Evolutionary Theory, Past and Present

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•The Ascendency of Genetics & Population Studies. •The Modern Synthesis. • Recent Advances in Evolutionary Theory. History of evolutionary science after ...

Charles Darwin: Evolutionary Theory, Past and Present Evolutionary Science After Darwin

from C. Darwin, 1859, Origin of Species...

OUTLINE - Evolutionary Science After Darwin Introduction - understanding & misunderstanding of science compelling ideas that bear on origins - particularly touchy nature of scientific discovery v. non-scientific knowledge

Michael Ruse: the EVOUTION-CREATION struggle Conservative

Religion as politics

rapture Plato

Evangelical

I Christian intellectual tradition II

Mainstream Christian Mainstream “Secular” Materialist

Aristotle

progress 1600

C R I S I S

1700

Science as religion

Liberal 1800

1900

OUTLINE - Evolutionary Science After Darwin Introduction - understanding & misunderstanding of science ideas that bear on origins - particularly compelling nature of scientific discovery Matryoshka dolls

OUTLINE - Evolutionary Science After Darwin Introduction - understanding & misunderstanding of science ideas that bear on origins - particularly compelling nature of scientific discovery History of evolutionary science after 1859 •Problems with Darwin’s idea •Development of Alternatives Hypotheses •The Ascendency of Genetics & Population Studies •The Modern Synthesis •Recent Advances in Evolutionary Theory

PROBLEMS WITH DARWIN’S THEORY

HISTORICAL DEVELOPMENT OF EVOLUTIONARY THEORY G E O L O G Y

period of disfavor AGE OF EARTH UNIFORMITARIANISM

Un

ifo

POPULATION GENETICS FOSSILS EXTINCTION CATASTROPHISM ZOOLOGY CLASSIFICATION

NATURAL SELECTION

MODERN SYNTHESIS

GENETICS REVOLUTION

rm

ity

Gradualism Punctuated Equilibiria

B DOMESTIC I SELECTION BREEDING PALEONTOLOGY O HEREDITY MENDELIAN MOLECULAR e h L INHERITANCE BIOLOGY p VARIATION o r O BIOCHEMISTRY t s ADAPTATION G ta EXCESS REPRODUCTION a C Y STRUGGLE FOR SURVIVAL SELECTION BY ENVIRONMENT Political Rev. Industrial Revolution

1700's

1800's

1900's

Descent with Modification by means of Natural Selection 1) If individuals vary (in traits or characters), 2) If variations are inherited by offspring, 3) And if more offspring are born than can survive, competition (for space, food, other resources) will be intense in the struggle for existence. •As a result, variations (traits) that confer adaptive advantages will be favored (selected) and accumulate via differential reproductive success. •New species arise from pre-existing ones in response to the interaction of random variations with changes in environmental conditions; the development of new species is gradual, taking places over countless generations.

PREDICTIONS OF THE THEORY 1) Descent with modification, 2) From common ancestors, 3) Producing a branching tree of life, 4) Connected by many intermediate species, 5) Characterized by extinction of less fit taxa. 6) Variations acted on by selection are random, 7) So there is no direction or purpose evident in the history of life.

Difficulties with Darwin’s theory •Common ancestors, intermediate forms, and a branching tree of life were countered by detractors, but not disproven outright. …but relatively large jumps in morphology via selection of small random changes accumulating gradually over myriad generations? Very difficult to demonstrate…

Darwin’s argued…. •Changes occur in small populations (e.g., islands) •Geological record is highly imperfect = GAPS

But Sedgwick, Murchison, Smith, Cuvier, etc. Were developing a remarkable record of Earth history preserved in ancient strata…

Difficulties with Darwin’s theory •Common ancestors, intermediate forms, and a branching tree of life were countered by detractors, but not disproven outright. …but relatively large jumps in morphology via selection of small random changes accumulating gradually over myriad generations? Very difficult to demonstrate…

Darwin’s argued…. •Changes occur in small populations (e.g., islands) •Geological record is highly imperfect = GAPS •Natura non facit saltum - nature takes no leaps •Speciation requires VAST spans of time

William Thomson - Lord Kelvin (1824 –1907) Northern-Irish-born British (Ulster Scot) mathematical physicist and engineer.

In 1869 he calculated Earth’s age based on assumptions for (1) original temp., (2) current temp. dist., and (3) cooling rate by conduction: ~20 to 40 Myr ….WAY TOO SHORT for all known phyla to have evolved if only by slow, gradual natural selection. John Joly (University of Dublin) also estimated Earth’s age (1899) by calculating the rate at which oceans should have accumulated salt from erosion (80 to 100 Myr). Although loyal Darwinians did not accept these age estimates and their implications, until the discovery of radiometric dating (1908) there was a serious roadblock to widespread acceptance of natural selection.

