Evolution: Constructing a Fundamental Scientific Theory

1. Evolution: Constructing a Fundamental Scientific Theory Chapter 2

2. Overview • We study both the past and present to understand human evolution • Part I: observing living populations • Part II: study of ancestors

3. Introduction • 1800s: explorations, discoveries of new lands, plants, animals, and people • Fossils: preserved remains • Charles Darwin went on a 5 year voyage on the HMS Beagle • Observed, studied, and collected specimens

4. Darwin • Began formulating questions about observations • Variation among and between species (finches) • Variation according to habitat • First explanation was “descent with modification” • Adaptations: variations in physical characteristics to fit the environment

6. Two Major Findings • 1. natural selection: • More individuals are born than can survive • Limited resources leads to competition • Those with advantages (adaptations) will survive and pass down genes • Those without will die • Primary driver of evolution • 2. adaptive radiation: out of one species branches closely related multiple species

8. Natural Selection: Practical Example

9. Natural selection is about biology, but in humans, it is also about intellect/knowledge • If you were stranded on a desert island, would you want the people you were with to be in shape, or to have specialized knowledge? • What types of knowledge would be helpful?

10. The main point is that natural selection is about what is advantageous in that specific environment at that specific time • On the island, it may be helpful for an animal to be fast, or small, or green • BUT, if the environment changes, this may not be the case • A computer programmer may have been successful beforehand, but will not have an advantage on the island

11. Practical Example #2 • Can you see viruses or bacteria? • They are alive and, like everything else, they evolve • Can evolve in a matter of hours • This is why not taking antibiotics/medication correctly leads to drug resistance

12. When people do not take medication correctly Yellow = weak viruses Purple = medium viruses Red = strong viruses

13. When people do not take medication correctly Yellow = weak viruses Purple = medium viruses Red = strong viruses

14. Theory of Evolution • Evolution just means change over time • Here, it means change in gene frequency over generations • Before Darwin, most explanations were based on religious beliefs • Earth is 6,000 years old, everything is fixed • Darwin used 5 disciplines: • Geology, paleontology, taxonomy/systematics, demography, evolutionary biology

15. Geology • Geology: study of earth in regard to composition, activity, and history • Earth is 4.6 billion years old • Hutton and Lyell found that forces (rain, wind) change the earth today just as they did in the past : uniformitarianism • Also found that land’s surfaces get stacked on top of each other: strata • These processes all take millions of years and can be observed and tested

17. Paleontology • Georges Cuvier pioneered comparative anatomy and paleontology • Reconstructed the appearance of fossil animals • Provided the first basic understanding of history of life • Catastrophism: catastrophic events (not evolution) are responsible for changes in Earth’s history • What is an example from the Bible? • What is an example from fossil history?

19. Taxonomy/Systematics • Taxonomies group living organisms according to similarities • Carolus Linnaeus gave each organism a genus and species: binomial nomenclature • At this time still adhered to biblical explanations. Taxonomies showed God’s intentions • Also some ranking (hierarchy) • Organisms are fixed and don’t change

20. Taxonomy of Humans • Kingdom Anamalia • Phylum Chordata • Class Mammalia • Order Primates • Family Hominidae • Genus Homo • Species sapiens

21. Demography • Darwin influenced by essay of Thomas Malthus • Said there was not enough food to feed every person born • Darwin applied these ideas to other living things • Those that survive are the ones equipped to compete for food and win

22. Evolutionary Biology • In late 1700s some scientists said organisms aren’t fixed and that they do change over time • Lamarck first discussed adaptations • He was correct in saying that animals adapt to their environment • Lamarkism or Prinicple of Acquired Characteristics: organisms pass on features they acquire during their lifetimes • Incorrect • hierarchy

23. Lamarckism • Example: if a giraffe needs to eat leaves at the very tops of tall trees, it should stretch its neck until he is the correct height. Then his offspring will be born with long necks • If you chopped off both hands right now, would your children be born without hands? • Why is Acquired Characteristics incorrect?

25. Darwin’s Theory of Evolution • Darwin used all of these fields to shape his idea • He saw that those best suited for their environment survived and passed down those traits. Those that weren’t suited died • Nature puts pressure on living things and selects the traits that are advantageous • Origin of Species (1859). After discovering and Wallace had the same idea, Darwin beat him to publication

26. ICA • Darwin vs. Lamarck

27. Since Darwin…Inheritance and DNA • Darwin and scientists at the time thought body was made of invisible particles called gemmules • Also thought blending inheritance • Gregor Mendel’s pea experiments uncovered idea of inheritance and dominant and recessive traits • Discrete traits • Mathematical laws • NO BLENDING!

29. Model of Genetic Events • Mendel said that inheritable traits keep their individuality by not blending • Principle of Segregation: offspring receive traits from parents, and the traits are kept in pairs that separate during formation of sex cells. • Principle of Independent Assortment: inheritance patterns of each trait are independent of one another • each trait has an equal chance of being inherited

30. Mendelian Genetics • Later scientists would discover genes: a section of DNA that codes for a trait and their alleles: different versions of genes • Each allele is either dominant or recessive • Dominant: T Recessive: t • One allele is from mom, the other is from dad • If both alleles are the same = homozygous • If both dominant = homozygous dominant • If both recessive = homozygous recessive • If one allele is dominant and one is recessive = heterozygous

31. Mendelian Genetics • The genotype is the genetic makeup of an organism. It is the coding of alleles the organism • For trait “T,” homozygous dominant is TT, homozygous recessive is tt and heterozygous is Tt • The phenotype is the physical expression of the gene. For trait “T” it would be taster or non-taster • Later, genes would be found inside chromosomes, where the heredity material is passed to offspring

33. Phenotypes Genotypes

34. Evolutionary Synthesis • Four mechanisms for evolution: • Mutation: a change in genetic information; adds new genetic material; can be good/bad/neutral • Gene flow: organism’s migrate and mate with a new group. The merging of new gene pools creates variation • Genetic drift: when a group is small, some traits are over-represented and some are under-represented • Natural selection

35. Questions to ponder… • How can you describe natural selection in your own terms? What are some examples? • How are Darwin’s and Lamarck’s theories similar and different? Is one correct and one incorrect? • How did Mendel discover how traits are inherited? What do his two principles show us?