Transcript Document

History of Evolutionary Thought

I. Early Ideas of Change
– the Greeks

II. Darwinian Revolution
– Intellectual environment pre-Darwin Change as
a concept Darwin and contemporaries

III. Post Darwin
– Blending Inheritance Mendel Biometrics

IV. The Modern Synthesis
– Hardy-Weinberg Dobzhansky Haldane, Fisher,
Wright Recent innovations
I. Early Ideas of Change
A. Anaximander -- 6th Century BC
"Men first formed as fishes;
eventually they cast off their fish
skins and took up life on dry land."
B. Xenophanes -- 6th Century BC
recognized that fossils are the
remains of organisms that once lived
I. Early Ideas of Change
C. Empedocles -- 5th Century BC –
the father of the evolutionary idea

plants and subsequently animals rose from the
earth

they arose as unattached organs and parts that
joined together in haphazard fashion. Most
conglomerates were freaks and monsters
incapable of living, but occasionally a combination
of organs appeared which could function as a
successful living organism. These survived and
reproduced.
I. Early Ideas of Change
C. Empedocles Con’t.
– This bears elements that are still
accepted, the first glimmerings of
"survival of the fittest"
– included man in his ideas of formation
I. Early Ideas of Change
D. Aristotle -- 4th Century BC -- bit of a step
back
 maintained complete gradation in nature
 lowest stage is inorganic
 organic beings arise from inorganic by
direct metamorphosis
 (spontaneous generation, eg, flies from
meat)
D. Aristotle -- 4th Century BC
first known organization of
life, first tree of life
although without limbs
Thinking then stood still for about 2000
yrs, most of the ancient Greeks
forgotten, Christian belief of special
creation dominated
II) DARWINIAN REVOLUTION

The intellectual environment in
the 1600-1700's

Change as general concept
DARWINIAN REVOLUTION Con’t:
Plato and the "essence”
– Plato incorporated into Christian ideas
– the essence is the thing -- that which
we have is not the true, but a reflection
of the essence, VARIATION WAS
MEANINGLESS the mean or the typical
was the object
– the "essence" exists in the mind of god
– Extinction not possible, because
extinction would be imperfect
DARWINIAN REVOLUTION
Scala Naturae (the great chain of being)

Order is superior to disorder, complete
gradation throughout life, without gaps,
this translated into human society

to change the Order of life is unthinkable

the role of science was to catalogue the
ladder, describe the adaptations by which
organisms are so wonderfully suited to
their functions ad majorem Dei gloriam (for
the greater glory of God) (All of Linnaeus'
work)
DARWINIAN REVOLUTION Con’t:
Change as general Concept

The Geologists
– Around the late 1700's, due to influence of
astronomers, geologists began to question
whether the earth was static (Catastrophism =
creation.....flood......re-creation) or changing.
– Sedimentary rocks
• recognized that they had been laid down at different
times
• Buffon (1779) suggested the world might be 168,000 yrs
old!!! (Bishop of Usher mid 1800's declared the world
created in 4004 BC)
Buffon

In 1753 raised the possibility that
closely related species had developed
from a common ancestor.

1766 all related organisms shared the
same internal mold.
DARWINIAN REVOLUTION Con’t:
Change as general concept
James Hutton (1788) - UNIFORMITARIANISM
– "same process responsible for both past and present
events"
– implied very old age of earth, with "no vestige of a
beginning -- no prospect of an end"

Charles Lyell (1830-1833) - Principles of Geology
– Championed Uniformitarianism, but held a steady
state view that could not admit biological evolution
DARWINIAN REVOLUTION Con’t:
Change as general concept

Jean-Baptiste Lamarck (1744-1829)
– Philosophie Zoologique (1809)
– Most important evolutionist (or "transformist")
pre-Darwin
– Lineages persist indefinitely (ie, no such thing
as extinction) but forms change from one into
another. Lamarck's tree of life was unbranching
DARWINIAN REVOLUTION Con’t:
Lamarck…..(pre-Darwin)

Fossils were viewed as forms that had changed into
something new, these were left from previous time

"Great alterations in the environment of animals lead
to great alterations in their needs, and these
alterations in their needs necessarily lead to others
in their activities. Now if the new needs become
permanent, the animals then adopt new habits which
last as long as the needs that evoked them.
DARWINIAN REVOLUTION Con’t:
Lamarck…..(pre-Darwin)

Primary mechanism of change was "internal forces",
an unspecified striving that caused individuals to
produce offspring slightly different than themselves.

