Chapter 11: EVIDENCE OF EVOLUTION

1. Chapter 11: EVIDENCE OF EVOLUTION PART 2

2. THE FOSSIL RECORD • FOSSILS ARE RECOGNIZED AS STONE-HARD EVIDENCE OF EARLIER LIFE FORMS. • HARD BODY PARTS SUCH AS TEETH, SHEELS, SEEDS, AND SPORES BECOME FOSSILS. • THESE FOSSILS ALONG WITH TRACE FOSSILS SUCH AS FOOTPRINTS, NESTS, BURROWS, TRAILS, EGGSHELLS, AND FECES CAN TELL ABOUT THE BODY STRUCTURE AND ACTIVITIES OF LONG DEAD ORGANISMS.

3. THE FOSSIL RECORD • FOSSILS ARE FOUND IN LAYERS OF SEDIMENTARY ROCKS. • WE STUDY LAYERS OF SEDIMENTARY ROCK TO UNDERSTAND NOT ONLY THE ORGANISMS FROM WHICH THE FOSSILS CAME BUT ALSO THEIR ENVIRONMENT AT THE TIME. • DEEPER LAYERS OF ROCK WERE DEPOITED FIRST AND SO CONTAIN OLDER FOSSILS, WHILE THOSE CLOSER TO THE SURFACE WERE DEPOSITED MORE RECENTLY. • THE COMPOSITION OF A ROCK LAYER AND ITS THICKNESS RELATIVE TO OTHER LAYERS CAN ALSO TELL US ABOUT LOCAL OR GLOBAL EVENTS THAT WERE OCCURRING AS THE LAYER FORMED.

4. THE FOSSIL RECORD

5. THE FOSSIL RECORD • WE HAVE FOSSILS FOR MORE THAN 250,000 KNOWN SPECIES; HOWEVER, WE KNOW THERE MUST HAVE BEEN MANY, MANY MORE THAT WE WILL NEVER KNOW ABOUT BECAUSE FOSSILS ARE RELATIVELY RARE. • USUALLY, REMAINS OF ANIMALS ARE QUICKLY DEVOURED BY SCAVENGERS OR DESTROYED BY DECAY. • SINCE OYGEN SPEEDS THE DECOMPOSITION OF REMAINS, FOSSILS ONLY FORM IF REMAINS ARE ENCASED IN MATERIALS THAT EXCLUDE AIR SUCH AS TAR, SAP, ICE, OR MUD. • FOSSILS THAT DO FORM ARE ALSO SUBJECT TO DESTRUCTION, DEFORMATION, OR SCATTERING BY EROSION OR OTHER GEOLOGIC PROCESSES. • CONSIDERING ALL OF THESE FACTS, IT SEEMS A MIRACLE THAT ANY INTACT FOSSILS WOULD BE FOUND AT ALL!!

6. THE FOSSIL RECORD • LUCKILY, THE FOSSIL RECORD IS SUBSTANTIAL ENOUGH SO THAT WE RECONSTRUCT PATTERNS IN THE HISTORY OF LIFE. • FOR EXAMPLE, EVOLUTIONARY BIOLOGISTS HAD ALWAYS THOUGHT THAT THE ANCESTORS OF WHALES LIVED ON LAND BECAUSE THE SKULL AND LOWER JAW OF ANIMALS SUCH AS WHALES, DOLPHINS, AND PORPOISES HAVE FEATURES VERY SIMILAR TO ANCIENT CARNIVOROUS LAND ANIMALS. • RECENT DNA SEQUENCE COMPARISONS SUGGESTED THAT THESE ANCESTORS WERE PROBABLY ARTIODACTYLS. • ARTIODACTYLS WERE HOOVED MAMMALS WITH TWO OR FOUR TOES ON EACH FOOT.

8. THE FOSSIL RECORD • WE HAVE FOSSILS SKELETONS THAT REPRESENT THE GRADUAL CHANGES BETWEEN THE ARTIODACTYLS AND WHALES, BUT THESE SKELETONS WERE INCOMPLETE SO PROOF OF THE EXACT TRANSITION REMAINED ELUSIVE UNTIL, IN 2000, ARCHAEOLOGISTS UNEARTHED THE COMPELTE SKELETONS OF TWO ANCIENT WHALES IN PAKISTAN. • THESE FOSSILS CONTAINED TWO ANKLE BONES AND ANCIENT WHALE-LIKE SKULL BONES, PROVIDING CLEAR EVIDENCE THAT THE ANCESTORS OF WHALES MADE THE TRANSITION FROM LAND TO WATER.

