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From Darwin to the Modern Synthesis


Did Erasmus Influence Charles Darwin? CD said no! ... Charles Darwin (1809-1882) Born in Shrewsbury, Shropshire, England, on 12 February 1809 ... – PowerPoint PPT presentation

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Title: From Darwin to the Modern Synthesis

Organic Evolution
  • From Darwin to the Modern Synthesis

  • 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?

Erasmus 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

  • 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

  • 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

  • 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
  • Differences among animals were driven by three
    different forces lust, hunger, and security

  • 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

  • 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

  • Did he anticipate the erroneous ideas of Lamarck?
  • Did Erasmus Influence Charles Darwin? CD said no!
  • CDs first edition of The Origin initially called

  • 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

  • Others Patrick Matthew (1790-1874), Edward
    Blythe (1810-1873), Charles Naudin (1815-1899),
    believed in natural selection

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Charles 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

  • 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

  • Guided by his cousin William Darwin Fox, an
  • 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
  • Also influenced by Adam Sedgwick, read Humboldt,
    graduated from Cambridge in 1831

The 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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  • 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
  • At the time, most geologists adhered to the
    catastrophist theory

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  • 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

  • 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

Natural Selection
  • Returned to England in 1836
  • Began recording his ideas about changeability of
    species in his Notebooks on the Transmutation of
  • 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

  • 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
  • Expanded in 1844 into a sketch of conclusions for
    his own use
  • These embodied the idea of natural selection

  • Typically cautious, he delayed publication of his
  • 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
  • Independently wealthy and never had to earn an

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  • A country gentleman among his gardens,
    conservatories, pigeons, and fowls
  • Practical knowledge in variation and
  • 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

  • Placed him at once among the front rank of
  • 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

Alfred 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

  • 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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  • 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

  • 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
  • Darwin spent the rest of his life expanding on
    different aspects of problems raised in the
  • 10 years after its publication most learned
    people had accepted it

  • Neither Darwin nor Wallace were present when the
    first public confrontation took place

Other 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
  • 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)

  • 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

  • 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

How Original was Charles Darwin?
The 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

Difficulties with Darwinism
  • Absence of transitional forms
  • Organs of extreme perfection
  • Evolution of instinct (behavior)
  • Hybrid sterility and interfertility of
  • Nature of variation
  • Orthogenesis
  • Lamarckism

Impact 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

  • 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
  • Natural selection was speculation, not science

Goldschmidt and hopeful monsters
  • Richard Goldschmidt (German-American, 1878-1958)
  • Understanding hereditary changes in
    development crucial to understanding evolution of
  • 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

  • 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

Modern 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

The Major Architects
  • 1930 R.A. Fisher The Genetical Theory of
    Natural Selection
  • 1931 S. Wright Evolution in Mendelian
  • 1932 J.B.S. Haldane The Causes of Evolution
  • 1937 T. Dobzhansky Genetics and the Origin of
  • 1942 J.S. Huxley The Modern Synthesis
  • 1942 E. Mayr Systematics and the Origin of
  • 1944 G.G. Simpson Tempo and Mode in Evolution

Ronald 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,
  • 1943 Professor of Genetics, Cambridge University

  • 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
  • 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

  • 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

Sewall Wright (1889-1988)
  • American mathematician and
  • First publication at 7 yo.
  • Interested in inbreeding (his parents
    were first cousins)
  • Specialized in small populations
  • For him genetic drift was crucial

  • 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

  • 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

John 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

  • 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

Theodosius Dobzhansky (Russian-American,
  • 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
  • Nothing in Biology Makes Sense Except in the
    Light of Evolution

  • 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

Julian 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

Ernst 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

  • 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)

George 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

  • 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

Major Contributions of the Modern Synthesis
  • Differentiation between Phenotype and Genotype
  • That there is not inheritance of acquired
  • 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

  • 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

  • There is continuous variation in phenotype,
    genes, and degree of reproductive isolation among
  • 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