●​ Paleontologists rely on transitional fossils to show a possible link between two or more organisms. ●​ Fossil records can also provide evidence for the extinction of species ●​ Fossils records (and thus evolutionary history) are limited for species that do not possess bones, shells or exoskeletons. 2. GEOGRAPHIC DISTRIBUTION ●​ The differences and similarities between organisms in different parts of the world suggest that today’s organisms evolved from ancestral forms ●​ Idea that similar habitats (even if they are on opposite sides of the world) select for similar adaptations 3. COMPARATIVE ANATOMY ●​ Homologous features: Structures that share a common origin/ancestry but may serve different functions in modern species ○​ Structures that originally functioned in one way in ancestral species become modified as they take on new functions. ○​ In other words, it doesn’t make sense to make a bat’s wing out of a whale’s flipper unless… they shared a common ancestor! ●​ Vestigial structures: type of homologous structure that might have had function in an ancestral species but no clear function in some of their modern descendants. ○​ Usually smaller in modern descendants. ○​ Natural selection would favour the survival and reproduction of individuals that possess reduced vestigial structures. ●​ Analogous features: Structures similar in function but not in origin or anatomical structure ○​ Does not support the idea of common ancestry but it does show that certain adaptations are suited to certain environment 4. COMPARATIVE DEVELOPMENT ●​ Similar embryological development in closely related species ●​ Embryos of closely related organisms often have similar stages of development 5. MOLECULAR BIOLOGY ●​ If two species have long sequences of DNA or proteins that match closely, these sequences were likely copied from a common ancestor ○​ The greater the similarity in protein structure the more recent their common ancestry EVIDENCE FOR NATURAL SELECTION 1. ARTIFICIAL SELECTION ●​ Artificial selection: the selective breeding of domesticated plants and animals to produce offspring with genetic traits that humans value. ○​ Allows for rapid changes in a species in a short amount of time 2. ANTIBIOTIC RESISTANCE ●​ When bacteria evolve mechanisms that allow them to survive and multiply in the presence of antibiotics, making infections more difficult to treat ●​ When exposed to antibiotics, bacteria that are already resistant to the drug are more likely to survive and multiply MICROEVOLUTION GENE POOL ●​ Microevolution: A generation-to-generation change in the frequencies of alleles within a population ○​ In other words, changes that occur over time within a species on a small scale ●​ Gene pool: Consists of all of the alleles in the individuals that make up a species population ○​ The ‘reservoir’ from which the next generation draws its genes ○​ Where genetic variation is stored SOURCES OF VARIATION 1. Mutation: A change in the sequence of DNA ●​ Results because of mistakes in DNA replication (random) or exposure to chemicals/radiation ●​ Can improve, decrease, or have no effect on an organism’s fitness 2. Sexual Reproduction: Scrambling of existing alleles ●​ Meiosis (formation of eggs and sperm) and fertilization shuffle the alleles and recombine them (each offspring receives a new combination of alleles) ●​ Differences among individuals are largely the result of sexual recombination HARDY-WEINBERG EQUILIBRIUM ●​ Hardy-Weinberg Equilibrium: Populations that do not undergo changes to their gene pool (not evolving) ○​ Allele frequencies will stay the same across generations ●​ The equilibrium is maintained if: ➔​ No selection (equal fitness) ➔​ Random mating (no preference of genotypes) ➔​ No mutations ➔​ Large population (infinite) ➔​ No immigration/emigration MECHANISMS OF MICROEVOLUTION NATURAL SELECTION: ●​ Not a random process - one/a combination of alleles makes an organism more or less fit ●​ Stabilizing selection: Individuals with the most common variant of a trait are selected ○​ Different from average are selected against ○​ Results in the reduction of extreme values ●​ Directional selection: One extreme variant of a trait is favoured over the average variant