9. RADIOMETRIC DATING • A RADIOISOTOPE IS A FORM OF AN ELEMENT WITH AN UNSTABLE NUCLEUS THAT DECAYS TO PRODUCE A NEW ELEMENT AT A CONSTANT RATE WITH PREDICTABLE PRODUCTS. • THIS DECAY IS NOT INFLUENCED BY ANYTHING EXCEPT TIME. • FOR EXAMPLE, THE TIME IT TAKES FOR HALF OF A SAMPLE OF URANIUM-238 TO DECAY INTO LEAD-206 IS CALLED URANIUM’S HALF-LIFE. • THE HALF-LIFE OF URANIUM-238 IS 4.5 BILLION YEARS. • LIKE THE TICKING OF A PERFECT CLOCK, THIS TIME NEVER VARIES. • WE CAN USE THE PREDICTABILITY OF THIS RADIOACTIVE DECAY TO FIND THE AGE OF ANY ROCK.

10. RADIOMETRIC DATING

11. RADIOMETRIC DATING • RADIOMETRIC DATING IS A METHOD THAT CAN REVEAL THE AGE OF A MATERIAL BY MEASURING HOW MUCH OF A RADIOISOTOPE AND ITS PRODUCTS THAT THE SAMPLE CONTAINS.

12. RADIOMETRIC DATING • FOR EXAMPLE, WHEN MOLTEN ROCK DEEP INSIDE REACHES THE EARTH’S SURFACE, IT COOLS. • AS IT COOLS, THE MINERALS IT CONTAINS CRYSTALLIZE. • EACH TYPE OF MINERAL FORMS ITS OWN UNIQUE CRYSTALLINE SHAPE AND HAS ITS OWN UNIQUE COMPOSITION.

13. RADIOMETRIC DATING • THE MINERAL ZIRCON, FOR EXAMPLE, CONSISTS OF A VERY ORDERED STRUCTURE OF ZIRCON SILICATE MOLECULES. • SOME OF THESE ZIRCON CRYSTALS MAY HAVE URANIUM ATOMS SUBSTITUTED FOR ZIRCONIUM ATOMS, BUT NEVER CONTAIN LEAD. • OVER TIME, HOWEVER, THE URANIUM ATOMS CONTAINED WITHIN THESE CRYSTALS DECAY INTO LEAD AT A PREDICTABLE RATE. • AS TIME GOES ON, URANIUM ATOMS DISAPPEAR AND LEAD ATOMS BUILD UP IN THE CRYSTALS. • SCIENTISTS CAN MEASURE THE RATIO OF URANIUM ATOMS TO LEAD ATOMS AND USE THIS T=RATIO TO CALCULATE THE AGE OF THE CRYSTAL.

14. RADIOMETRIC DATING

15. PUTTING TIME INTO PERSPECTIVE • RADIOMETRIC DATING AND FOSSILS ALLOW US TO RECOGNIZE SIMILAR LAYERS OF ROCKS AROUND THE WORLD.

16. DRIFTING CONTINENTS, CHANGING SEAS • NOT ONLY DOES THE SURFACE OF THE EARTH CHANGE, BUT SO DOES THE EARTH ITSELF. • ONE MODEL SAYS THAT ALL CONTINENTS WERE ONCE PART OF A BIGGER SUPERCONTINENT CALLED PANGEA. • THIS MODEL SAYS THAT PANGEA SPLIT APART, FORMING ALL OF THE CONTINENTS THAT EXIST TODAY. • MOST SCIENTISTS DID NOT ACCEPT THIS MODEL, WHICH IS CALLED CONTINENTAL DRIFT.

17. PANGEA

18. DRIFTING CONTINENTS, CHANGING SEAS • HOWEVER, EVIDENCE THAT SUPPORTS THIS MODEL KEPT POPPING UP. • THE COASTS OF SOUTH AMERICA AND AFRICA SEEM TO FIT TOGETHER LIKE PUZZLE PIECES. • THE MAGENTIC POLES OF ROCK FORMATIONS ON DIFFERENT CONTINENTS ARE ALIGNED, BUT NOT NORTH TO SOUTH LIKE THEY WOULD BE IF THE CONTINENTS HAD NEVER MOVED. THE MAGENTIC POLES OF ROCK FORMATIONS ON DIFFERENT CONTINENTS POINT IN DIFFERENT DIRECTIONS, INDICATING THAT THE CONTINENTS HAVE MOVED. • DEEP SEA EXPOLERES HAVE ALSO DISCOVERED OCEAN FLOORS ARE NOT STATIC BUT THAT MOLETEN ROCK SPEWS OUT OF THEM, PUSHING OLD SEA FLOOR IN BOTH DIRECTIONS WHILE FORMING NEW.

