the same phenomenon is sought again, preferably by independent
investigation, and the interpretation given it confirmed or discarded by means of novel
analysis and experimentation.
scientists attempt to abstract the information into the form that is simplest,
most easily recalled, and most esthetically pleasing--the combination called elegance--
while yielding the largest amount of information with the least amount of effort.
a parsimonious explanation is the one that
requires the fewest ad hoc assumptions and when two theories are equally good in
explaining a particular set of phenomena, the one that is more parsimonious is favored.
if something can be properly measured, using universally accepted scales,
generalizations about it will be rendered less ambiguous.
the best science stimulates further discovery, often in unpredictable new
directions, whose content confirms or modifies the parent formulation.
there must exist a way in which a scientific concepts (theories) can be
shown to be wrong.
“scientific revolutions” and /or
If entirely new facts emerge, entirely
new concepts will likely be needed to accommodate them. This may lead to sudden and
dramatic, changes in concepts
This represented a paradigm shift from the Ptolemaic model of heavens (earth at center of the
universe) to the heliocentric model (sun at the center of solar system)
1. Religion/Theology--invoke the supernatural, revelation, authority
2. Philosophy--logic from first assumptions (truth, justice, morality)
3. Science--natural processes, observations, order (rational, materialistic, testable)
Archbishop Ussher (1581-1656) (wall chart of world history)
Applies a SCIENTIFIC (rational, natural) approach to the problem of the age of the earth. If
human history equals earth history, we can reconstruct the earth’s time scale using written
Ussher used biblical & other documents to establish age of earth:earth’s birthday: Oct. 22,
-Supplement the revealed theology of the Bible.
-Identify the perfection, the order and harmony of nature as evidence for God’s design.
the term “fossil” was applied to anything (including minerals) found in the earth. Those
objects that we today recognize as once living organisms were thought to represent not
natural, but represent supernatural objects placed in the earth by the devil or some other
supernatural being either as symbols of some living objects or as representations of nonliving
fossils are found in rx. How do they get inside rx? Rx were thought to be permanent.
fossils are rare, organisms are not
most fossil represent extinct species (>>99%), so one cannot find modern organisms that
look the same.
living organisms are made of flesh and bone; fossil almost never preserve flesh, so one
must know anatomy well in order to see similarity between fossil and organisms.
fossil are often distorted, broken by preservation: don’t look anything like an organism
explaining how sedimentary rocks form. Important
breakthrough--rocks are no longer seen as permanent!
Steno showed that solid rock can form (sedimentation, compaction) and be destroyed
But he saw this as a unidirectional (times’ arrow) process.
he accepted the biblical chronology),
James Hutton (1726-1797): earth as an inexhaustible heat engine
as a deist, believes in harmony of the universe, a “designer”, and a purpose. (teleology)
describes rock cycle, explains how rocks can be “rejuvenated” REJUVENATION
Hutton’s world view leads him to claim that earth is “pure cycle”, time’s arrow cannot be
deciphered and therefore, although the earth has a history, it consists of nothing more than
exactly repeatable cycles. studied soil on his property and how it went away
‘no vestige of a beginning, no prospect of an
a 17th/18th Century world view about Gods relationship nature. God created the
physical universe and the laws that govern it, and these laws then produced what exists and
continue to produce what will come next. In this scheme, God doesn’t need to hang around to
supervise; the laws will take care of everything.
1. The Divine is held to be the first cause of the world.
2. Deism distinguishes the world and the Divine as effect and cause.
3. “God is apart from the creation which He brought into being, and unconcerned as to the details
of its working. Having made Nature, He allows it to run its own course without
interference on His part.”
4. Deist rely solely on nature, scripture (revealed theology) is of no importance.
5. Belief in theorderliness of the universe—a very mechanistic view of the world
TELEOLOGY—The PURPOSE (nature is a purposeful place):
--rejuvenation of earth’s surface isnecessary according to his world-view
--processes are cyclical (time’s cycle), in fact, perfectly so, such that when we go from
the same part of one cycle to the same part of another cycle we cannot tell them apart and
so time is indecipherable, indeterminate:
an ultimate goal/purpose (teleology)—the earth was designed this way to
support human needs, as they saw it.
no vestige of a beginning, no prospect of an end”
this is NOT a claim that the earth is of INFINITE age, it is a claim that because of how it
works mechanistically, we cannot tell how old it is.
