Download Biol. 4974/5974 Lecture #2

Natural selection and the
modern synthesis
Evolution Biol 4974/5974
DF Tomback
Biol. 4974/5974
Lecture #2
M. W. Strickberger (2000) Evolution, Jones and Bartlett,
D. J. Futuyma (1998) Evolutionary Biology,
Sinauer Associates
Evolution and Natural Selection, and the
Development of the Modern Synthesis
“How extremely stupid not to have thought of that”
---Thomas Huxley
Both science and religion have resulted from humans
trying to figure out, “What’s it all about?”
Learning goals
Understand and be able to explain:
• How 18th and 19th century scientific discoveries and developments
paved the way for public acceptance of evolution.
• The evolutionary mechanisms proposed by Lamarck, why they
were a step forward in scientific thinking, and how they were
discredited.
• The mechanism of natural selection proposed by Darwin and
Wallace, and why it is a “statistical phenomenon.”
• Why natural selection was not immediately accepted when On the
Origin of Species was published, and even after Mendel’s Laws
were rediscovered.
• The origins of the modern evolutionary synthesis and its “official
beginning.”
• The impact of the evolutionary synthesis on the natural sciences
and related fields.
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Natural selection and the
modern synthesis
Evolution Biol 4974/5974
DF Tomback
Historical setting: timing
for a theory of evolution
 Darwin’s timing in history was excellent for
acceptance of the idea of evolution and a
“material” mechanism.
 During the 18th and 19th centuries, various
physical and natural sciences were
flourishing.
 Linnaeus began the system of binomial
classification (genus and species).
 Comparative anatomists such as Cuvier were
describing the similarities and differences
among species.
 The law of gravity was developed by Newton,
who had also discovered calculus.
 Van Leeuwenhoek discovered the world of
microorganisms after he built the first
microscope.
 Fossils of extinct animals placed in historical
sequence by geological strata (the first dinosaur
bone was found in 1677 but identified as reptilian in
1824 by William Buckland at Oxford).
 Principles of geological change over time by the
natural forces of slow erosion and deposition
(uniformitarianism) developed by Charles Lyell.
 Led to age of the earth reevaluated by different
methods, all resulting in ages greater than biblical
5,000 years.
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Natural selection and the
modern synthesis
Evolution Biol 4974/5974
DF Tomback
Dinosaurs even became part of “popular” culture!
Dinner in a dinosaur (Iguanodon), Crystal Palace (1852-1854)
P.W. Price (1996) Biological Evolution, Saunders College Publishing
These scientific developments challenged previously
held views that the world was unchanging
 By the early 19th century, the great age of earth, extinctions of
species, and evolutionary change were generally accepted
 During Darwin’s life, more discoveries were made, which
further supported his ideas about evolution
M.W. Strickberger (2000)
Mechanism of evolution
 By the early 19th century, evolution
was gaining acceptance, but how
evolution worked was unknown.
 Jean-Baptiste de Lamarck (17441829) proposed the first plausible
evolutionary mechanism.
 He suggested that species were
gradually modified over time,
offering a connection from strange,
extinct forms to contemporary
forms.
Lamarck
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Natural selection and the
modern synthesis
Evolution Biol 4974/5974
DF Tomback
D.J. Futuyma (1998)
Lamarckism
Change in organisms resulted
from some internal force
driving the organism towards
“perfection” or progress. This
was expressed as two “Laws”:
 The Principle of Use and Disuse
 The Inheritance of Acquired
Characters
National Geographic (1987) Field
Guide to the Birds of North America
Lamarckian evolution was formalized
as orthogenesis”:
It ascribed to evolution the drive towards
progress---ever greater perfection.
Cuvier (1769-1832) discredited Lamarckian
evolution with logical criticism:
 No intermediate forms
 Hybrids are always sterile
 Plants and lower animals have no
consciousness—how can they strive for
perfection?
At least Lamarck’s mechanism relied on
natural processes that accounted for
gradual change over time—a step forward
in thinking.
The recent discovery of stress-induced
mutagenesis in bacteria (“directed evolution”)
is not unlike Lamarckism.
M.W. Strickberger (2000)
Natural selection
D.J. Futuyma (1998)
In 1858, Charles Robert Darwin and Alfred Russel
Wallace published papers introducing natural
selection together in the Journal of the Linnaean
Society.
In 1859, Darwin published his detailed treatise on the
subject, On the Origin of Species.
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Natural selection and the
modern synthesis
Evolution Biol 4974/5974
DF Tomback
Summary of natural selection
 High reproductive rates in most organisms.
 Finite food and space limits numbers.
 Also, predation, parasitism, disease, competition,
climate.
 Variation among individuals.
 Certain variation results in higher survival and/or
better reproduction.
 Thus, relatively greater contribution of offspring
from some individuals.
 Their offspring may in turn have similar traits.
 Thus, certain “favored” variation spreads through
the species over time.
 Leads to “descent with modification” or evolution
over time.
Figure 11. Schematic of the main conceptual arguments for evolution by natural
selection given by Charles Darwin and Alfred Russel Wallace.
Evolutionary mechanism?
 The public was receptive to Darwin’s ideas.
 Evolution not doubted by most.
 Natural selection was difficult for some to
accept: Mechanism of inheritance not known.
