Lecture 7.2 Introduction to Evolution NS 201 WW 2024 PDF

Introduction to Evolution NS 201 WW 2024 Cohen 1  Reminders Week 7 review opens Wednesday, due Monday ○ Includes lecture 6.1 (biodiversity), 7.2 (intro to evolution), and reading phylogenetic trees. Remember to fill out...

Introduction to Evolution NS 201 WW 2024 Cohen 1  Reminders Week 7 review opens Wednesday, due Monday ○ Includes lecture 6.1 (biodiversity), 7.2 (intro to evolution), and reading phylogenetic trees. Remember to fill out ○ Mid-semester feedback ○ Learning Strategies Inventory (Exam 1) 2  Evolution Evolution → descent with inherited modification Includes: Microevolution → changes in gene frequency over time Macroevolution → speciation 3 Evolution has produced the diversity of life on Earth 4  The 4 Evolutionary Forces Mutation Migration Selection ○ Natural Selection ○ Sexual Selection Genetic Drift 5 Darwin’s Theory of Natural Selection 6  Key Observation 1: Variation & Heritability Organisms within a species vary and these variations can be passed on from parent to offspring Evidence: Selective Breeding (Artificial Selection) Pigeon Fanciers (including Darwin) bred Pigeons Selective Breeding in Agriculture 7 Evolution by Natural Selection Individuals of a species are not all identical Variation can be: Advantageous Deleterious (bad) Neutral Variations are passed from parents to offspring Have a genetic basis 8  Key Observation 2: Overproduction All species produce more offspring than the environment can support, but populations remain stable. American Toads, Anaxyrus americanus, laying thousands of eggs 9 Evolution by Natural Selection Organisms produce more offspring than can survive Traits are passed whether they are beneficial or not 10 Evolution by Natural Selection Inference 1 → Selection Not all offspring produced will survive. Some individuals are more likely than others to reproduce because of their heritable traits 11  Evolution by Natural Selection Inference 2 → Evolution In each generation, traits change in frequency in the population as a result of differential survival and reproduction. 12  The Basis of Natural Selection (Darwin, 1859) Variation & Heritability Selection Evolution Observation: Individuals in a population vary. Inference 1: Inference 2: Many characteristics are Not all offspring As a result of this heritable. produced will difference in survive. survival and reproduction, Overproduction Some individuals beneficial traits are more likely Observation: will increase in than others to Populations have the frequency in the reproduce potential to increase population over because of their exponentially but they don’t - time. heritable traits. they remain relatively stable. Natural resources are limited. 13 Evolution by Natural Selection Evolution “Descent with modification” from a common ancestor (Darwin, 1837) Change in allele frequency in a gene pool (Dobzhansky, 1937) Natural selection One mechanism by which evolution occurs Darwin (1837) 14  Adaptation - a tricky word, often misused Adaptation (process) → The process by which a species (or population) becomes better fit to survive and reproduce in its environment over time. Adaptation is not something that an individual does. An individual does not adapt to its environment. Populations adapt over generations. Adaptation (noun)/Adaptive trait → a trait which serves a function in an organism, confers evolutionary fitness, and has been maintained by natural selection. 15  True or false: Variation that is acquired during an organism's lifetime can be acted on by selection. Click Present with Slido or install our Chrome extension to activate this ⓘ poll while presenting. 16  True or False: Most organisms produce more offspring than will survive. Click Present with Slido or install our Chrome extension to activate this ⓘ poll while presenting. 17  T/F: Under natural selection, survival is random - any organism has an equal chance of surviving. Click Present with Slido or install our Chrome extension to activate this ⓘ poll while presenting. 18  T/F: Evolution occurs when the frequency of a trait in a population changes over generations. Click Present with Slido or install our Chrome extension to activate this ⓘ poll while presenting. 