Unconformity at Jedburgh
The lower layers are tilted almost vertically,
and above an intervening layer lie horizontal
It states that if we are to understand past phenomena, we must accept that there
are certain laws and processes of nature that are time invariant (do not change with time). That
means that we can study those laws and processes today using experiments and observations and
invoke them in the past—“the present is the key to the past”.
Charles Lyell (1797-1875)
Uniformitarianism: “present as the key to the past”+ gradualism
“Principles of Geology” (1830-1833)
near constant (average) state
of the earth (gradualism). The latter does not imply that the earth was static and unchanging, but
rather that changes in one part of the earth were either balanced by opposite changes elsewhere
the notion that changes occurred in the past at the same rates as
they do today, and that those changes were cyclical, i.e., they always returned you back to the
same state (ala Hutton).
Extinctions simply did not fit with
the “harmony’ of the universe and the perfect “design” they envisaged.
when rock layers are ordered from bottom to top, particular types (species) of fossils are
found in only one part of stratigraphic column (particular layers)
•each fossil type has a first appearance (origin), and a last appearance (extinction).
•since according to Steno, rock lower in the sequences are older than those higher in the
sequence, the sequence of fossils likewise can be ordered into a TEMPORAL sequence.
•this sequence can be used to construct a relative TIME SCALE
One explanation was that the fossils represented organisms that had yet to be discovered by
naturalists: they were living out there somewhere, but had not yet been found. Another
explanation was that fossils represented organisms that were no longer around, i.e., they were
founder of Comparative Anatomy
“Proof” of extinction”
1. examines wooly mammoth
2. compares IN DETAIL to modern elephants
3. finds differences between mammoth and modern elephants to be greater than differences
between modern species of elephants, therefore mammoth is a distinct species.
4. the idea something the size of a mammoth is yet be discovered alive, can be rejected, therefore
concludes that mammoth MUST be EXTINCT species.
In order to do the above, Cuvier had to be able to compare IN DETAIL fossils to living
organisms. To do this he had to acquire knowledge of ANATOMY of many types of organisms
(not just human anatomy). He is thus recognized as the founder of Comparative Anatomy.
believed that there was a single creation of all species and that through geologic time some of the
original species became extinct during catastrophic events.
CONSEQUENCES of the reality of extinctions:
1. Biology: Uniformity of state CANNOT be correct-->the biological state of the earth has
changed through time. That is, there is a “time’s arrow” in the organic composition of the earth
2. Use fossils for dating rock layers (late 1700’s, early 1800’s) establishment of GEOLOGICAL
TIMES SCALE (early to late 1800’s)
Jean Baptiste Lamarck
laws ofUse and Disuse and the
Inheritance of Acquired Characteristics
Imagine a giraffe having to reach ever
higher to get food during its life. This continued
reaching would stretch its neck, such that although it
came from parents with a shorter neck, during its life
its neck got a little longer than the neck of its
Inheritance of Acquired Characteristics
Lamarck argued that the traits modified
through uses and disuse are passed from parent to
offspring and thus a species can undergo change. In
fact, he viewed the extinctions that Cuvier had
demonstrated not as a complete disappearance of a
species, but rather as a transmutation of an ancient
species to a new one
Lamarck’s ideas were well-known but were rejected almost immediately, mainly because there
was no empirical data (observations) to support it. In fact, Lamarck was made fun of by Cuvier
who described him as someone who believed that if you bring “a hen near water it will become a
Charles Darwin (1809-1882)
On the Origin of Species by Means of Natural Selection
(lyell was his intellectual hero)
5-year voyage on the research vessel,Beagle in 1831-1836,
started with tortoises and curiosity of why one species lived on one island
next looked at birds and their little differences which led to immutability of species
Saw difference in the beaks of the finches
Birds with different beaks fed on different food (13 TOTAL)
Descent with Modification
has occurred by branching (different species
share common ancestral species)—
Evolution (what Darwin more descriptively called "Descent with Modification") embodies 2
A. Change within a lineage (Modification = Anagenesis)
Branching (different species share ancestors:Descent =
The totalnumber of species on oceanic islands is small compared to the number on an
equal area of continent, but the proportion ofendemic species is very high
•Oceanic islands are missing entire Classes: Terrestrial mammals are not found on any
island >300 miles from mainland. but arial mammals (bats) are found on such islands,
and many of these are endemic.