19. DRIFTING CONTINENTS, CHANGING SEAS • BY THE CONTINENTAL DRIFT MECHANISM, EARTH’S RELATIVELY THIN OUTER ROCK LAYER IS CRACKED INTO LARGE PLATES, SIMILAR TO A CRACKED EGGSHELL. • THESE PLATES GROW FROM UNDERSEA RIDGES AND CONTINENTAL RIFTS AND SINK INTO DEEP SEA TRENCHES. • AS THE PLATES MOVE, THEY CARRY THE CONTINENTS ON TOP OF THEM TO NEW LOCATIONS. • THIS MOVEMENT IS ONLY ABOUT 10 CENTIMETEERS (4 INCHES) A YEAR, WHICH IS ABOUT HALF AS FAST AS YOUR TOENAILS GROW. • HOWEVER, ITS ENOUGH TO CARRY CONTINENTS ALL THE WAY AROUND THE WORLD AFTER 40 MILLION YEARS.

20. DRIFTING CONTINENTS, CHANGING SEAS • THIS THEORY OF CONTINENTAL MOVEMENT IS NOW CALLED PLATE TECTONICS ANDE EXPLAINED SOME LONG-STANDING PUZZLES. • FOR EXAMPLE, FOSSILS OF A TYPE OF FERN AND AN EARLY REPTILE WERE FOUND IN ROCK FORMATION THAT OCCURS IN AFRICA, INDIA, SOUTH AMERICA, AND AUSTRALIA. • THE ROCK FORMATION HAS A VERY COMPLEX SEQUENCE OF ROCK LAYERS THAT IS UNLIKELY TO HAVE FORMED IN MORE THAN ONE PLACE IN THE WORLD. • THIS ROCK FORMATION ALSO PREDATES PANGEA, SINCE IT IS 260 MILLION YEARS OLD, WHILE PANGEA BEGAN FORMING ONLY 237 MILLION YEARS AGO. • SO HOW DID THE FOSSILS OF THIS FERN AND REPTILE AND PORTIONS OF THIS UNUSUAL ROCK FORMATION COME TO BE ON SO MANY DIFFERENT CONTINENTS IF IT WAS FORMED EVEN BEFORE PANGEA??

21. DRIFTING CONTINENTS, CHANGING SEAS • THE FERN’S SEEDS WERE TO HEAVY TO HAVE FLOATED OR HAVE BEEN CARRIED BY THE WIND ACROSS CONTINENTS. • THE REPTILE WAS NOT BUILT TO SWIM ACROSS OCEANS. • RESEARCHERS SUSPECTED THAT BOTH ORGANISMS EVOLVED ON A SUPERCONTINENT THAT HAD BROKEN UP LONG BEFORE PANGEA FORMED. • THIS OLDER SUPERCONTINENT, NAMED GONDWANA, INCLUDED MOST OF THE LAND MASSES NOW IN THE SOUTHERN HEMISPHERE AS WELL AS INDIA AND ARABIA. • IF GONDWANA HAD REALLY EXISTED, RESEARCHERS PREDICTED THAT FOSSILS OF THIS FERN AND REPTILE SHOULD ALSO BE PRESENT IN ANARTICA, WHICH WAS MOST UNEXPLORED AT THE TIME. • SINCE THEN, EXPEDITIONS TO ANTARTICA HAVE UNCOVERED FOSSILS OF THE FERN AND THE REPTILE.

22. GONDWANA

23. DRIFTING CONTINENTS, CHANGING SEAS • IN FACT, SCIENTISTS HAVE DETERMINED THAT, SINCE EARTH’S OUTER LAYER OF ROCK SOLIDIFIED 4.55 BILLION YEARS AGO, A SINGLE SUPERCONTINENT WITH ONE LARGE OCEAN HAS FORMED AND THEN SPLIT UP AGAIN AT LEAST FIVE DIFFERENT TIMES. • THIS HAS HAD A PROFOUND IMPACT ON THE COURSE OF THE EVOLUTION OF LIFE. • THIS HAS AFFECTED CLIMATE ON CONTINENTS SINCE CONTINENTS’ CLIMATES CHANGE WITH THEIR POSITION ON EARTH. • CONTINENTS COLLIDING HAVE CAUSED THE PHYSICAL SEPARATION OF OF ORGANISMS LIVING IN THE OCEAN AND BROUGHT TOGETHER THOSE LIVING APART ON LAND. • CONTINENTS BREAKING UP HAVE SEPARATED ORGANISMS LIVING ON LAND AND BROUGHT TOGETHER THOSELIVING IN THE OCEAN. • LINEAGES THAT COULD NOT ADAPT TO THESE CHANGES HAVE DIED OUT, WHILE SURVIVING ONES HAVE BEEN PRESENTED WITH NEW OPPORTUNITIES.