Nervous fluid

Inheritance of acquired characters, probably less
important to Lamarck, was his downfall. Believed that
through use, individuals modified their phenotype,
these transformations would then be transmitted to
offspring, and the whole lineage would transform
through time. GIRAFFE EXAMPLE.
DARWINIAN REVOLUTION Con’t:
Lamarck…..(pre-Darwin)

Rather uncharismatic, clashed severely with
GEORGES CUVIER, famous French
anatomist, who championed the idea of fixity
of species (eventually established that forms
do go extinct). Cuvier believed that each
species has a separate origin, is constant in
form, then goes extinct. Essentially kept
Lamarck from becoming popular in France.
DARWINIAN REVOLUTION Con’t:
CHARLES DARWIN (1809-1882)
DARWINIAN REVOLUTION Con’t:
CHARLES DARWIN (1809-1882)

One of the most biographied, and storied
scientist ever, some of which make great reading.

A very wealthy family, child of 1st cousins, Sent
to the best schools and highly educated.

From a family of educated people (Erasmus
Darwin, Grandad, early transformationist thinker,
poet, naturalist and physician). Went to
Cambridge to study theology, then back to
become physician, but spent most of his time
shooting, collecting beetles
DARWINIAN REVOLUTION Con’t:
CHARLES DARWIN (1809-1882)

palled around with J. S. Henslow, Botany prof at
Cambridge, who got him on board the HMS
Beagle as ship naturalist. Spent 5 yrs touring
through South America, Galapagos collecting and
describing.

This voyage often pointed to as convincing him
of evolution, but in truth, his realizations came
after return. He had seen much and it certainly
prepared him to change his ideas, but the actual
events came after his return to England in 1836
DARWINIAN REVOLUTION Con’t:
CHARLES DARWIN (1809-1882)

One of the first events was the
identification of Galapagos mockingbirds
(not finches) as different species on each
island. He had noted resemblance to
mainland forms, but this identification by
John Gould caused him to doubt the fixity
of species.
DARWINIAN REVOLUTION Con’t:
CHARLES DARWIN (1809-1882)

He still had no concept of a mechanism, that which
he is now famous for.

The key event appears to be the reading of
Malthus' (1798) Essay on the Principle of
Population which argued that unchecked growth
would lead to famine and destruction of the human
race.
– In his autobiography "I happened to read for amusement
Malthus on Population, and being well prepared to
appreciate the struggle for existence which everywhere
goes on from long-continued observation of the habits of
animal and plants, it at once struck me that under these
circumstances favorable variations would tend to be
preserved and unfavorable ones to be destroyed."
DARWINIAN REVOLUTION Con’t:
CHARLES DARWIN (1809-1882)

This was the key element to his theory of
modification by descent. He sat on it for
another 20 yrs, publishing monumental
works on worms, molds, orchids, etc. but
only in 1856 started writing his "big book".

Artificial selection by breeders, especially
pigeons and cattle could produce almost
any form, basic concept was the same as
his idea of preservation of favorable
variations
DARWINIAN REVOLUTION Con’t:
Alfred Russell Wallace (1823-1913)

Absolute opposite of Darwin. Grew up in large
family, father died, very poor, but was a rabid
naturalist. He traveled primarily in Malaysia,
Amazonia, and financed trips through collecting
and selling specimens to wealthy Brit. collectors.
Spent his whole life in and out of financial ruin (eg,
one boat burned on way back from Amazonia with
7 yrs of collections)

Simultaneously arrived at natural selection as a
process (1858) during a malarial fever delirium in
Indonesia. The vision came to him, he wrote it
down (after getting stronger) in a few pages and
sent it to Darwin to review .
DARWINIAN REVOLUTION Con’t:

Darwin sent this and abstracts of his own
work to Charles Lyell and his friend Joseph
Hooker who urged him to present the
manuscripts to the Linnaean Society of
London. He did, they received little
reaction, but then he published an abstract
of his ideas in 1859
"The Origin of Species by Means of Natural
Selection, or the Preservation of Favoured
Races in the Struggle for Life"
DARWINIAN REVOLUTION Con’t:
Two Basic Tenets (in Origin…)

all organisms descended with
modification from common ancestors

chief agent of modification is natural
selection on variation. This was the first
tree of life with branches, the first with a
precise mechanism, and the first to
emphasize variation as elemental
DARWINIAN REVOLUTION Con’t:
The influence of Malthus:

read by both Darwin and Wallace

emphasized exponential growth in
populations
DARWINIAN REVOLUTION Con’t:
Ex. of Exponential Growth and Its
Potential Role in Selection…

Wallace: 1 pair birds produces 4 young per
year
– each pair produce 4 times in a life
– 15 years each pair produces 10 million birds

Darwin: Elephant lives 100 yrs, produces
about 6 progeny between 30-90
– 1 pr produces 19 million in 750 yrs if all offsp.
reproduce
DARWINIAN REVOLUTION Con’t:
Brodie: 2 Bullfrogs-----50,000 eggs/life (frog = .5 lb; egg
mass=25 cm2)
if 10 survive (.02%)...........250,000 eggs
if .02% surv. (50 frogs).......1,250,100 eggs
250 frogs.......6,250,000 eggs (4th generation)
by 10th gen. 19,531,250......~500 billion eggs
which is about 2 sq km of egs and about 10,000 (9,866
tons) of frog
DARWINIAN REVOLUTION Con’t:
Natural Selection