Endemic species often possess characters that are adaptiveelsewhere, but are useless
characterson the island (wings of flightless birds)
•Endemic species often show (new) adaptive traits not possessed by any of their relatives
•"The most striking and important fact" (p. 397) is the affinity of these island species to
those of the nearestmainland, without being actually the same species
Within anarchipelago, species are more closely related to each other than to those on the
mainland (but still distinct from each other). The principle applies widely that island
inhabitants are most closely related to the inhabitants of a region from which
colonizationis possible. According to this principle, it must be the case that at some
former time,a single parental species covered both ranges
How to explain similarity in
Homology-- similarity of
underlying structure shared by
organisms that are doingtotally
different things: topology vs.
function of tetrapod limbs
bones are not identical, they have
been modified as a result of
millions of years of evolution. The
degree of similarity in basic
structure is so great, however, that
it is difficultnot to conclude that it
reflects common ancestry rather
than independent origins.
The early stages of development are the same (or similar) in organisms that are very
different from each other as adults. This is so because the organisms shared a common
ancestor that had those early stages stages. Through the process of descent with
modification, the later stages of development in diverged from each other.
There is usually a difference in form between embryo and adult.
•Serial structures (e.g., segments, limbs) are usually identical in the embryo, but specialized and
diverged in the adult.
•Different species often have very similar embryos, even if the adult forms are quite different.
Vestigial (rudimentary) Organs
They served a purpose in an ancestor that had a different life habit. They are retained because
they are not “maladaptive” (they do not reduce fitness; they are adaptively neutral) and therefore
they are not eliminated quickly.
Individuals of the same species differ from each other -- (Fact) (look around
the classroom). Origin of variability is random (Darwin knew little of how this works, but
he argued it was random)
Many of these differences are heritable -- (Fact) (think about features that you
may have inherited from your parents).
Some individuals do not survive to reproduce, elimination of individuals is nonrandom
– “better” survive, leaving more offspring, this will lead to change in population
organic change through time. (deduction not fact)
which claimed that the intrinsic rate of
growth of human populations exceeds the rate of growth in food supply and this leads to
competition for those resources. A “balance” is reached, but this can only happen if not all the
offspring reach adulthood.
Malthus’ Iron Laws of Population
Law 1: Food Supply grows in a linear fashion (arithmetically)
• Law 2: Populations tends to increase exponentially
Deduction 1: Populations always tend to outrun food supplies
Deduction 2: More offspring born than can survive
Deduction 3: Will always be competition for food (= resources)
Those that survive have some advantage over
those that die, so those advantageous traits will become more frequent in the population than the
if the traits are heritable, the
advantageous traits will continue to accumulate from one generation to the next.
Natural Selection is quite different from mechanisms proposed before, such as Lamackism. In
natural selection, it is not individuals that evolve, but populations.
small, incremental changes between generations. To Darwin, continued, gradual
accumulation of such small changes could lead to large changes over many generations
the mutations are random
Darwin argued that if selective breeding by
humans can produce the huge varieties of dogs and pigeons in just centuries, Natural Selection
operating more slowly but having 1000 to 100000 times more time could lead to the diversity of
Mechanism of Inheritance
Darwin and the fossil record
Life of the Pre-Cambrian
Age of the Earth:
Mechanism of Inheritance
Theoretically, this blending was a smooth spectrum of infinite possible outcomes like with paint,
where two with still other colors. If this was how heredity worked, new genetic variations would
quickly be diluted out of a population. They could not accumulate as the theory of evolution
required. evolution and natural selection needed time to prove true (and thats why blending is incorrect) darwins biggest problem
Gregor Mendel (1822-1884)
Discovered the laws of heredity but his work did not become known
until the 20th century.
Mendel crossed a
round with a wrinkled seed plant and in
the next generation got plants that
produced round seeds plant. Obviously,
this result was alone enough to refute
Gregor Mendel (1822-1884)
Discovered the laws of heredity but his work did not become known
until the 20th century.
When he crossed individuals from the F1
generation with each other (all roundseed
producers), in the subsequent
generation (F2) he got some plants that
produced round seeds and some wrinkled
seeds. The ratio of round to wrinkled
plants was 3 to 1.