Difficulties with Darwin’s theory

Selection IS a brilliant idea, but Darwin offered no credible mechanism for the sources of variation in natural populations He struggled with the prospect of “blending inheritance” and later editions of the Origin resorted to Lamarckian explanations for the source of new variations, and more...

40+ years of disfavor for natural selection DEVELOPMENT OF ALTERNATIVE IDEAS •Lamarckism - Darwin, Haeckel, etc. •Pangenesis - Darwin •Saltationism - Huxley, DeVries, Weismann, etc. •Orthogenesis - Eimer, etc. •Theistic evolution - Lyell, Asa Gray, etc.

Pangenesis

Charles Darwin’s hypothetical mechanism for heredity •body cells shed gemmules, which collect in the reproductive organs prior to fertilization. •every cell in the body has a 'vote' in the constitution of the offspring. •Atavisms (reversion to ancestral types) arise due to awaking of long-dormant gemmules, while limbs regenerate due to the activation of gemmules from the missing limb. Darwin’s failed attempt to integrate concepts of blending inheritance, Lamarckian use/disuse, and regeneration.

Sir Francis Galton (1822 –1911) Half-cousin of Charles Darwin, he was an English Victorian polymath.

•Invented concepts of correlation and regression; •Refuted Darwin's hypothetical theory of pangenesis; •Came close to rediscovering Mendel's particulate theory of inheritance; •Founded Biometric Approach to study of heredity, distinguished by use of statistical techniques to study continuous traits and population-scale aspects of heredity; •Formulated the ideology of Eugenics.

Lamarckism, 1860 - 90’s Ernst Haeckel (1834 —1919) Eminent German biologist, naturalist, philosopher, physician, professor and artist.

•Speculated that the nucleus transmitted heredity. •An advocate of Lamarckism. •In 1866, he proposed his Theory of Recapitulation (ontogeny recapitulates phylogeny). •Also an early Eugenecist.

Orthogenesis, 1890’s Gustav Eimer (1843–1898) German zoologist. …life has an innate tendency to move in a unilinear fashion due to due to restrictions in the direction of variation by some internal or external "driving force". The (extinct) Irish Elk

Saltationism, 1890’s F.L. August Weismann (1834 - 1914) German biologist Advocated the germ plasm theory… …inheritance only takes place by means of germ cells—gametes, such as egg and sperm. Other cells of the body somatic cells - do not function as agents of heredity. Referred to as the Weismann barrier, this invalidates Lamarckian inheritance of acquired characters. Variations occur from time to time in the individuals of a population, as a result of genetic mutations.

Hugo de Vries (1848 - 1935) Dutch botanist and one of the first geneticists; experimented extensively with evening primrose (Oenothera lamarckiana).

• In 1889 he published Intracellular Pangenesis, based on a modified version of Charles Darwin's theory of Pangenesis of 1868. •Later he rediscovered Gregor Mendel's laws of heredity (1890s) along with Carl Correns. •Among the first to suggest the concept of genes as discrete units of heredity. •He was first to develop a mutation theory of evolution.

William Bateson (1861 –1926) British geneticist, Fellow of St. John's College, Cambridge,

•Coined the term ‘genetics’ to describe the study of heredity and biological inheritance •Chief populariser of Gregor Mendel’s ideas following their rediscovery in 1900 by Hugo de Vries and Carl Correns. •Punnet, an assistant of Bateson, develops the Punnet Square. •A major proponent of Saltationism, which later became known as mutation theory.

…proposed that all evolutionary change could be accounted for by mutations - no need for selection.

ASCENDENCY OF GENETICS & POPULATION STUDIES

Gregor Johann Mendel (1822 –1884) Augustinian priest and scientist, often called father of genetics; worked out the laws of heredity by careful experimentation.

He performed experiments between 1856 and 1863 at the Augustinian Abbey of St. Thomas in Brno (Austria, now Czech Republic)... … cultivated and tested some 28,000 pea plants, through which he discovered mathematical patterns in the distribution of traits through successive generations. Based on this, he proposed ‘Laws of Inheritance.’

