Evolution after Darwin

Transcription

1 Evolution after Darwin

2 Evolution After Darwin

3 Peppered Moth (Biston betularia) as classic example of natural selection

4 Peppered Moth populations respond to changing environment (pollution).

5 Why has the theory of natural selection been so controversial?

6 Early Advocates of Nat. Selection After Darwin, advocates of evolution by NS were the minority view: P A.R. Wallace P as more committed to NS than Darwin P Exception made for human characteristics.

7 Early Advocates of Nat. Selection: August Weismann P Argued that soft inheritance was not possible P concept of germ-plasm P Mouse tail experiment P Work polarized evolutionary biologists.

8 Early Advocates of Nat. Selection: Francis Galton P Cousin of Charles Darwin P Quantitative inheritance P nature vs. nurture P Twin studies P Eugenics Movement Karl Pearson P Statistics as a discipline P Struggle between races P Arguments of racial superiority

9 Alternatives to Natural Selection P Problems with Natural Selection P Non-teleological; mechanistic P Non-directed process difficult to account for complexity P Assumed short geological time frame P Neo-Lamarckism positives P Acquired characteristics P Lack of good model of inheritance P Somewhat teleological P Consistent with concept of progress P Orthogenesis P Internal drive/development over time P Analogy to embryonic development P Very teleological and progressive

10 Alternatives to Natural Selection P Mutationism P Rediscovery of Mendelian laws of inheritance 1900 P Seen as alternative to natural selection P Traits appear qualitative P Evolution by mutational jumps? P Anti-gradualistic; saltational evolution P Discredits neo-lamarckism

11 The Rise of Population Genetics Early in the 20th century the basics of population genetics were developed by Yule, Hardy & Weinberg. Populations = collections of genotypes that change over time. Forces that affect population genetics: Natural selection Mutation Migration Nonrandom mating Genetic Drift

12 The Rise of Population Genetics In the 1920s, R.A. Fisher, J.B.S. Haldane, and Sewell Wright used complex mathematical models of population genetics to show how microevolution could occur. Quantitative vs. qualitative genetics Multiple, additive gene inheritance solves dilemma Fisher emphasizes large, homogeneous populations with alternate alleles Survival probabilities and fitness give new allele frequencies Fisher another example of eugenic connection to natural selection

13 The Rise of Population Genetics Sewell Wright emphasizes variations within small subpopulations Diversity stored in isolated populations Diversity is positive; counter to eugenics proposition

14 The Modern Synthesis Theodosius Dobzhansky Ukrainian emigree to US Evolution = change in allele frequency of a gene pool Genetic variation stored in diverse populations the key to responding to changing environments Skeptical of Fischer s simplistic models Eastern Orthodox; evolutionary creation Biology and faith argue against eugenics.

15 The Modern Synthesis Ernst Mayr Ornithologist; field biology; natural history Biological species concept Speciation process reproductive isolation Allopatric change; sympatry; postzygotic isolating mechanisms; prezygotic isolating mechanisms Isolated populations and founder effect

16 The Modern Synthesis P George Gaylord Simpson related paleontology (fossils) to neo- Darwinism. P Book Tempo and Mode in Evolution P Microevolution of population genetics extrapolated to macroevolution of the fossil record P Lamarckism, saltationism, orthogenesis not applicable to fossils Before Simpson: linear evo. After Simpson: branching bush

17 The Modern Synthesis P G. Ledyard Stebbins applied the modern synthesis to plants. P Hybridization, polyploidy and speciation in plants P Natural selection, but also rapid speciation

18 The Modern Synthesis Julian Huxley (grandson of Thomas Henry Huxley) Authored Evolution: The Modern Synthesis Spokesperson and popularizer of the modern synthesis.

19 Tenets of the Synthesis The 1950s & 1960s neo-darwinist research program: P Mutation & selection as described by population geneticists are responsible for evolutionary change. P Populations are homogenous, with only minor amounts of genetic variation. P All characteristics of speices should be explainable in terms of natural selection. P Evolutionary change is gradual. P Evolution is directionless and not goal-oriented. P Natural chemical processes led to the origin of life. P Behavior (including human) is explained in terms of selection at the level of individual genes (the sociobiological research program). True altruism is an illusion.