24. SIMILARITIES IN BODY FORM AND FUNCTION • NOT ONLY DO WE HAVE FOSSIL EVIDENCE THAT EVOLUTION HAS OCCURRED, BUT WE ALSO HAVE ANIMALS THAT ARE ALIVE TODAY WHO PROVIDE MORE EVIDENCE FOR EVOLUTION. • SCIENTISTS CAN USE COMPARATIVE MORPHOLOGY TO PROVIDE CLUES AS TO HOW ORGANISMS HAVE EVOLVED BECAUSE SIMILARITIES IN THE STRUCTURE OF BODY PARTS ARE OFTEN EVIDENCE OF A COMMON ANCESTOR. • HOMOLOGOUS STRUCTURES ARE SIMILAR BODY PARTS THAT REFLECT SHARED ANCESTRY. • EVEN THOUGH THESE STRUCTURES MAY BE USED FOR DIFFERENT PURPOSES, THEIR DEVELOPMENT IS DIRECTED BY SIMILAR GENES SO THEY HAVE SIMILAR STRUCTURES.

25. SIMILARITIES IN BODY FORM AND FUNCTION • HOMOLOGOUS STRUCTURES, THOUGH THEY APPEAR QUITE DIFFERENT IN DIFFERENT LINEAGES OF ORGANISMS, THEY ARE QUITE SIMILAR IN THEIR UNDERLYING FORM. • FOR EXAMPLE, THE MANY FOREARMS OF MANY DIFFERENT VERTEBRATES ARE NOT THE SAME SIZE, SHAPRE, AND DO NOT HAVE THE SAME FUNCTION, YET THEY ARE CLEARLY ALIKE IN THE STRUCTURE AND POSITIONING OF BONY ELEMENTS, AS WELL AS IN THE PATTERNS OF BLOOD VESSELS, NERVES, AND MUSCLES ASSOCIATED WITH THEM. • FURTHERMORE, WHEN EARLY EMBRYOS OF THE DIFFERENT VERTEBRATES ARE COMPARED, A STRONG RESEMBLANCE IS PATTERN OF BONE DEVELOPMENT IS OBVIOUS. • THESE FACTS ARE CLEAR EVIDENCE OF SHARED ANCESTRY.

26. HOMOLOGOUS STRUCTURES

27. SIMILARITIES IN BODY FORM AND FUNCTION • POPULATIONS THAT DON’T INTERBREED SEPARATE BOTH GENETICALLY AND MORPHOLOGICALLY (IN BODY FORM). • THIS CHANGE IN BODY FORM FROM A COMMON ANCESTOR IS CALLED MORPHOLOGICAL DIVERGENCE. • HOMOLOGOUS STRUCTURES DEVELOP AS A RESULT OF THIS MORPHOLOGICAL DIVERGENCE.

28. SIMILARITIES IN BODY FORM AND FUNCTION • SIMILAR BODY PARTS ARE NOT ALWAYS HOMOLOGOUS. • SIMILAR STRUCTURES CAN EVOLVE INDEPENDENTLY IN DIFFERENT LINEAGES IN ORDER FOR ORGANISMS TO ADAPT TO SIMILAR ENVIRONMENTAL PRESSURES. • SUCH ANALOGOUS STRUCTURES LOOK ALIKE IN DIFFERENT LINEAGES BUT DO NOT HAVE SIMILAR UNDERLYING INTERNAL STRUCTURES AND, SO, DO NOT INDICATE SHARED ANCESTRY. • THE EVOLUTION OF SIMILAR BODY PARTS IN DIFFERENT LINEAGES IS CALLED MORPHOLOGICAL CONVERGENCE.

29. SIMILARITIES IN BODY FORM AND FUNCTION • AN EXAMPLE OF ANALOGOUS STRUCTURES ARISING BY MOROPHOLOGICAL CONVERGENCE WOULD BE INSECT, BAT, AND BIRD WINGS. • THOUGH ALL HAVE THE SAME FUNCTION- TO ENABLE FLIGHT- THEY HAVE DIFFERENT INTERNAL STRUCTURES.

