Chapters 17 & 18

2. Chapters 17 & 18 Evolution and Natural Selection

3. Evolutionary theory • Originally described by Charles Darwin. • On The Origin of Species, 1859 • There are slight variations in traits of a species. • These traits are inheritable. • Some of these traits increase an organism’s chances of survival and reproduction. • Those individuals who survive and reproduce pass along their genetic material (“survival of the fittest”).

4. Evolutionary Theory • The offspring are more likely to have the variation of the trait that allowed better survival & reproduction. • Natural selection—individuals with beneficial traits are more likely to survive and pass on these traits • With each generation, there are slight modifications in traits. • Over enough time, modifications accumulate so that eventually the population is very different from the ancestral organisms.

5. Evolutionary theory • Darwin theorized a gradual, continual change • Not supported by fossil record • More recent scientists have suggested “punctuated equilibrium”: long periods of no or minor change, followed by short periods of dramatic change Amount of Change Amount of Change Time Time Gradualism Punctuated Equilibrium

6. Evolutionary theory • Origin of life • 4.4 billion years ago • Began with simple chemicals, gradually became more complex through bonding • Eventually these formed amino acids • As polypeptides formed, eventually became simple life • Primitive organisms (cells) likely in ancient oceans

7. Evolutionary theory • Natural selection resulted in more complex single-celled organisms • Benefit to working together • These eventually evolved into multi-celled organisms • Organisms changed based on evolutionary pressures

8. Evolutionary theory • Organisms starting moving onto land • Those who had traits that increased their survival on land evolved • Organisms continued to evolve and modify based on environmental pressures • Most “fit” of each generation would survive • Over time the changes led to completely new organisms

9. Evolutionary theory—animals

10. Evolutionary theory—animals

11. Evidence—fossils • Older fossils show fewer variety of organisms • Older fossils show more primitive features • Newer fossils show changes and progression among characteristics • New characteristics appear in newer fossils • The complexity of organisms increases when looking at newer versus older fossils

12. Evidence—fossils • Transitional forms • “Missing links” • Archaeopteryx • Eustheopteron • Seymouria

13. Evidence—fossils • Problems? • Radiocarbon dating may not be accurate • Inaccuracies have been calculated (dating volcanic rock known to be 200 years old as billions of years old) • Some transitional forms questioned • Archaeopteryx likely an extinct species and not a bird ancestor • Fewer than expected transitional forms • Living, unevolved “fossils” • Coelacanth— “extinct” 80 million years ago, rediscovered 1938

14. Evidence—origin of life • Several experiments have created simple organic molecules under “primitive Earth” conditions • “Building blocks” for life • Fossilized bacteria • Living multicellular colonies • Portuguese Man o’ War

15. Evidence—origin of life • Problems? • Dispute and debate over conditions of primitive Earth • No proven mechanism for evolving from simple compounds to primitive cells • Spontaneous generation? • “Life” from “unlife” • Many theories, often conflicting • Really an unanswered question

16. Evidence—anatomy • Homologous structures—similarities in body parts between groups. • Morphological divergence—Variations in structures of different species based on a basic form in a common ancestor

17. Evidence--anatomy • Problems? • Different genes can produce homologous structures • Body segments in fruit flies and wasps • The same gene can produce non-homologous structures

18. Evidence—biogeographical • Similar species in different parts of the world • Rheas, emus, ostriches • Common ancestor, separated because of plate tectonics (movement of sections of the earth’s crust)

19. Evidence—biogeographical • Rhea—South America • Emu—Australia • Ostrich—Africa

20. Evidence—mutations • Theory—mutations of DNA (insertion, deletion, inversion, translocation, duplication, etc.) can result in new traits or features. These are random events. • If these new features give the organism a survival advantage, they are more likely to be passed along.

21. Evidence—mutations • Mutations do happen (well established) • Mutations can be beneficial • Bacterial resistance to antibiotics • Sickle cell anemia giving resistance to malaria • Resistance to atherosclerosis in Italian village

22. Evidence—mutations • Problems? • Virtually all mutations are harmful or neutral • Many new traits created in lab are not seen in the wild (fruit flies) • New structures do not mean benefit • Second pair of fruit fly wings lack muscles and harm flight ability • Truly beneficial mutations only found in bacteria & other single-celled organisms • Beneficial “mutations” often can be argued to be recessive traits that already exist • Mutations really beneficial? • Sickle-cell anemia

23. Evidence—DNA • Similar DNA sequences in many species • The more closely they appear to be related, the more DNA is shared • Humans & bananas: 50-60% • Humans & worms: 75% • Humans & chimpanzees: 98% • The less DNA in common, the more distant the common ancestor

24. Evidence—DNA & proteins • Problems? • Small differences in DNA can mean big differences in appearance & function • Similarities could result from similar actions & functions, in the same way that sports cars share similarities with each other, but not with SUVs

25. Evidence—natural selection • Populations evolve, not organisms • Phenotypic variation • Morphological—physical features • Physiological—metabolic activities and products • Behavioral—responses to situations and stimuli • Gene pool—possible trait variations within a population

26. Evidence—natural selection • Mutation changes or creates new alleles • Other factors shuffle existing alleles • Crossing over (Meiosis I) • Homologous chromosome arrangement (Meiosis I) • Fertilization • Some alleles have greater frequencies in the population than others • Red hair • Albinism • Allele frequencies can change over time

27. Evidence—natural selection • Natural selection— “Survival of the fittest”. Some traits allow individuals to survive or reproduce better than others. These traits therefore increase in a population. • Three types • Directional • Stabilizing • Disruptive

28. Evidence—natural selection • Directional selection—Natural selection “favors” a phenotype, increasing the frequency of this allele • Peppered Moth • Two variant phenotypes • Pre-industrial, light were more common • After industrial pollution, dark were more common

29. Evidence—natural selection • Stabilizing selection—Intermediate forms of a trait are favored, extreme forms are not • Human birth weight • Very large or very small babies less likely to survive compared to average-sized

30. Evidence—natural selection • Disruptive selection—Extreme forms of variation are favored, intermediate forms selected against • “Darwin’s” finches • Speculated to be derived from common ancestor • Different beaks adapted for different foods

31. Evidence—natural selection • Natural selection (“microevolution”) is readily accepted, even by critics • “Classic” examples not unchallenged • Questions of validity of peppered moth studies • Galapagos finches show variations in bills, but return to “normal”

32. Verdict? • Scientists overwhelmingly support evolution • Much is still not understood about the processes involved • Many intelligent, non-religious people have problems with aspects of evolutionary theory • Darwin’s theories have always been challenged • Much evidence for AND against evolution • Decisions need to be made on facts and science

33. Evolution vs. creation • Evolution • Evolution is a Fact • Creationist Claims • TalkOrigins Archive • Evolution Evidence • Creationism/Intelligent Design/Anti-Evolution • Answers In Genesis (home of the Creation Museum) • Institute for Creation Research • Science Against Evolution • Darwinism Refuted • YouTube Videos • Forum presenting both sides in various discussions • Main page • Thread giving sources for both views