Gregor Mendel’s scientific work 8 years of breeding experiments on Pisum sativum - the garden pea; Mendel initially grew 34 varieties for 2 yrs to ensure pure strains, then chose 22 pure varieties and studied 7 specific traits in cross breeding experiments: 1.Plant height 2.Flower color 3.Flower position 4.Pod shape

5. Pod color 6. Pea color 7. Pea shape

each trait had two “character states”

DOM

REC

Gregor Mendel’s scientific work By transferring pollen collected from one plant to another he could cross plants with different traits and study the traits of offspring. His work was different from other investigators because he collected lots of observations and used math to identify the patterns, from which he proposed his Laws of Inheritance. •Law of Segregation •Law of Independent Assortment. Mendel, G., 1865, Versuche über Pflanzen-Hybriden) (Experiments on Plant Hybridization)

Mendel’s Laws of Inheritance He postulated that hereditary units or ‘factors’ (one dominant and one recessive) controlled traits; that during reproduction the factors separated into gametes…

1

gg g

2

Rg g

RR R

g

Rg

R

g

R

Rg R

g

Rg R

R

g

RR

Rg

g

R

•Law of Segregation; and that multiple traits sorted independently…. •Law of Independent Assortment.

R

3 3:1 g

Rg

gg

Because of this, in a single generation 7 traits produced 128 different hybrids! NOW THAT’S A SOURCE OF VARIATION!

Biochemistry, Cell Biology, Genetics, and Population Studies following the Turn of the Century

Chromosome theory

Thomas Hunt Morgan (1866 –1945) American geneticist and embryologist.

•Studied mutation in the fruit fly Drosophila melanogaster. •Demonstrated that genes are carried on chromosomes and are the mechanical basis of heredity (after Schneider, 1873). •These discoveries formed the basis of the modern science of genetics. crossing over

sex-linked traits

Population genetics

Ronald A. Fisher (1890 –1962) English statistician, evolutionary biologist, and geneticist.

•Developed many of the major methods used in statistics in the 1920’s (analysis of variance and maximum likelihood) •Applied statistical methods to study of population genetics. •Pioneered estimation of genetic linkage and gene frequencies by maximum likelihood methods

Sewall Wright (1889 –1988) American geneticist known for influential work on evolutionary theory.

Founder of theoretical population genetics (with R. A. Fisher and J.B.S. Haldane). Chief developer of mathematical theory of genetic drift, sometimes known as Sewall Wright effect, cumulative stochastic changes in gene frequencies that arise from random births, deaths, and Mendelian segregations in reproduction.

JBS Haldane (1892 –1964) British-born Indian geneticist and evolutionary biologist

One of the founders (with Fisher and Wright) of population genetics. His greatest contribution is found in ten papers on "A Mathematical Theory of Natural and Artificial Selection" - the major series of papers that quantified the analysis of natural selection.

DISCOVERY OF NUCLEIC ACIDS (DNA) Meischer (1869) ‘nuclein’

Watson (1953)

Crick Kossel (1890’s) ‘nucleic acids’

It took more than 80 years to unravel the nature of DNA!

Franklin Wilkin

The Central Dogma of Molecular Biology Supercoiled Supercoils RE U T UC R T S Double Helix E H T

{

CODON

T

P P P P

Purines

Guanine Adenine

Pyrimidines N

CO

DE

Ac i P O "Structural" "Silent"

A C G C T A A T C G G

i=repressor

G

P

N

OPERON

C G TA T A C G AC TG G TT A C TT A G

Deoxyribonuclei c Acid P

TH E

Cytocine Thymine

PROTEINS Cell walls Organelles ENZYMES Endonuclease Polymerase "Unwindase" Repressor

P

2)

C

1)

ENZYM

A a

ENZYM ENZYM

tRNA

mRNA

NUCLEUS

3)

PROTOPLASM

ribosome

POLYPEPTIDES NH 3

R

R R COOR R

R = AMINO ACIDS

ribosome

#1

E Supercoiled Supercoils UR T C RU T Double Helix ES H T Deoxyribonucleic Acid P

T

P P P P P

Purines

P

A C G G C T A A T C G G

ENZYM ENZYM

C

Guanine Adenine

Pyrimidines N N

REPLICATION

A a

m

Cytocine Thymine

NUCLEUS PROTOPLASM

GROWTH: “somatic”

m

mi

s i s to

i ti os

s

i ti os

s

#2

E

CODON

T

P P P P P

Purines

N N N N

Guanine Adenine

Pyrimidines N N

P

OPERON

C G TA G G T A C AC TG G TT A C TT A

Double Helix

E

CO

DE

Ac i P O "Structural" "Silent"

Deoxyribonucleic Acid P

TH

Supercoiled Supercoils

{

E TH

R ST

UR T UC

A C G G C T A A T C G G

i=repressor

TRANSCRIPTION

C

A a

ENZYM

Cytocine Thymine

NUCLEUS PROTOPLASM

MESSENGER RNA

Supercoiled Supercoils RE U T C U TR S Double Helix E H T

CODON

{

#3

T

P P P P P

Purines

P

i=repressor

VARIABILITY?

