Natural Selection and Evolution

1. Changes in Populations over Time Natural Selection and Evolution

2. Chapter 22 Objectives 1. Define evolution. 2. Discuss several observations which suggest relatedness between different species. Note observations of both fossil and living organisms. 3. Explain the fundamental principles that form the foundation of Darwin’s Theory. Including: • The relationship between population size and famine, disease, . . . • Variability of traits within a population • Heritability of physical traits • The role of environmental factors on the utility of traits

3. Chapter 22 Objectives 4. Explain how the processes of artificial and natural selection can cause changes in a population over time. 5. Discuss the following types of evidence as they relate to the evolutionary view. Give examples: • Comparative morphology • Comparative embryology/development • Comparative biochemistry/genetics

4. Do Populations Evolve? • Species can be as much alike as wolves and coyotes, or as different as plants and animals • And although plants and animals are superficially very different, at the chemical and cellular level they share a number of similarities • Are the similarities superficial or are they the result of ancestral relationships? • Are the differences distinct or are they variations on a fundamental theme?

5. Paleontology Studies of fossils show a number of interesting things: • Species existed that no longer exist • Many organisms that are extinct bear strong resemblance to species that exist today • Most species that exist today did not exist at some time in the past

6. Comments on the Scientific Method • The nature of a hypothesis is more than just a guess, it must follow a few simple rules: • A good hypothesis must be consistent with all available data and observations • A good hypothesis should logically extend to accurate predictions of both past and future observations (particularly those that will be the results of controlled experiments) • In other words, a good hypothesis shouldn’t just make sense, it should create the expectation of exactly the types of things that are being observed

7. Two Alternative Hypotheses Species are fixed and distinct: • Fixed = unchanging • Distinct = separate/unrelated • Biblical creationism and “intelligent design” theory are more consistent with this hypothesis Species change over time: • Change = “evolution” • The assumption of any ancestral relationship between species must also assume that populations have evolved from the time of the ancestor to modern time • Modern taxonomy is based on this hypothesis

8. A quick clarification: • It is possible for species to be distinct, but to still evolve. • Changes within a population (“microevolution”) do not necessarily mean that a particular species shares an ancestral relationship with another species (“macroevolution“) • The same logic doesn’t hold in the other direction though • For example, wolves could evolve, and coyotes could evolve, but that doesn’t mean coyotes and wolves necessarily evolved from a common ancestor • But if wolves and coyotes share a common ancestor they must have evolved since then, because they aren’t the same species now

9. Evaluating the Hypotheses • Large variations (at the level of Kingdom, phylum, and class) seem to favor the “fixed and distinct” hypothesis. • The differences between prokaryotes and eukaryotes, or between plants and animals, seem to be more than simple variations • Variations at the lower taxonomic levels (genus and species) seem to indicate some closer level of relationship • Wolves, coyotes, foxes, and domestic dogs seem to be very much alike - so much alike, for example, that they can hybridize in some cases

10. Evaluating the Hypotheses • Remember, a good hypothesis should not only be consistent with the data, it should also predict outcomes • The “fixed and distinct” hypothesis doesn’t demand that species should never resemble each other, but it does nothing to explain why they ever would • It also gives us no explanation for why extinct organisms found in fossils should have any resemblance at all to species alive today • It certainly is inconsistent with any amount of hybridization between species • And perhaps of greatest importance, it gives us no explanation for the presence of species today that are not represented at earlier times in the fossil record

11. With that being said . . . • The “fixed and distinct” hypothesis becomes difficult to evaluate any further. • But in order to accept the “evolution” hypothesis we will need to: • Demonstrate a mechanism for change that predicts the pattern of similarities and differences we can observe • Create a series of controlled experiments that result in changes within a population over time • Devise a method for quantifying the position a population occupies at any given time so that we can re-evaluate the same population to identify any changes that may have occurred • Apply that method to populations “in the field” to look for natural changes

12. A preview of things to come • Darwin proposed a mechanism of change we will call Natural Selection • We will also consider Artificial Selection, and see how it serves as a controlled experiment to evaluate population change (Objectives #3 & 4) • We will become familiar with the Hardy-Weinberg hypothesis and the calculations it utilizes to evaluate stability and change within a population (Objectives #6 & 7) • We will evaluate our student population using the Hardy-Weinberg equations and perform simulations of populations exposed to different conditions

13. Mechanisms of Change - Darwin • Charles Darwin proposed a mechanism for evolution by “Natural Selection” • You are responsible for making yourself familiar with the historical background and basis for Darwin’s ideas by reading sections 22.1 and 22.2 in the textbook • You are also expected to be familiar with an alternative mechanism for evolution as proposed by Jean Baptiste de Lamarck (22.1) • Here’s a video that can help in that regard: • http://www.youtube.com/watch?v=V8KIvICfGEMhttp://www.youtube.com/watch?v=V8KIvICfGEM

