Title: From Darwin to the Modern Synthesis
1Organic Evolution
- From Darwin to the Modern Synthesis
2Predecessors
- The idea of evolution had been around since the
times of the ancient Greeks - The problem was the explanatory mechanism, in
other words, how evolution works?
3Erasmus Darwin (1731-1802)
- One of the leading intellectuals of eighteenth
century England. Member of The Lunar Society - Remarkable array of interests and pursuits
- A respected physician, a well known poet,
philosopher, botanist, and naturalist
4- As a naturalist, he formulated one of the first
formal theories on evolution in Zoonomia, or, The
Laws of Organic Life (1794-1796) - This was a very popular book translated into
several languages, published 4 years before
Malthus' Essay on Population and 9 years before
Lamarck's published explanation on the theory of
use and disuse
5- He also presented his evolutionary ideas in
verse, in particular in the posthumously
published poem The Temple of Nature (1802) - Organic life beneath the shoreless waves
- Was born and nurs'd in ocean's pearly caves
- First forms minute, unseen by spheric glass,
- Move on the mud, or pierce the watery mass
- These, as successive generations bloom,
- New powers acquire and larger limbs assume
- Whence countless groups of vegetation spring,
- And breathing realms of fin and feet and wing
6- Believed the Earth was millions of years old
- Rejected the theory of special creation
- Discussed how life evolved from a single common
ancestor, forming one living filament - Believed in the inheritance of acquired
characters - Differences among animals were driven by three
different forces lust, hunger, and security
7- These forces, when interacting among themselves
and acting upon the Natural Variation of
individual in species improving, thus, the
different races (natural selection?) - Believed in spontaneous generation
- Some of his ideas on how evolution might occur
sound like Lamarckian, but actually it is the
other way around - Erasmus Darwin also wrote about how competition
and sexual selection could cause changes in
species The final course of this contest among
males seems to be, that the strongest and most
active animal should propagate the species which
should thus be improved
8- He used his observations of domesticated animals,
the behavior of wildlife, and he integrated his
vast knowledge of many different fields, such as
paleontology, biogeography, systematics,
embryology, and comparative anatomy
9- Did he anticipate the erroneous ideas of Lamarck?
- Did Erasmus Influence Charles Darwin? CD said no!
- CDs first edition of The Origin initially called
Zoonomia
10- Others like William Lawrence (1783-1867), James
C. Prichard (1786-1848), and William C. Wells
(1857-1917) did not believe in the inheritance of
acquired characters - They were physicians and could not find support
for it - They believed in selection, mutation, segregation
11- Others Patrick Matthew (1790-1874), Edward
Blythe (1810-1873), Charles Naudin (1815-1899),
believed in natural selection
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13Charles Darwin (1809-1882)
- Born in Shrewsbury, Shropshire, England, on 12
February 1809 - Grandson of Erasmus Darwin
- His father was a physician, wealthy
- Family high intellectuality, professional
ability, industriousness - Mother died when he was eight years old
14Education
- Brought up by his sister
- Graduated from the elite school at Shrewsbury in
1825 (Classics) - Sent to Edinburgh to study medicine. Dropped out
in 1827 (hated it) - Sent to University of Cambridge to study theology
in preparation for becoming a clergyman of the
Church of England - Loved to collect plants, insects, and geological
specimens
15- Guided by his cousin William Darwin Fox, an
entomologist - Scientific inclinations encouraged by his botany
professor, John Stevens Henslow - Henslow helped build Darwin's self-confidence
taught him to be a meticulous and painstaking
observer of natural phenomena and collector of
specimens - Also influenced by Adam Sedgwick, read Humboldt,
graduated from Cambridge in 1831
16The Voyage of the Beagle
- Henslow was instrumental in securing a place for
Darwin as an unpaid naturalist on the surveying
expedition of HMS Beagle to Patagonia (1831-6) - Heavy paternal opposition
- Under Captain Robert Fitzroy (an illegitimate
descendent of King Charles II) visited Tenerife,
the Cape Verde Is., Brazil, Montevideo, Tierra
del Fuego, Buenos Aires, Valparaiso, Chile, the
Galapagos, Tahiti, New Zealand, and Tasmania
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19- Opportunity to observe the various geological
formations found on different continents and
islands along the way, as well as a huge variety
of fossils and living organisms - In the Keelings he devised his theory of coral
reefs - At the time, most geologists adhered to the
catastrophist theory
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21- The catastrophist viewpoint was challenged by Sir
Charles Lyell in Principles of Geology (1830-33).