C

ENZYM

A a

Pyrimidines N

CO DE

Ac "Structural" "Silent" i P O

A C G G C T A A T C G G

Guanine Adenine

N

OPERON

C G TA G G TAC ACTG G TTACTT A

Deoxyribonucleic Acid P

TH E

Cytocine Thymine

tRNA

mRNA

NUCLEUS PROTEINS Cell walls Organelles ENZYMES Endonuclease Polymerase "Unwindase" Repressor

PROTOPLASM POLYPEPTIDES NH 3

R

R R COO R R

R = AMINO ACIDS

ribosome

ribosome

AA

SOURCES OF VARIATION CODON

OPERON

{

MUTATION

G T A C A C TG

changes in genetic code due to mutagens

TH E

G TT A

CG T A G CTT A

Ac i P O "Structural"

CO

"Silent" i=repressor

Mutagens = UV light, X-rays, chemicals, etc. (a) POINT mutations - one or a few nucleotides or codons (b) CHROMOSOMAL mutations during meiosis/mitosis •change in # of chromosomes fusion, fission •change in # or arrangement of genes on the chromosome: inversion, deletion, translocation, duplication Recombination

DE

SOURCES OF VARIATION

SEX

A a

A - dominant a - recessive

A A a

DIPLOID

2N

Alleles…

MEIOSIS

MITOSIS

A

A

DIPLOIiD DIPLOID

2N 2N

AAA

a

A a

a

a

a

A A A a A A a aa

A A

a

B B b

B B

B B

B b b B B B b b

b

a

a

b

b

a

b

AA Aa aa

gametes gametes

A a A AB B

A b Ab

a B a B

a a b b

BB Bb bb 2N

DIPLOID

N N

HAPLOID HAPLOID

SOURCES OF VARIATION

POPULATIONS

Gene Flow - migration of genotypes between populations can either maintain gene proportions, or change proportions of alleles, depending on sources of genetic material.

Genetic Drift - if gene flow and population size are SMALL, random shifts in gene frequency are more likely to be expressed in the population, and thus available for selection.

THE MODERN SYNTHESIS

George Gaylord Simpson (1902 –1984) American paleontologist; expert on extinct mammals and their intercontinental migrations.

Simpson was the most influential paleontologist of the twentieth century and a major participant in the Modern Synthesis, contributing Tempo and Mode in Evolution (1944). He is notable for anticipating such concepts as punctuated equilibrium (in 1944, see quantum evolution), and dispelling the myth that evolution of the horse was a linear process culminating in the modern Equus caballus.

Evolution of the Horse family

Anagenesis?

Correlated traits: increase in body size and tooth complexity; trend toward single toe (hoove).

Theodore Dobzhansky (1900 - 1975) noted geneticist and evolutionary biologist

One of the key authors of the modern evolutionary synthesis, he merged evolutionary biology with genetics in his book Genetics and the Origin of Species (1937), which among other things defined evolution as "a change in the frequency of an allele within a gene pool". Dobzhansky's work was instrumental in spreading the idea that mutations in genes provide the raw materials for natural selection.

Ernst Mayr (1904 - 2005) leading evolutionary biologist, renowned taxonomist, tropical explorer, ornithologist, historian of science, and naturalist.

His work contributed to the modern evolutionary synthesis of Mendelian genetics, systematics, and Darwinian evolution, the development of the biological species concept, and the concept of allopatric speciation.

Geographic isolation No gene flow with main population Rapid changes in small gene pool

By the end of the second World War….. NATURAL SELECTION PALEONTOLOGY

POPULATION GENETICS

THE MODERN SYNTHESIS …vindication of Darwinian Theory (80 yrs later)

RECENT ADVANCES IN EVOLUTIONARY THEORY •Patterns & Mechanisms of Speciation •Origin of higher taxa •Sources of variation

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•Advances in systematics

Evo-Devo role of regulatory genes

? - Meaning of Speciation Patterns Predicted B

A

Observed

Anagenesis in Trilobites

Anagenesis in Brachiopods measured by change in ornament through time

Definition of paleospecies?

Problems with gradualistic model? Predicted B

•Lack of intermediate forms •Arbitrary paleospecies definitions

A

Steven J Gould (1941-2002) Harvard paleontologist, evolutionary biologist, and historian of science.

