Evolution: descent with modification

1. Evolution: descent with modification • Genetic change over time in a common ancestor which makes an organism more suited for an environment • Unifying principle of all biological sciences • Universally accepted fact • What factors can change DNA over time? • DNA changes can result in organismal changes • Phenotype vs genotype

2. Evolutionary Terms • Adaptive trait-any form or function that allows an organism to survive in its current environment • Fitness-measure of reproduction, ability to produce viable and fertile offspring • Gene pool-all the genes of a population • Allele-different forms of a gene (trait) • Mutation-change in the DNA; the original source of genetic variation

3. History of Evolutionary Thought and Ideas • 400 BC Plato, Aristole: Every object was an imperfect copy of an ideal form; diversity of organisms some more complex than others, species organized by degree of complexity • 1400s Century Global exploration: discovery of organisms never seen before • 1600s discovery of fossils; organisms that were no longer found on earth, but they were similar to some still alive

4. History of Evolutionary Thought and Ideas • 1700s Carolus Linnaeus began taxonomy of living organisms based on differences and similarities (binomial nomenclature) • 1700s Leclerc (Count Buffon) documented with evidence descent with modification  generation after generation, will result in variation • 1700s Erasmus Darwin (Charles’ grandfather) wrote on common descent based on development, artificial selection, vestigial structures • 1798 Malthus, population size correlates with famine, disease, war • 1830 Lyell, “Principle’s of Geology” by studying the earth’s layers, natural catastrophes, determined that the earth was not 6000 years old, but millions

5. History of Evolutionary Thought and Ideas • 1700s careful studies of differences and similarities between organisms, Lamarck’s Inheritance of Acquired Characteristics, giraffe’s neck and the “stretching” hypothesis; genotypes are inherited- not necessarily phenotypes • 1700s Cuvier founded paleontology and catastrophism after a natural disaster or extinction new species from surrounding areas repopulated area; used to explain the variation of fossils in different stratum layers

6. History of Evolutionary Thought and Ideas • 1831 Charles Darwin 5 year voyage around the world on the HMS Beagle. • S America and The Galapagos islands; collected over 200K species, observed massive geological changes, stratification of earth’s layers, read Lyell’s Principles of Geology

7. History of Evolutionary Thought and Ideas • Found fossil of glyptodonts-ancestors of current day armadillo • Could the armadillo come from this? • A change would require millions of years; earth must be olderLyell suggested the earth was much older than 6000 years and the observed changes occurred gradually over long periods of time

8. History of Evolutionary Thought and Ideas • Darwin looked at the biogeography of organisms • No rabbits in SA, but Patagonian hares, same niche…different ancestors? • In Galapagos Islands (965 km from mainland) tortoises with different lengths of necks, and finches with different sizes of beaks, depending on island they were located and food source available • Could the tortoises/finches on the islands come from an ancestor on the mainland?

9. History of Evolutionary Thought and Ideas: Darwin • Darwin’s Finches-Galapagos Islands • Depending on the island and resources available, nectar vs. seed size, the birds beaks were different, yet they were finches

10. History of Evolutionary Thought and Ideas: Darwin • Looked at dog breeding; wolf  dog • Artificial Selection by humans produced different dog breeds. • Could there be a natural selection process not driven by humans but by environmental factors?

11. Variation in Populations • Why is there so much species diversity? Yet, so many common traits? • What Factors Produce Genetic Variability in a Population? • Crossing Over-prophase I, Meiosis • Independent assortment-metaphase I, Meiosis • Chromosome number changes-nondisjunction in Anaphase, mitosis/meiosis • Chromosome structure changes-deletions, duplications, translocations, inversions • Mutations-somatic vs. germ cells, silent • Fertilization-1 sperm + 1 egg

12. Darwin’s Theory of Natural Selection • Through his travels to SA and Galapagos Islands, collecting and observing different species • By reading the works of other scientists who presented data on geology, anatomy, competition, population size, and artificial selection • Darwin published “The Origin of the Species” which contained Natural Selection as a mechanism that drives Evolution

13. Natural selection: Obs. 1) All species have great potential fertility and population size would increase exponentially if all born reproduced successfully Obs. 3) Environmental resources are limited Obs. 2) Populations tend to remain stable in size -Inference 1: Production of more individuals than the environment can support leads to a struggle for survival; only a fraction survive Obs. 4) Individuals vary, no 2 individuals are exactly alike Obs. 5) Variation is heritable -Inference 2: Survival is not random; those individuals with beneficial inherited traits will leave more offspring Differential reproductive success

14. -Inference 3: This differential reproduction leads to gradual change in populations; the product of natural selection is adaptation of populations to their environment

15. Natural selection and Evolution selects Natural Selection individual phenotype drives over time Evolution is change in genotype frequency of population Individuals do not evolve; populations do ex.English Peppered Moth

16. Factors That Drive Natural Selection • Competition for limited resources • High reproductive rates • Variability and adaptability of traits • Heritability of traits

17. Natural Selection is Observable • Darwin’ finches  beak depth • Peppered moths  switch from light to dark color • Marine snail  thickness of shell • Honey creeper  beak smaller • Bacteria  antibiotic resistance • Cancer cells/HIV  drug resistance

18. Evidence for Evolution • Fossils-buried remains and mineralized impression of organisms from the past; older fossils  deeper sediment layers • Transitional fossils-an organism that shows features from 2 different lineages; intermediate form, common ancestor • Archaeopteryxtransitional form between reptiles and birds • Ambulocetus terrestrial ancestor of whales

19. The Fossil Record • Only those organisms with hard parts preserved the best • Have to find the fossil • Some fossils not intact; erosion, water and earth movement, predators • Complete records for many lineages have been found. Ex. Horse

20. The evolution of the horse involves the gradual development of the modern horse from the fox-sized, forest-dwelling Hyracotherium. Paleozoologists have been able to piece together a more complete picture of the modern horse's evolutionary lineage than that of any other animal.

21. Evidence for Evolution • Biogeography • Study of the range and distribution of organisms on earth • When organisms are related, they evolved in one region and spread to other accessible regions • Different organisms would be expected when geography separates land masses, islands, oceans

22. Evidence for Evolution • Comparative Morphology • Study of bone structures and body organization between different organisms • Looking for similar structures with similar functions between groups • Stem reptile forearm has homologous structures that are found in human, bat, porpoise, penguin, chicken, pterosaur • Analogous structures: bird vs. bat vs. insect wing

23. Evidence for Evolution • Comparative Embryology • Study of embryos and early development patterns between different organisms • Early embryos (up to 6 weeks) of humans, fish, chicken, reptile look identical. Why? • Human embryos have gill slits, webbed fingers/toes, tail, fur • Vestigial structures: features that are fully developed in one group of organisms but are reduced and have no function in similar groups • Must have same ancient instructions (DNA); variations in later development due to mutations and transposons

24. Evidence for Evolution • Comparative Molecular Biology: all living organisms use the same hereditary molecules; these molecules were present in the first living cell and have been passed to all extant organisms • Study differences/similarities of proteins. Many “housekeeping” enzymes will be the same in function, but not aa sequence between organisms • Study differences/similarities of DNA sequences. The more closely related the DNA sequence between 2 organisms, the more closely related they are to each other. Humans and chimps DNA are 99% identical