Lyell maintained that the Earth's surface is
undergoing constant change, the result of natural
forces operating uniformly over long periods - Read Charles Lyell
- Most impressed with the effect that natural
forces had on shaping the Earth's surface - Fossils in South America
22- Noted that certain fossils of supposedly extinct
species closely resembled living species in the
same geographical area - The Galápagos
- Observed that each island supported its own form
of tortoise, mockingbird, and finch closely
related but differed in structure and eating
habits from island to island
23Natural Selection
- Returned to England in 1836
- Began recording his ideas about changeability of
species in his Notebooks on the Transmutation of
Species - In 1838 read An Essay on Population (1798), by
the British economist Thomas Robert Malthus - Explained how human populations remain in
balance. Increase in the availability of food for
basic human survival could not match the
geometrical rate of population growth. The
latter, therefore, had to be checked by natural
limitations such as famine and disease, or by
social actions such as war
24- Darwin applied Thomas Malthus's argument to
animals and plants - By 1838 he had arrived at a sketch of a theory of
evolution through natural selection - In 1842 he drew up his observations in some short
notes - Expanded in 1844 into a sketch of conclusions for
his own use - These embodied the idea of natural selection
25- Typically cautious, he delayed publication of his
hypothesis - For the next two decades he worked on his theory
and other natural history projects - In 1839 he married his first cousin,
Emma Wedgwood (1808-96) - In 1842 moved to a small estate,
Down House, outside London - They had ten children, three of whom died in
infancy - Independently wealthy and never had to earn an
income
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27- A country gentleman among his gardens,
conservatories, pigeons, and fowls - Practical knowledge in variation and
interbreeding - He developed a friendship with
Sir Charles Lyell, became secretary
of the Geological Society (1838-41) - Continuous ill-health (suffered from
Chagas's disease?, Panic disorder?) - By 1846 he had published several works on the
geological and zoological discoveries of his
voyage
28- Placed him at once among the front rank of
scientists - Variability among barnacles
- Artificial selection
- Giraffe example
- Vestigial organs
- After five years of collecting the evidence, he
began to speculate on the problem of the origin
of species
29Alfred Russell Wallace (1823-1913)
- Natural history collector and explorer
- Also read Malthus. Wrote to Lyell
- Wrote to Darwin
- Wallace sent him a memoir on the
Malay Archipelago - Contained in essence the main ideas of theory of
natural selection - Lyell and Joseph Hooker persuaded Darwin to
submit a paper of his own read simultaneously
with Wallace's before the Linnean Society in 1858
30- Darwin then set to work to condense his vast mass
of notes, and put into shape his great work, The
Origin of Species by Means of Natural Selection,
published in 1859. 6 editions - Extremely readable book. First edition sold out
the first day! - Because of the food-supply the young born to any
species intensely compete for survival - The young that survive embody favorable natural
variations the process of natural selection and
these variations are passed on by heredity
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32- Therefore, each generation will improve
adaptively over the preceding generations, and
this gradual and continuous process is the source
of the evolution of species - Also introduced the concept that all related
organisms are descended from common ancestors - Provided additional support for the older concept
that the earth itself is not static but evolving
33Reaction
- Some biologists criticized Darwin's concept of
variation, arguing that he could explain neither
the origin of variations nor how they were passed
to succeeding generations - The most publicized attacks on Darwin's ideas
came from religious opponents - Seemed to place humanity on a plane with the
animals - Darwin spent the rest of his life expanding on
different aspects of problems raised in the
Origin - 10 years after its publication most learned
people had accepted it
34- Neither Darwin nor Wallace were present when the
first public confrontation took place
35Other Books by Charles Darwin
- The Fertilization of Orchids (1862)
- The Variation of Plants and Animals under
Domestication (1867) - The Descent of Man and Selection in Relation to
Sex (1871) - The Expression of Emotions in Man and Animals
(1872) - Insectivorous Plants (1875)
- The Effects of Cross and Self Fertilization in
the Vegetable Kingdom (1876) - Different Forms of Flowers in Plants of the Same
Species (1877) - The Formations of Vegetable Mould through the
Action of Worms (1881)
36- Darwin was elected to the Royal Society (1839)
and the French Academy of Sciences (1878) - He was also honored by burial in Westminster
Abbey after he died in Down, Kent, on 19 April
1882
37- Raised the idea of evolution from a hypothesis to
a verifiable theory - Thus, after Darwin, the following major cultural
revolutions had taken place in the human thought - 1. The Expansion of the Time-Scale
- 2. The Concept of a Changing Universe
- 3. The Elimination of Design
- 4. The Elimination of Miracles
- 5. The Inclusion of Humans within Nature
38How Original was Charles Darwin?
