Evolutionary Theory, Past and Present

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
}
•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…