These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute. Lecture 4 Outline of Last Lecture I. The Enlightenment of the 18th Century and major Naturalist Theories a. Carolus Linneaus b. William Smith c. William Paley d. Lamarck e. Malthus f. Lyell II. Development of Charles Darwin’s Theory a. Voyage on the HMS Beagle b. Galapagos Islands c. Alfred Russell Wallace Outline of Current Lecture II. Adaptive evolution a. Darwin’s Four Postulates of Evolution b. Natural Selection: Evidence that the Four Postulates are Accurate c. The Grants’ Medium Ground Finch Experiment: Witnessing evolution Current Lecture Adaptive evolution • Adaptation: is a process and a physical trait • Natural selection leads to adaptation • Darwin’s Logic: four Postulates of Evolution o 1.Individuals in a population vary. o 2. Traits are passed from parents to offspring ! These first two ideas combine to give us the idea of Heritable variation o 3. Individuals vary in surviving and reproducing ! This is classified as differential reproductive success o 4. Survival and reproduction are not just due to chance ! These factors lead to the difference in survival and reproductive chances ! Heritable variation and reproductive success are correlated o If all these four postulates are accurate than the frequencies of traits will change over generations. • Adaptive evolution by Natural selection • Evidence that these four postulates are accurate BIO 280 1st Editiono From observing the Galapagos finches, Darwin recognized that these birds all have a common ancestor of a mainland bird. Speciation comes from this common ancestor. This leads to the branching out of different physiological features. • On Daphne Island The Grants observed the Medium Ground Finch over the course of 30 years o Beak depth was widely variable in this population" Postulate 1 is observably true. o The Grants averaged the beak size of the parents and they averaged the beak size of offspring to see if size was inherited ! Possible Problem" It is possible that environmental factors effect beak depth ex) some offspring are fed better than others ! The Grants used a method called Linear regression combat this potential problem" best fitting line through these varying points. Steeper the slope meant greater the heritability ! Their statistical analysis proved postulate 2 of heritability of variable traits o Postulate 3, Organisms vary in success at surviving and reproducing ! Note on Biotic Potential: ! If reproductive success didn’t vary than the following estimates would be true • Estimation Darwin" 19 million elephants in 750 yr • Estimation Dodson" 10^79 starfish in 16 yr ! Clearly more organisms are born than live and reproduce o The Grants observed that over the course of 20 years there were significantly less finches on the island. There were so few that the Grants could count them all and completely eliminate error in mean beak size. Mean value of birds decreased" so not all of them survived o From these results, Postulate 4 is proven. Survival was not random because over the years of the drought, the average of the beak size shifted upwardly showing that the average of the breeding offspring had bigger beaks than the average beak size of the parent population" This difference is known as the selection differential o Grants found that before the drought, seeds were small and soft. After the seeds were large and hard" those who could handle the harder seeds survived. So the larger beaks survived. o Looking solely at birds that hatched after the drought" only the offspring of the surviving generation" Mean beak size shifted in offspring showing adaptive evolution. The population adapted to have larger numbers of large beaks" When you only look at trait frequency in a population that was derived from the parent population, this is known as response to selection • Why was the response to selection different in 2004? (Why did the average beak size decrease again?) o Decrease in beak size. o Hint: large ground finch appeared on Daphne in 1982o Hypothesis: These larger ground finch probably outcompeted the medium ground finch for the larger harder seeds during the second drought" forcing a shift of medium ground finch beak size to smaller depth as to accommodate a different food source than the large ground finch. o This process is called character displacement" favors the two extremes" when selective forces push the traits of the two species apart" so those who had large beaks in large ground finches survived and those who had small beaks in medium ground finches o To conclude, the Grants witnessed "Natural selection acts on individuals and populations evolve. Natural selection determines who lives and who dies" need that selection due to difference and heritability for evolution o The medium ground finches were experiencing Competitive exclusion" exclusion of larger beaks in medium ground finch because It was