20 Contribution of Molecular Biology P Discovery of extensive molecular variability in populations (beginning in the >60s) challenged the view that selection for optimal alleles should lead to few optimal genotypes. P Kimura and others advocated the neutral theory of molecular evolution. P While challenging extreme selectionism, comparison of similar molecules led to development of molecular phylogenies. P Discovery of the complex interactions between genes raises questions about the validity of a Abean-bag@ approach to genes and natural selection. P Discovery of the existence of gene duplication, introns/exons, and gene regulatory apparatus challenged the traditional view of evolution by point mutations within genes.

21 Stephen J Gould

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23 The spandrels of San Marcos and the Panglossian Paradigm are all characteristics really adaptations?

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27 The Challenge of Punctuated Equilibrium Paleontologists Stephen J. Gould & Niles Eldridge formulate the theory of Punctuated Equilibrium, that emphasized: P Differing rates of evolution to account for the fossil record: stasis punctuated by rapid evolution associated with speciation events. P The role of chance events such as founder effect and genetic drift in the origin of new species. P Non-adapted traits due to pleiotropy and allometric effects. P Selection at multiple levels, such as species selection. P The role of chance events in the overall history of life.

28 Self-Organization; Evo-devo P Failure of point mutations to provide for large-scale evolutionary change challenges early view of modern synthesis. P Non-linear dynamics points to the importance of small changes in initial conditions, leading to what is termed Achaos.@ P The field of chaos theory suggests that some higher levels of order arise from seemingly chaotic systems. P Kaufmann and others challenge the place of natural selection in developing complex systems. They argue that order can arise naturally by Aself-organization.@ P Much current evolutionary theory proposes changes due to the timing and expression of genes, rather than changes within genes. P Mutations to gene promoter and enhancer regions can alter gene expression P These changes lead to developmental changes that alter the phenotype (evolutionary developmental genetics; evo-devo )

29 P Much current evolutionary theory proposes changes due to the timing and expression of genes, rather than changes within genes. P Mutations to gene promoter and enhancer regions can alter gene expression P These changes lead to developmental changes that alter the phenotype (evolutionary developmental genetics; evo-devo )

30 P Much current evolutionary theory proposes changes due to the timing and expression of genes, rather than changes within genes. P Mutations to gene promoter and enhancer regions can alter gene expression P These changes lead to developmental changes that alter the phenotype (evolutionary developmental genetics; evo-devo )

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32 Religious Responses P Conservative theology P Liberal theology P Emphasis on morality; progress P Pluralistic P Orthodoxy P Traditional doctrines realistic, but not literal P Fundamentalism 1910 & following P Originally more concerned with higher criticism of the bible P Literalism emerges from fundamentalism P Eventually opposes evolution P Whitcomb & Morris Genesis Flood 1961 creation science P Neo-orthodoxy 1930 & following P Arises in Germany in response to co-opted state church P God understood by revelation - Barth P Independence of science and faith P Process theology 1930 & following P Integrates views from modern quantum physics; ecology P Emphasizes interactions rather than entities

33 Philosophical & Religious Challenges P Other evangelical biologists chose to affirm progressive creationism or theistic understandings of evolution. (e.g. American Scientific Affiliation) P Philosophers such as Popper questioned the philosophical status of evolutionary theory (60s and on). P Beginning in the 80's more sophisticated critiques of evolutionary anomalies began to appear (e.g. Denton, Behe, Dembski), leading to the Intelligent Design movement. P Others such as Johnson challenge the scientistic worldview assumptions associated with evolution. P The sociobiological research program has been challenged by those who feel it does not adequately explain the complexity of human nature. P Other Christians find compatibility of evolutionary biology with Christian faith (e.g. Francis Collins, Ken Miller, Biologos )