14. The Foundation of Natural Selection Premise #1 There is variation within populations with regard to inherited traits • Variability within a population results from a variety of factors, including: • Conjugation, Transformation and Transduction (in microorganisms) • Sexual Reproduction, Independent Assortment and Crossing Over • Mutations • Variable expression of genes • Variable post-transcriptional gene processing (in eukaryotes) • http://www.youtube.com/watch?v=UjMn4oHfYL4&index=44&list=PLFCE4D99C4124A27A

15. The Foundation of Natural Selection Premise #2 Populations experience a Struggle for Existence • This struggle is largely imposed upon the population by environmental stresses • Availability of food and other resources • Predators • Communicable Disease • Harsh climatic conditions • Some of these environmental stresses become more significant as populations become more dense

17. Natural Selection • Is natural because natural forces (environmental factors) select (choose) which individuals in a population will survive and reproduce • Traits which interfere with survival will quickly become extinct within that population • They will be “selected against” • Traits which provide advantages will quickly become the predominant characteristics within that population • They will be “selected for” • http://www.youtube.com/watch?annotation_id=annotation_3856240253&feature=iv&src_vid=UuGrBhK2c7U&v=hOfRN0KihOU#t=10shttp://www.youtube.com/watch?annotation_id=annotation_3856240253&feature=iv&src_vid=UuGrBhK2c7U&v=hOfRN0KihOU#t=10s

18. Some more Video • http://www.youtube.com/watch?v=R6La6_kIr9g&index=3&list=PLFCE4D99C4124A27A • http://www.youtube.com/watch?v=S7EhExhXOPQ&index=4&list=PLFCE4D99C4124A27A

19. But I digress . . . • Richard Dawkins, in his book The Selfish Gene, applied the concept of natural selection to any “self-replicating agent”. Basically, he said that any replicator that replicates more than others will tend to appear more frequently in the larger pool of replicators. • Biologically speaking, the fundamental unit of replication is a gene. So any gene that successfully promotes its own replication will tend to increase its frequency in the “gene pool”

20. But I digress . . . • But Dawkins extended this out to include things like ideas, social norms, and such things. He termed non-biological replicators “memes” • So internet “memes” are traceable back to Dawkins, and through Dawkins back to Darwin

21. Logical Extensions of the Hypothesis • The same population, exposed to a different set of environmental conditions, will evolve based on the stresses imposed by that environment

22. Logical Extensions of the Hypothesis • Segments of populations that migrate to new areas will evolve differently than the populations they leave behind

23. Logical Extensions of the Hypothesis • Organisms living in the same environment, but employing different strategies (“ecological niches”) will evolve to be well adapted to the needs and stresses of that particular niche

24. Logical Extensions of the Hypothesis • Populations exposed to rapid environmental change will evolve rapidly, while those exposed to gradual change will evolve gradually Phyletic Gradualism Punctuated Equilibrium

25. Sounds good, but does it work? • We’re scientists, so we can’t just take a hypothesis at face value. We need to test the hypothesis with a controlled experiment. • A controlled experiment would require: • Simulating the conditions of natural selection • Begin with a population that has variability for some inherited trait • Create a circumstance that results in differential rates of survival/reproduction • Manipulating the independent variable • Impose a selecting pressure on the population • Observing the results in the dependent variable • See if the population changes over time (generations)

26. It’s called Artificial Selection • Farmers have been doing it with crops and livestock for as long as there have been farmers. Every domestic crop and domesticated animal is the result of Artificial Selection (“selective breeding”) • We can come up with any number of examples. So do that. Now. • Super Cow Breeders: • http://www.youtube.com/watch?v=rW54_vM9SF0 • Dog Breeding: • http://www.youtube.com/watch?v=tukxnJ8Gnbghttp://www.youtube.com/watch?v=tukxnJ8Gnbg • http://www.youtube.com/watch?v=kPWDusnGgP8&feature=related • Horse Breeding • http://www.youtube.com/watch?v=_rHZCtwl-hwhttp://www.youtube.com/watch?v=_rHZCtwl-hw

27. But does it really happen in Nature? • The Peppered Moth • http://www.youtube.com/watch?v=LyRA807djLc • Antibiotic Resistant Bacteria • http://www.youtube.com/watch?v=v-Peboq0AqA • The Evolution of Speed • http://www.youtube.com/watch?v=Gm0uCPmB0Ng • Jaws • http://www.youtube.com/watch?v=PP3HmDGs8G4&list=PLNtcr2FLR4dfstWMcH25YEllfPbc3VmS3 • Eyes • http://www.youtube.com/watch?v=qV_TKi266bE