(Mendel’s work was published in 1866 but
not widely read.)
 Between 1860 and the 1940’s scientists
agreed on evolution, but thought the
mechanism was some combination of natural
selection and Lamarckism.
 Here’s how Darwin’s ideas prevailed….
5
Natural selection and the
modern synthesis
Evolution Biol 4974/5974
DF Tomback
The biological revolution
 In the 19th century, biology was developing rapidly,
specializing, splitting into new fields, e.g.,
embryology, cytology, physiology.
 There were the experimental or lab-based biologists,
who worked on “systems.”
 There were the “whole organism” biologists, who
collected, described, observed, and compared--e.g.,
paleontologists, botanists, zoologists, systematists,
working in field, lab, and museum.
 Each group asked different questions; had different
perspectives, particularly regarding evolutionary
processes.
Rediscovery of Mendel’s Laws
 In 1900, Mendel’s laws were rediscovered, and genetics
became a field of science.
 Ironically, genetics caused a further rift: The naturalists were
evolutionists and studied natural populations.
 The new geneticists considered mutation as the major
mechanism of evolution; they did not see how natural selection
could change gene frequencies.
D.J. Futuyma (1998)
 They didn’t read each others’ work or cross-communicate;
multiple theories of evolutionary mechanisms flourished
Scientific isolation
 Meanwhile, new genetic advances supported gradual
evolutionary change, and mutationism fell out of
favor, but these ideas were not communicated
beyond genetics.
 Some naturalists and paleontologists still
subscribed to orthogenesis.
 “At the end of the 1920s, the situation in biology did
not seem at all promising for a meeting of the minds
in the near future.” –Mayr and Provine
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Natural selection and the
modern synthesis
Evolution Biol 4974/5974
DF Tomback
The “quiet synthesis”
 Despite hostility among disciplines during the first
30 years of the 20th century, the foundation for a
modern evolutionary synthesis was laid: abundant
evidence in support of natural selection.
 A few pioneers developed the ideas that later were
incorporated: Huxley, Ford, Haldane, Grinnell, and
Baur.
 The “bridge builders” were biologists willing to read
outside of their field.
 The synthesis occurred quietly, with enlightened
“new biologists” arriving at similar conclusions
about the mechanisms of evolution.
The birth of the
Modern Evolutionary Synthesis
 The official beginning:
 All participants agreed about the mechanisms of
evolution. There were few arguments and most over
small problems.
 No major revision has occurred since.
Some of the participants:
D.J. Futuyma (1998)
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Natural selection and the
modern synthesis
Evolution Biol 4974/5974
DF Tomback
D.J. Futuyma (1998)
There has been some “fine-tuning” of the modern
synthesis since the Princeton Conference.
Ernst Mayr
• Born July 5,
1904
• Died February
3, 2005
An astute naturalist and
arguably the most
important contributor to
the modern evolutionary
synthesis.
Stephen Jay Gould 1941-2002
•Brought the science of evolution to
the general reader through his
brilliant essays.
•Made contributions to our
understanding of the processes of
speciation and the relationship
between ontogeny and phylogeny.
•Introduced many terms to the field,
including “punctuated equilibrium.”
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Natural selection and the
modern synthesis
Evolution Biol 4974/5974
DF Tomback
The impact of the modern synthesis on science
 Was the modern synthesis a “scientific
revolution”? Yes and No.
 It was not drastically new—the seeds were
sown in 1859.
 But the impact on modern science has been
tremendous.
The impact of the modern evolutionary synthesis
 All branches of the natural sciences have been
influenced and organized by evolutionary
principles—known as the “first principles.”
 Also, the influence extends to geology,
paleontology, and anthropology, and now to
sociology, psychology, economics, and business!
 Researchers are looking at evolution and human
behavior.
The impact of the modern evolutionary synthesis on various disciplines
D.J. Futuyma (1998)
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Natural selection and the
modern synthesis
Evolution Biol 4974/5974
DF Tomback
Yet, public acceptance of human
evolution in the U.S. ranks near
bottom of 34 countries surveyed.
Why?
Miller et al. 2005. Public acceptance
of evolution. Science 313: 765-766.
Question asked: “Human
beings, as we know them,
developed from earlier species
of animals.”
Choices: definitely true,
probably true, probably false,
definitely false, did not know or
uncertain.
Only 14% of Americans chose
“definitely true”. “Probably
true” and “Not certain”
accounted for 55%.
Study questions
1.
2.
3.
4.
Why was Darwin’s timing very good for acceptance
of the idea that evolution had changed species?
What other discoveries had set the stage for
acceptance?
Explain the evolutionary mechanism known as
Lamarckism. What were the two fundamental
principles involved?
What were criticisms of Lamarckism? What was
the contribution of Lamarck?
Explain the basic process of natural selection as
presented by Darwin and Wallace?
Study questions, continued
5.
6.
7.
8.
9.
Was natural selection immediately accepted by
scientists as the primary evolutionary mechanism?
If not, what did people believe?
Did the rediscovery of Mendel’s laws unite
biologists? Why or why not?
How did some scientists become the “bridge
builders”? How did this set the stage for the
modern synthesis?
When was the official beginning of the modern
evolutionary synthesis?
What is the scientific impact of the modern
evolutionary synthesis?
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