39The Eclipse of Darwinism
- Until 1875 Darwinism was hotly debated
- From then on, Darwinism fell out of favor among
many biologists - This was the result of many difficulties
40Difficulties with Darwinism
- Absence of transitional forms
- Organs of extreme perfection
- Evolution of instinct (behavior)
- Hybrid sterility and interfertility of
varieties - Nature of variation
- Orthogenesis
- Lamarckism
41Impact of Mendels Work
- Mendel himself rejected Darwins ideas
- Blending Inheritance (Mendels work was published
in 1865 but Darwin was unaware of it, as was the
rest of the world, until 1900) - Macro-Mutationism
42Further
- Mutation not necessarily adaptive
- Small variants among individuals and populations
not the same as differences among species - Selection may act on those variants but it takes
a different kind of mutation to generate new
species - Natural selection was speculation, not science
43Goldschmidt and hopeful monsters
- Richard Goldschmidt (German-American, 1878-1958)
- Understanding hereditary changes in
development crucial to understanding evolution of
morphology - Argued for important role of macromutation
- hopeful monsters
- Modern genetics refuted Goldschmidts arguments
but two key elements remain - Role of mutations of large effect
- Sudden transformations
- Genomic reorganization
44Orthogenesis
- The belief that evolution was directed by some
kind of undescribed force - That evolution had some sort of directionality
- Therefore, evolution of a species was influenced
most strongly by internal factors and was not
subject to the external forces of natural
selection
45Modern Synthesis
- Began in the 1930s
- Was the recognition that evolution as a synthetic
theory able to explain patterns of current and
past biological diversity and must propose a
mechanism (process) or series of processes, by
which these patterns can arise
46The Major Architects
- 1930 R.A. Fisher The Genetical Theory of
Natural Selection - 1931 S. Wright Evolution in Mendelian
populations - 1932 J.B.S. Haldane The Causes of Evolution
- 1937 T. Dobzhansky Genetics and the Origin of
Species - 1942 J.S. Huxley The Modern Synthesis
- 1942 E. Mayr Systematics and the Origin of
Species - 1944 G.G. Simpson Tempo and Mode in Evolution
47Ronald Aymer Fisher (British, 1890-1962)
- Mathematician by training
- He could not find a job, worked as
a farmer - His writing was difficult to read
- 1933 Chair of Eugenics at University College,
London - 1943 Professor of Genetics, Cambridge University
48- Fisher was a student at a time when there was
still controversy about Darwin's theories and
when Mendel's work on genes had just been
rediscovered - Made important discoveries in statistics (e.g.,
maximum likelihood), genetics, selection and
(genetic) dominance - It could be said that he invented a large part of
modern statistics
49- Fisher's models emphasized mass selection in
panmictic populations and tended to assume that
phenotypes results from many genes of small,
additive effect - This put him in direct conflict with the American
neo-Darwinian theorists such as Wright leading to
a famous public debate that lasted three decades
50Sewall Wright (1889-1988)
- American mathematician and
biologist - First publication at 7 yo.
