Life Science 15: Concepts and IssuesLecture 4: Darwin’s dangerous idea1/19/12I. The evolution of starvation resistanceII. What is evolution?III. What is natural selection?Q: How long can a fly live without food? Can we increase the average time to starvation in a population?- normal= 20 hours until death- what if we only let the ‘best’ flies reproduce? (top 20%)- after one generation: 21 hrs until death- after ten generations: 28 hrs until death- after 60 generations: 60 hrs until deathSpecies are not immutable. We can watch them change in nature or even cause them to change.Could we use the same experimental approach to change other populations?-turkeys now cannot mate due to large breast muscles-milk production in cowsWhat is evolution?-a gradual process in which something changes into a different and usually more complex or better form-a change in allele frequencies over time within a populationGene: section of DNA instructing how to produce a traitAllele: one variant of a gene (several may exist)We each carry 2 copies of every gene (one from each parent)-alleles can be the same: BB/bb (homozygous)-alleles can be different: Bb (heterozygous)-we can measure the frequency of B and bCharles Darwin:- lazy teenager- med school drop out- 1831-86: HMS beagle trip around world- provocative observations- years of thinking1. Finch variation-each island has unique species-island species resembled mainland species-maybe they used to be the same species?2. Similarity between fossils of extinct species and the living species in an area-extinct glyptodon looked like GIANT armadilloCommon themes in nature:- offspring overproduction (how many survive to adulthood)- competition for scarce resources- inheritance of traitsStruggle for existence:- organisms better suited to an environment have a greater probability of surviving the struggle and will leave more offspring.Almost scooped by Alfred Russel Wallace- published togetherTriumph: published his own book, his “abstract”- “The Origin of Species”Conditions for Natural Selection:1. variation2. heritability3. differential reproductive successIf the 3 conditions are fulfilled, evolution by natural selection is occurring. Types of Selection:1. Directional selection (milk production in cows)2. Stabilizing selection (birth weight)3. Disruptive selection (body size of salmon)Persistent selection (many generations) can dramatically change the morphology, behavior, and physiology of the individuals in a