30. ANALOGOUS STRUCTURES

31. SIMILARITIES IN BODY FORM AND FUCNTION • MASTER GENES DIRECT THE DEVELOPMENT OF AN EMBRYO INTO THE BODY OF A PLANT OR ANIMAL. • THE FAILURE OR MUTATION OF ANY SINGLE MASTER GENE CAN RESULT IN A DRASTICALLY ALTERED BODY PLAN , USUALLY WITH DEVASTATING RESULTS. • THEREFORE, THESE MASTER GENES TEND TO BE HIGHLY CONSERVED, MEANING THEY HAVE CHANGED VERY LITTLE IF AT ALL OVER EVOLUTIONARY TIME. • THUS, A MASTER GENE WITH SIMILAR SEQUENCE AND FUNCTION ACROSS DIFFERENT LINEAGES IS EVIDENCE THAT THESE LINEAGES ARE RELATED.

32. SIMILARITIES IN BODY FORM AND FUNCTION • FOR EXAMPLE, MASTER GENES CALLED HOMEOTIC GENES DIRECT THE DEVELOPMENT OF SPECIFIC BODY PARTS DURING EMBRYONIC DEVELOPEMNT. • A MUTATION IN ONE OF THESE GENES CAN ALTER AN ORGANISM’S BODY FORM DRASTICALLY SO THESE GENES ARE HIGHLY CONSERVED IN RELATED ORGANISMS. • WHEN THE SAME MASTER GENES DIRECT THE DEVELOPMENT, EMRYOS OF DIFFERENT ORGANISMS DEVELOP IN SIMILAR WAYS.

33. COMPARATIVE EMBRYOLOGY

34. BIOCHEMICAL SIMILARITIES • WE CAN COMAPRE DNA SEQUENCES AND AMINO ACID SEQUENCES OF PROTEINS OF PROTEINS TO DETERMINE RELATEDNESS OF ONE ORGANISM TO ANOTHER ALSO. • INEVITABLE MUTATIONS IN THE DNA SEQUENCE OCCUR OVER TIME. • THE PROCESS OF MUTATION IS RANDOM SO THESE CHANGES CAN OCCUR ANYWHERE IN A CHROMOSOME. • SINCE MOST MUTATIONS ARE NEUTRAL, MEANING THEY HAVE NO EFFECT ON ON THE FITNESS OF AN ORGANISM AND SO ARE NOT SELECTED FOR OR AGAINST BY NATURAL SELECTION, MUTATIONS ACCUMULATE IN DNA OVER TIME.

35. BIOCHEMICAL SIMILARITIES • SINCE MUTATIONS OCCUR AT A PREDICTABLE RATE, THE NUMBER OF ACCUMULATED DIFFERENCES BETWEEN SPECIES INDICATES HOW LONG AGO THEY SHARED A COMMON ANCESTOR. • THE MORE RECENT THE DIVERGENCE, THE LESS TIME THERE HAS BEEN FOR MUTATIONS TO ACCUMULATE. • THIS IS WHY THE DNA SEQUENCES OF TWO CLOSELY RELATED ORGANISMS IS MORE SIMILAR THAN THOSE OF MORE DISTANTLY RELATED SPECIES. • DNA SEQUENCING AND DNA FINGERPRINTING HAVE MADE COMPARING THE DNA SEQUENCES OF DIFFERENT SPECIES VERY FAST AND ACCURATE SO THAT COMAPRING DNA SEQUENCES TO DETERMINE RELATEDNESS IS NOW A COMMON PRACTICE.

36. BIOCHEMICAL SIMILARITIES • AMINO ACID SEQUENCES OF PROTEINS ARE ALSO USED O DETERMINE RELATEDNESS AMONG SPECIES. • TWO SPECIES WITH MANY IDENTICAL PROTEINS ARE MORE LIKELY TO BE CLOSELY RELATED THAN THOSE WITH FEW SIMILAR PROTEINS. • MORE UNRELATED SPECIES HAVE MORE DIFFERENT PROTEINS BECAUSE IT HAS BEEN SO LONG SINCE THEY HAVE SHARED A COMMON ANCESTOR THAT THERE HAS BEEN TIME FOR MANY MUTATIONS TO ACCUMUALTE IN THE DNA SEQUENCES.

37. BIOCHEMICAL SIMILARITIES THIS ALSO ILLUSTRATES HOMEOTIC (MASTER) GENE CONSERVATION

38. Homework • Which evidence for evolution that was presented in this chapter do you find most compelling and why? Explain.