1. Fossils & Evolution, Ch. 51 Chapter 5—Key concepts The “modern synthesis” or “Neo-Darwinism” emerged in the 1930’s and 1940’s when population genetics was linked with natural selection as the primary mechanism of evolutionary change. Extreme Neo- Darwinists believe that all evolution is “microevolution” (i.e., gradual changes, added up over hundreds of generations, to produce new anatomical features, new species, and new fundamental body plans). Beginning in the 1970’s, the concept of “macroevolution” has challenged extreme Neo-Darwinism. According to macroevolution, large-scale evolutionary changes do not occur as a result of gradual, stepwise processes, but more abruptly. Macroevolution is supported by the discovery of regulatory genes. A slightly different meaning of “macroevolution” involves phylogenetic evolutionary trends: i.e., trends above the species level.

2. Fossils & Evolution, Ch. 52 Chapter 5—Key terms Neo-Darwinism (= modern evolutionary synthesis) Microevolution (phyletic evolution) Macroevolution (phylogenetic evolution) Structural genes Regulatory genes

3. Fossils & Evolution, Ch. 53 Microevolution vs. Macroevolution These terms mean different things to different people Textbook author considers microevolution to mean gradual, generation upon generation change; and macroevolution to mean abrupt, saltational change potentially resulting in new anatomical features, new species, even new body plans

4. Fossils & Evolution, Ch. 54 Macroevolution = phylogenetic evolution (branching; evolution above the species level) Microevolution = phyletic evolution (evolution at the population/species level) Conventional meaning of microevolution and macroevolution

5. Fossils & Evolution, Ch. 55 Darwinian evolution Evolution = descent with modification –In natural populations, more offspring are produced than can be sustained in the environment –There is variation among individuals (because of mutations and genetic recombination during sexual reproduction) –Natural selection results in the differential survival of variants –Variation is heritable: therefore, advantageous traits are likely to be passed on from generation to generation

6. Fossils & Evolution, Ch. 56 Neo-Darwinism Population genetics = use of mathematical models to determine how mutation and natural selection can cause changes in gene frequencies in populations When population genetics was coupled with Darwinian selection, the so-called modern evolutionary synthesis emerged.

7. Fossils & Evolution, Ch. 57 Neo-Darwinism A tenet of Neo-Darwinism is the belief that all evolutionary changes can be attributed to repeated rounds of microevolution –Microevolution = small scale changes that occur in a few generations in response to natural selection –Phyletic evolution = Gradual changes, added up over hundreds of generations, can produce new anatomical features, new species, new body plans

8. Fossils & Evolution, Ch. 58 Exceptional evidence for Darwinian evolution in the deep-sea fossil record images courtesy of Ocean Drilling Program

9. Fossils & Evolution, Ch. 59 images courtesy of Ocean Drilling Program

10. Fossils & Evolution, Ch. 510 a b c Ap-W Ap-H Ch-Height Radius Ch-Width Diam. Axis Baselength Um-angle planktonic foraminifera Turborotalia image courtesy of Paul Pearson, Cardiff University

11. Fossils & Evolution, Ch. 511 image courtesy of Paul Pearson, Cardiff University 52 successive populations spanning ~12 million years (~0.25 m.y. increments)

12. Fossils & Evolution, Ch. 512 evolutionary trend images courtesy of Paul Pearson, Cardiff University

13. Fossils & Evolution, Ch. 513 ©Cushman Foundation for Foraminiferal Research T. frontosa T. pomeroli T. cerroazulensis chronospecies

14. Fossils & Evolution, Ch. 514 Neutralism An initial challenge to “extreme Neo-Darwinism” occurred when it was discovered that many genes are not expressed –If so, then how can natural selection act upon them? Much of the genetic code is “junk” –Amino acids are coded for by groups of three nucleotides (4 possible in each of three positions) –64 possible combinations –Yet, only 20 amino acids! –Third position in codon is largely redundant

15. Fossils & Evolution, Ch. 515 nucleotide bases: A = adenine C = cytosine G = guanine U = uracil phosphate sugar DNA double helix

16. Fossils & Evolution, Ch. 516 Third base in codon is largely redundant

17. Fossils & Evolution, Ch. 517 Macroevolution Macroevolution has emerged as a model for explaining the origin of major adaptive features –Not just repeated rounds of microevolution Example: hinged upper jawbone in bolyerine snakes (related to boas) –Hinge must have evolved abruptly as a novel feature, not gradually from an unhinged ancestral condition

18. Fossils & Evolution, Ch. 518 Boa constrictor (solid upper jaw) Bolyerine snake (hinged upper jaw)

19. Fossils & Evolution, Ch. 519 Macroevolution Macroevolutionary changes are supported by the discovery of regulatory genes –Structural genes code for individual proteins and structures –Regulatory genes are like “switches” that turn on or off the expression of other genes Small mutation in a regulatory gene can radically alter or silence the expression of a string of structural genes that it controls

20. Fossils & Evolution, Ch. 520 Horses still possess structural genes of their three-toed ancestors. When regulatory genes fail to suppress these structural genes, a three-toed horse develops

21. Fossils & Evolution, Ch. 521 Macroevolution Homeotic genes are special regulatory genes. Mutations to homeotic genes can cause abrupt transformations: –Antennipedia in flies (appendage grows on head instead of antenna)

22. Fossils & Evolution, Ch. 522 Macroevolution Hox complex of homeotic genes controls basic segmentation of body in arthropods and vertebrates –mutations to Hox genes can cause “stretched DC8”-type transformations)

23. Fossils & Evolution, Ch. 523 Stretched DC8 Natalie Gulbis

24. Fossils & Evolution, Ch. 524 Macroevolution (= phylogenetic evolution)

25. Fossils & Evolution, Ch. 525

26. Fossils & Evolution, Ch. 526

27. Fossils & Evolution, Ch. 527 Trend toward size increase in A, B, C Trend toward size decrease in D–F