28. How do we evaluate past Evolution • Comparative Morphology • Morphology is body form • If species share common ancestry, they should have similarities in body form • Comparative Embryology/Development • Ancestry is more evident in embryonic development than it is in adulthood • Comparative Biochemistry/Genetics • At its most fundamental, it isn’t traits that are inherited, it is genes • Genes are located on chromosomes, and code for the production of proteins

29. Remember Natural selection acts on variable traits that already exist in the population • You can’t use something that you don’t already have • What you can do is use something you do have, but use it in a different way or for a different purpose

30. Comparative Morphology • If this really happens, we should see organisms with the same basic anatomical features, but adapting them to different purposes (Homologous structures) • We should also see features with no value to their owners become diminished (Vestigial structures) • And where a particular way of life is especially effective, we should see a wide variety of unrelated organisms adapting to that way of life, using whatever anatomical features they have at their disposal (Analogous structures)

31. Homology in Finch Beaks • The birds shown are all finches • In each, the beak is adapted to eating a different type of food • These finches are descendants of a common ancestor from the South American mainland • An ancestral population migrated to the Galapagos Islands where they diverged by evolving to different environments

32. Homology in Plants • All of these structures are derived from leaves • Their development is derived from the same embryonic tissues • Each is modified to a different specialized function

33. Homology in Vertebrate Forelimbs

34. Skeletal Homology

35. Homologous vs Analagous

36. Homology and Analogy in Wings

37. Homology and Analogy

38. Analogy in Marine Vertebrates • Dolphins • http://www.youtube.com/watch?v=AGyuO7LaOco • Sharks • http://www.youtube.com/watch?v=o81WIfjrt5I • Penguins • http://www.youtube.com/watch?v=A9mbCNs47FI • Seals • http://www.youtube.com/watch?v=cQu4M--MRbc

39. Vestigial StructuresPersistant but Diminished

40. Vestigial StructuresPersistent but Diminished

41. Vestigial Structures • Why persistent? • Because the genes for those structures still exist • Why diminished? • Because the expression of a gene is expensive • Transcription costs energy because each nucleotide must be tri-phosphorylated • Translation costs raw materials because amino acids used to express that gene are tied up and not available for expression of other genes

42. Comparative Embryology/Development • Early embryonic development shows marked similarity between even very distantly related forms of life • As diverse as vertebrates are, they all share a number of embryonic features • Cranium • Pharyngeal gill slits • Post anal tail • Segmented vertebrae

43. Comparative BiochemistryAmino Acid Sequences

44. Comparative Biochemistry & GeneticsNucleotide Base Sequences

45. Comparative Biochemistry & GeneticsChromosomal Comparisons • Remember that in Karyotyping, homologous chromosomes are identified by size, shape, location of the centromere, and banding patterns. • While karyotypes match homologous chromosomes from the same cell, the same techniques can be used to search for regions of homology in chromosomes from different species

46. Chapter 23 Objectives 6. Define species & population. 7. Use the Hardy-Weinberg principle to evaluate stability or change in allele frequencies within a population. 8. Define Genetic Drift. Discuss how population size effects genetic drift. Note circumstances which might cause drastic changes in population size.

47. Chapter 23 Objectives 9. Explain and give examples of each of the following types of natural selection • Directional • Stabilizing • Disruptive 10. Explain how sexual selection differs from natural selection. Give examples. 11. Explain several ways in which genetic variability might arise within a population.

48. Chapter 24 Objectives 1. Explain the biological species concept. Contrast this concept with other methods of defining species 2. Contrast gene flow with reproductive isolation. Discuss the effects of isolation on the gene pool of a population. 3. Contrast prezygotic and postzygotic barriers to reproduction 4. Discuss several mechanisms of reproductive isolation.

49. Chapter 24 Objectives 5. Define speciation. 6. Discuss circumstances which might logically result in speciation. 7. Distinguish between allopatric, sympatric, and parapatric speciation. 8. Make and interpret diagrams representing patterns of evolution and speciation. 9. Distinguish between gradual and punctuated speciation.

50. Chapter 25 Objectives 10. Discuss the conditions of the early earth 11. Discuss several hypotheses regarding the chemistry of formation of macromolecules on the early earth 12. Discuss circumstances which favor the formation of fossils. Recognize several different types of fossils. 13. State the Law of Superposition and use it to infer the relative age of fossils. 14. Explain the process of radiometric dating