Niles Eldredge (1943- ) American paleontologist, American Museum of Natural History

Eldredge, N. & Gould, S.J., 1972, Punctuated equilibria: an alternative to phyletic gradualism" p. 82-115..In Schopf, Thomas J. M. (1972). Models in paleobiology. San Francisco: Freeman, Cooper. ISBN 0877353255.

Pre-1970’s view of Paleontology: dominantly descriptive. Eldredge & Gould stimulated a new era, launching the field of PALEOBIOLOGY (along with the eponymous journal).

Speciation Patterns Predicted B

Observed D C

•Species stability •Rapid speciation A

A

B

Two major components of the Punctuated Equilibrium model:

Mode of evolutionary change Allopatric Tempo of evolutionary change Geologically instantaneous What does it predict about the pattern of evolution?

Stasis & Rapid Speciation

Stasis

sp. B

sp. C

Normalizing selection

Allopatric speciation Geographic isolation No gene flow with main population Rapid changes in small gene pool

sp. A

Punctuated Equilibria Pattern of stasis-rapid change-stasis Eldredge & Gould ‘72 argued that Punctuated Equilibrium model has greater explanatory power than the Darwinian gradualistic model of evolution.

•Statistical likelihood of preservation of subpopulations in fossil record?

Allopatric speciation

•Nature of the stratigraphic record

B

A

Missing section

Stratigraphic section

Stratigraphic gap = artifactual punctuation?

B2 B1 A4 A3 A2 A1

So, is the fossil record dominated by punctuated over gradualistic patterns?

BRANCHING PHYLOGENY EXHIBITS GRADUAL PHYLETIC EVOLUTION IN EOCENE MAMMAL LINEAGE

Gingerich, P.D., 1974, Stratigraphic record of Early Eocene Hyopsodus and the geometry of mammalian phylogeny, Nature 248, 107 - 109.

Punctuated Equilibrium Hypothesis is not the WHOLE STORY, but its development contributed to progress in evolutionary science. A. It provided testable predictions about patterns of evolutionary change. B. It offered a more nomothetic approach to the fossil record, initiating the Paleobiology Revolution. C. It offered an explanation for observations that seemed inconsistent with Darwinian gradualism (e.g., species stability). D. It illustrated the importance of ‘the collective’ (Paleobiology Database).

? - ORIGIN OF HIGHER TAXONOMIC GROUPS

©Benjamin Cummings Publ. 1979

The difference between clade and grade

MACROEVOLUTION

CAMBRIAN EXPLOSION Sudden appearance of all extant body plans, as well some completely novel plans never seen again. Total diversity far exceeding that of modern taxa.

©Natl. Geographic

©Natl. Geographic

DIVERSIFICATION

dogma But, how can Natura facit saltum? { Central Natural Selection Homeotic genes - code for body plans

STRUCTURES:

GENES:

ROLE OF INNOVATIONS BIOMINERALIZATION

Selection pressure related to the “arms race” created by origin of teeth, shell, limbs

BIOL SELEC

“Arms Race”

? - SOURCES OF VARIATION THE ROLE OF REGULATORY GENES The Biogenetic Law - E. Haeckel, late 1800’s “Ontogeny recapitulates phylogeny” HETEROCHRONY - changes in the onset of developmental stages in descendents relative to ancestors (Gould, 1977). Developmental type

Somatic Reproductive

Timing change in descendent

earlier Acceleration Progenesis

later Neoteny Hypermorphosis EVO-DEVO

Example: Human neoteny Map the change in skull shape...

©Sci. American. 1978

Notice that the juvenile chimp

…and see that Homo retains the ancestral juvenile form into adulthood.

©Benjamin Cummings Publ. 1979

has the anatomical shape of an upright biped.

? -EVIDENCE FOR COMMON ANCESTRY OF LIFE Phylogenetic Classification

Ernst Haeckel (1834-1919)

Cladistic Classification

Phylogeny based on biochemnical sequencing Galapagos Finches

Common ancestor

PHYLOGENETIC TAXONOMY OF 16S RIBOSOMAL RNA Woese, 1990

Paleozoic

Woese, 1967

Bacteria, Algae only for ~ 3 Byr

PHANEROZOIC

Mesozoic

PRECAMBRIAN

Cenozoic

ORIGIN OF THE GENETIC SYSTEM 3.8 Bya?

Conclusions •Darwin got it right, despite his limitations… •Understanding & misunderstanding of science •The nature of scientific discovery Strict adherence to scientific method? Strokes of brilliance or flights of fancy? •Peering through the veil…. •The story within the story behind the story…