Fundamental Laws of
1. Dominant vs. recessive traits.
2. Inheritance is particulate (not
3. Information about characters carried
4. Two copies of a “gene” carried for
each trait -- one from each parent
5. Law of segregation: genes segregate
during gamete formation (1/2
gametes carry one allele (gene), 1/2 carry other).
6. Law of independent assortment: genes for different traits are inherited independently of one
another (true for genes carried on different chromosomes).
genetic composition of individual.
appearance of individual.
alternative forms of same gene
organisms whose chromosomes come in pairs.
pairs of chromosomes with same genes in same order.
two homologous chromosomes with the same/different allele.
Inheritance isNot blending (half from each parent) -- that would lead to Dilution.
Inheritance ofAcquired Characters does not work -- what is acquired during an individual’s
life isNot passed on to the next generation (Lamarckian evolution, increase in length of giraffe’s
neck due to stretching).
Darwin and the fossil record
Problem: Where are all the “transitional” forms?
If species A evolves into species B, as Darwin claimed, shouldn’t we seeAll the intermediates?
Darwin attempted to address this by invoking theincompleteness of the fossil record.
he argued that it would be
unrealistic to expect to see many intermediates in the fossil record because we only have 1 percent of fossils
Problem: Life of the Pre-Cambrian
So why were these ancestors of
the varied Cambrian forms not being recovered?
As with the previous problem, Darwin invoked the incompleteness of the geological record as an
Problem: Age of the Earth
Darwin’s theory required that the earth be very old—anything shorter than a billion years would
not provide sufficient time for life on earth to evolve from simple beginnings and a single origin
to the complex and diverse life that characterizes the present earth given the mechanism of
one the most preeminent scientists, Lord
Kelvin, concluded based on some sophisticated calculations that the earth was ~100 million
years old: kelvin was wrong
he thought all changes would be small,
can be caused by copying errors (shuffling, duplication) in the genetic material during
cell division, by exposure to ultraviolet or ionizing radiation, chemical mutagens, or viruses.
New variation also arises duringsexual recombination. Variation is the raw material of
Gene Copy Number
In whippet dogs, a single basepair change makes the
difference between a slender silhouette and the hulking
animal at the right. The mutation inactivates the gene for a
signaling molecule that regulates muscle growth. In animals
with both copies of the gene mutated, muscle growth is
uncontrolled for lack of a “stop” signal.
In pea plants, an 800-base-pair sequence inserted into a gene
produces peas that are wrinkled rather than smooth. The
intruding DNA element disables a gene necessary for starch
synthesis, altering the peas’ sugar and water content. Such
mobile elements are seen in the genomes of most multicellular
organisms, including humans.
Entire genes can be duplicated by copying errors during
cell division, leading to differences between species and
to variation among members of the same species. The
genome of chimpanzees, which eat mostly green plants,
normally contains just a single gene for the starchdigesting
enzyme salivary amylase, whereas humans can
carry up to 10 copies of the gene.
Sequences containing the same base pair repeated eight or
more times are highly prone to copying errors. In pigs, the
gain of two additional C-G pairs in such a sequence
inactivates a gene for a signal receptor in pigment cells,
producing light-colored coats.
most rapid change
Mutations in the DNA that controls when and where genes are
activated can produce profound trait changes by altering the
formation of entire body parts during the organism’s
Changes in the regulatory regions of a single
gene that controls patterns of cell division during stem
development account for much of the shape difference
between the bushy teosinte plant, a type of grass (right),
and its descendant, the tall modern cornstalk ( or maize).
Teosinte and maize are genetically so similar that they
do form hybrids
isolation does evolve, it can take several forms. For example, during courtship females of one
species might refuse to mate with males of another.
genes cannot move from
one species to another if all hybrids between them are dead or sterile.
speciation which occurs when populations get separated geographically
leads to new observations, theories
Physical: Loss of habitat
-Sea level change—Species Area Effect
William Smith (1796)
--different layers of rocks have different fossils
--sequence is invariant from place to place
--fossils can be used as indicators of relative age (position in sequence)
The Map that Changed the World”
GEOLOGIC TIME SCALE
Establishedbefore evolutionary concepts was
• Serves as the empirical observation that
stimulatesthinking about organic change
through time (and evolution)
• No absolute time (years) assigned; only relative
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