4 elements as described by Darwin and Wallace
– Variation
– Over reproduction
– Some variations advantageous, some
deleterious
– Individuals with advantageous variations
leave more offspring than others, thus give
rise to next generation
DARWINIAN REVOLUTION Con’t:
Natural Selection (by Darwin and Wallace)
Did not incorporate any element of
inheritance, taken for granted that
parents produce like offspring
DARWINIAN REVOLUTION Con’t:
Afterwards.....

Darwin became an invalid and a recluse, never got
used to the criticism but continued to write. Took
every criticism of his theories to heart. Did not
completely abandon his Deism until death of his
daughter at about age 5.

Wallace continued to travel and collect, always
had the utmost respect for Darwin, and tended to
give him all the credit (Wallace's version had only
one example, Darwin's literally thousands),
Became increasingly interested in the occult and
eventually wrote on mysticism and traveled the
world attending séances......
III. Post Darwin (Blending Inheritance)

Most biologist of Darwin's day accepted
BLENDING INHERITANCE, assuming that
the stuff of inheritance was some sort of
fluid, which when mixed together produced
an average between parents.

Fleeming Jenkin, critic of Darwin, pointed
out that selection could not sort out a
superior liquid from a mixture, one of the
most damning criticisms.
Post Darwin
B. Mendelian inheritance

Gregor Mendel (Czech Monk) performed
experiments demonstrating particulate
inheritance in mid 1800's but they were
unknown until "rediscovered" by De Vries
and Tschermak

Initially a great blow, because characters
that are controlled by one or a few loci
exhibit discrete variation -- differences
between genotypes was too big to fit into
Darwin's theory
Post Darwin
Biometricians

Karl Pearson, August Weismann,
Francis Galton were demonstrating
that most genes have only small
effect, and that most variation is
continuous
– (eg, body size, speed, vs eye color) this
fit fine into Darwinian theory
The MODERN SYNTHESIS

Again around the 1930's, Natural Selection
and gradual evolution started to come back
into vogue, primarily through the efforts of
a few geneticists responsible for what is
now called the New Synthesis or NeoDarwinian theory.

Primarily combines genetics, mathematics
and evolutionary theory into a set of ideas
called population genetics
The MODERN SYNTHESIS
Hardy-Weinberg (-Castle) theorem

A demonstration that frequencies of genes
do not change from one generation to the
next if all members mate at random and
there is no advantage to any gene. This is
the foundation of all population genetics,
because by adding terms for selection and
migration, it can be shown that gene
frequencies do change in the face of very
weak forces.
The MODERN SYNTHESIS
Theodosius Dobzhansky (1900-1975)

With fruitflies, revealed hidden genetic variation
and demonstrated that the differences between
races and species were genetic --- led to the
understanding that species are not "morphotypes" but variable populations that are
reproductively isolated from one another

One of the main fathers of the New Synthesis, by
combining genetics with the more established
views of evolutionary process
The MODERN SYNTHESIS
Other Major Players

JBS Haldane: drinker, brawler, and theoretician

famous quotes:
“the creator had an inordinate fondness for
beetles"
"I would not save a man from drowning, but I
would save 2 brothers, or eight cousins" (in
reference to average relatedness)
The MODERN SYNTHESIS
Other Major Players

Sewall Wright: used Guinea pig as eraser, worked
on polydactyly and coat color in guinea pigs,
intimidating mathematician, pioneer in multivariate
approaches to evolution, Shifting balance theory
of maintenance of variation

R. A. Fisher: competing mathematician and father
of linear statistics (Regression); "The Genetical
Theory of Natural Selection"
Tenets of the Synthesis

See Page 26-27 in Futuyma
Recent Challenges or Innovations

Cladistics -- Willi Hennig, a new and more
rigorous means of approaching questions
of relationship founded on a specific model
of evolution including parsimony

Neutral Theory -- Mootoo Kimura,
suggested that most evolution is neutral
and has no effect on the phenotype, based
on the idea that most DNA does nothing
Recent Challenges or Innovations

Punctuated equilibrium -- Stephen Jay
Gould & Niles Eldridge, later Stephen
Stanley; motivated by observation that
fossil record tends to reflect a less
continuous change than expected by
gradual change. Referred to by some as
evolution by jerks. Non-constant mode and
rate of evolution, at times suggested that
most evolutionary change occurs at level
of species-selection
Recent Challenges or Innovations

Group selection -- Wynne-Edwards,
Rensch, rescued by Wilson, Wade:
units other than the individual are the
unit of selection and evolutionary
change