- Interested in inbreeding (his parents
were first cousins) - Specialized in small populations
- For him genetic drift was crucial
51- As a statistician, Wright worked with covariant
analyses to determine the importance of various
factors in defining traits - This expertise was extended into animal breeding
- Mammalian genetics was one of his main interests
- Wright published on color inheritance in 1917 and
1918, the year in which he pioneered path
analyses in his study of body characteristics in
animals
52- He developed a theory that attributed a
substantial amount of genetic variance or
creativity to small genetic fluctuations among
small population groups - This was an innovative idea and caused the
well-documented debate with Fisher, who insisted
that variance could be analyzed only in relation
to large populations - Wright specialized in this field of population
genetics while a professor at the
University of Chicago
53John Burdon Sanderson Haldane(British, 1892-1964)
- One of the most influential scientists of the
20th. century, he studied relationships among
different disciplines and problems, including the
consequence of Mendelian genetics on evolutionary
theory, the relationship between enzymology and
genetics, and the application of mathematics and
statistics to the study of biology - He was a science popularizer
- Disillusioned with Marxism moved to India
54- He learned Mendelian genetics while still a boy
by breeding guinea pigs - In The Causes of Evolution he helped to marry
genetics to the older evolutionary theory - He reestablished natural selection as
the premier mechanism of evolution by
explaining it in terms of the
mathematical consequences of Mendelian
genetics
55Theodosius Dobzhansky (Russian-American,
1900-1975)
- Decided to become a biologist at 12
- Influenced by The Origin
- Migrated to the U.S. in 1927
- He defined evolution in his 1937 as A
change in the frequency of an allele in a gene
pool - Nothing in Biology Makes Sense Except in the
Light of Evolution
56- Dobzhansky's studies in population genetics
served as a basis for his explanation of how the
evolution of races and species could have come
about through adaptation - He discovered that successful species tend to
have a wide variety of genes that, while they do
not appear to be useful to the organism in its
present environment, do provide a species as a
whole with genetic diversity - This diversity enables the species to adapt
effectively to changes in the
surrounding environment
57Julian Huxley (British, 1887-1975)
- Humanist, atheist and science popularizer, Julian
Huxley, a Professor of Zoology, was the brother
of Aldous Huxley and grandson of Thomas H. Huxley - His research on hormones, developmental
processes, ornithology, and ethology influenced
the modern development of embryology,
classification, and studies of behavior
and evolution and led him to develop a
synthetic view of life
58Ernst Mayr (German-American, 1904-)
- Expeditions to New Guinea
- Worked at the AMNH (1932-1953)
- Harvard (from 1953 on)
- His career interests have spanned a remarkable
five different fields, including (1)
ornithology, (2) systematics, (3) zoogeography,
(4) evolutionary theory, and (5) philosophy and
history of science
59- Mayr developed the biological species concept,
population thinking in taxonomy, and the theory
of allopatric speciation - LIke the other neo-Darwinians, Mayr argued
against orthogenesis, neo-Lamarckism, and
saltationist versions of Mendelism - In the 60's and 70's Mayr defended evolutionary
taxonomy (which blended phylogenetic and
ecomorphological information to produce
qualitatively-justified classifications) - In the 70's Mayr's belief that the isolation of
small, peripheral populations led to rapid
speciation and morphological change
(i.e., the founder principle and
peripheral isolates speciation)
60George Gaylord Simpson (American, 1902-1984)
- Most influential paleontologist of the 20th
century the only major participant in the
Modern Synthesis to come from that field - Wrote hundreds of papers and books
- Leading expert on Mesozoic, Paleocene, and South
American mammals, plus penguins - Arguably the first paleontologist to make
consistent use of statistics, not just in alpha
taxonomy, but in paleoecology and in
macroevolution
61- In his 1944 book, Tempo and Mode in Evolution,
Simpson divided evolutionary change into tempo,
the rate of change, and mode, the manner or
pattern of change, with tempo being a basic
factor of mode - Simpson saw paleontology revealing the long
history of life on earth, as a unique field
through which to study the history of evolution
62Major Contributions of the Modern Synthesis
- Differentiation between Phenotype and Genotype
- That there is not inheritance of acquired
characteristics - Genes are the basis of inheritance and there is
not blending inheritance - Genes mutate and that is the source of variation
- Mutation is undirected
- Evolutionary change is a populational process
- Change in gene frequencies within populations can
occur via Drift or Selection
63- Even slight intensity of selection can result in
substantial evolutionary change over a short time - Selection can alter populations beyond the
original range of variation - Natural populations are genetically variable
- Populations differ geographically and these
differences have a genetic basis - Natural selection occurs in current populations
- Differences among populations are often adaptive
- Species represent different gene pools are
defined by genetically based reproductive
isolation
64- There is continuous variation in phenotype,
genes, and degree of reproductive isolation among
populations - Higher taxa arise through the accumulation of
small differences (i.e., the processes that drive
divergence among populations are the same as
those that lead to higher taxa) - Gaps in the fossil record are explained by the
incompleteness of the fossil record - Observations in the fossil record are consistent
with all of the above principles of evolutionary
change