19  An example from Darwin’s finches Beaks of finches are adapted to food source 20  An example from Darwin’s finches In dry years, average beak depth increased. Average beak depth for the population 21 An example from Darwin’s finches During drought, small seeds are scarce Birds with larger beaks can eat bigger seeds (less desirable food source) Birds with smaller beaks do not survive/reproduce Birds with larger beaks survive and reproduce and produce offspring with beaks on average 3-4% larger than their grandparents’ generation Average beak size changes over time 22  Example: Antibiotic Resistance Occurs when bacterial populations become resistant to the drugs used to kill them. Example: 1943 - Penicillin (antibiotic) discovered & used widely 1967 - Penicillin resistant Streptococcus pneumoniae (causes ear infections, pneumonia, sinus infections, pink eye) 23 (Source: CDC) How does antibiotic resistance evolve? 24  There is no INTENTION in natural selection Organisms are just existing, finding food, reproducing as is their natural instinct to do. Organisms pass on their traits whether they are beneficial or not - they can’t choose to have faster or bigger offspring. It is the environment - the selective pressure that determines any advantage of certain traits for survival/reproduction. Even a slight 1% advantage in survival can cause the proportion of a trait to gradually increase in a population over time. There are no “good” or “bad” traits - conditions in the environment can fluctuate, favoring different traits at different times 25  Natural selection is like a sieve - certain traits are favored over others, which are filtered out Selective Pressures: 1. Competition 2. Predation 3. Disease/parasitism 4. Climate/environment 5. Sexual Selection (mate choice) 6. Anthropogenic (human) - i.e. land use, pollution, climate change 26 Misconceptions About Evolution 27  Individuals Evolve Individuals do not evolve, populations do. Individual birds’ beak depth is not changing Average beak depth in the population is changing Individuals with larger beaks are surviving & reproducing at higher rates than individuals with smaller beaks 28  Organisms Evolve on Purpose Evolution works on variation that is already in a population - variation does not occur in response to and environmental change. The birds beaks had variation before the drought. Selection favored birds with larger beaks. Their beaks did not get larger in response to the drought. 29  Other misconceptions (THESE ARE NOT TRUE) Natural selection acts for the good of the species Evolution explains the origin of life Evolutionary theory implies that life evolved (and continues to evolve) randomly, or by chance. Evolution results in progress; organisms are always getting better through evolution. Read more misconceptions and their explanation here 30  What is wrong with the following statements about evolution? Discuss with neighbors and submit a response. 31  What's wrong with this statement? Snails evolved thicker shells in order to avoid predation. Click Present with Slido or install our Chrome extension to activate this ⓘ poll while presenting. 32  What's wrong here: Bacteria outsmart humans and learn to resist new antibiotics that humans use. Click Present with Slido or install our Chrome extension to activate this ⓘ poll while presenting. 33  Correct the statement: Evolution is completely random. Click Present with Slido or install our Chrome extension to activate this ⓘ poll while presenting. 34  Why is this wrong? After a bird migrated to a new island, it adapted to its new environment. Click Present with Slido or install our Chrome extension to activate this ⓘ poll while presenting. 35  Why is this wrong? Exposure to antibiotics causes bacteria to become resistant. Click Present with Slido or install our Chrome extension to activate this ⓘ poll while presenting. 36  What's wrong with this statement? The finches in the Galapagos were competing over seeds, so they evolved different beaks to eat different food sources. Click Present with Slido or install our Chrome extension to activate this ⓘ poll while presenting. 37  Summary Natural Selection Misconceptions about natural selection Variation & Heritability Selection Evolution Observation: Individuals in a population vary. Inference 1: Inference 2: Many characteristics are Not all offspring As a result of this heritable. produced will difference in survive. survival and reproduction, Overproduction Some individuals beneficial traits are more likely Observation: will increase in than others to Populations have the frequency in the reproduce potential to increase population over because of their exponentially but they don’t - time. heritable traits. they remain relatively stable. Natural resources are limited. 38