Chapter 22 Presentation-Descent with Modification

Evolutionary history is an especially
challenging area of science because
experiments cannot be performed to
establish past events or their causes.
There are nonetheless scientific methods
of establishing beyond reasonable doubt
what happened in some cases. How do
these methods compare to those used by
historians to reconstruct the past?
Chapter 22 Evidence for
“All truths are easy to understand once
they are discovered; the point is to
discover them.”--Galileo
Essential Idea
There is overwhelming evidence for the
evolution of life on Earth.
Charles Darwin
The man responsible for brining the
idea of evolution and natural selection
to the forefront of science.
His book, The Origin of Species,
presented his idea of descent with
Although parts were wrong, or erroneous,
the majority of it is correct. The errors
were due mostly to the limitations of
science at the time.
Prior to Darwin
Prior to Darwin, there were a number
of explanations that sought to explain
life, how it arose, and it did/did not
Development of the Theory
There were many scientists who
studied the history of the earth and the
life that inhabits our planet.
Georges Cuvier (1769-1832)
Developed the science of paleontology while
he studied layers of rock around Paris
He noted that the deeper layers of rock
contained fossils that were more dissimilar
than current life.
From one stratum to the next, many
characteristics disappeared and others
formed. Thus, he concluded, extinctions
must have been common throughout the
history of life.
Georges Cuvier
Cuvier was staunchly opposed to the
idea of gradualism.
Rather, he advocated catastrophism-the idea that a local catastrophe such
as a flood or drought was responsible
for the changes observed in species-their extinction. As these organisms
were wiped out, new species
repopulated the region.
James Hutton (1726-1797)
In contrast to catastrophism, Hutton
proposed the idea of gradualism--slow,
cumulative, continuous change results
in profound change.
His examination of the geological
features of Earth allowed him to
propose parallels between the Earth’s
history and life (1740’s-50’s).
Charles Lyell (1797-1875)
Lyell, a great geologist, incorporated
Hutton’s ideas into a theory called
uniformitarianism--which states that the
same processes of the past are taking
place today at the same rate.
Hutton was a horrible writer.
Lyell wrote The Principles of Geology
The Effect on Darwin
Lyell and Hutton had a great impact on
Darwin. Darwin felt that if these two
were right, then the Earth is much
older than 6,000 years as theologians
Also, he presumed, if these process
could act on the Earth, then they could
also act on living organisms producing
slow and gradual change.
Jean Baptist de Lamarck
Lamarck is often remembered for his
erroneous interpretation for how
evolution occurs--inheritance of
acquired characteristics.
However, he has made many useful
contributions to science.
For example, he was the first scientist to
propose the idea that evolutionary change
can explain the fossil record (early 1800’s).
In 1861, Darwin said of
“Lamarck was the first man whose
conclusions on the subject excited much
attention. This justly celebrated
naturalist first published his views in
1801. . . he first did the eminent service
of arousing attention to the probability of
all changes in the organic, as well as in
the inorganic world, being the result of
law, and not of miraculous interposition.”
In 1801, Lamarck Wrote...
“. . . time and favorable conditions are
the two principal means which nature
has employed in giving existence to all
her productions. We know that for her
time has no limit, and that consequently
she always has it at her disposal.”
Jean Baptist de Lamarck
Lamarck compared current species with
fossil forms and chronicled an older to
younger line of descent from fossil to
living species.
His 2 principles:
Use and disuse-as determined by the
Inheritance of acquired characteristics.
Jean Baptist de Lamarck
Lamarck also held the belief that an
innate drive to be more complex was
responsible for the observed change in
Jean Baptist de Lamarck
Lamarckian inheritance, based upon
the notion of use and disuse, was a
perfectly reasonable hypothesis at the
Many of his contemporaries, including
Charles Darwin, subscribed to the
principle of use and disuse.
Jean Baptist de Lamarck
With the rediscovery of Mendel’s work
in the early 1900‘s which largely
explained the mechanism of inheritance,
Lamarck’s ideas were largely rejected
by science in favor of Darwin’s theory
of natural selection.
To be clear, you should understand
that characteristics acquired during
one’s lifetime are not heritable.
Darwin’s 2 Key Points
1. He presented evidence that many species
of organisms on Earth are descendants of
ancestral species which were different from
modern species. These descendants are
chronicled in the fossil record.
2. He proposed a mechanism for this
change--natural selection. The crux of
natural selection is that populations will
change over time as individuals become more
fit for their environment.
Our Current Understanding
Our current definition of evolution is
referred to as a change over time in the
genetic composition (heritable
characteristics) of a population.
Eventually, enough change will
accumulate in a population that it will
constitute a new species.
The Uproar
What made the idea of Darwinism so
abrasive at the time is that it
challenged traditional beliefs of
Western culture:
1. The Earth is only a few thousand years
2. All species which now exist have been
here since the beginning.
Darwinism challenges worldview.
Darwin’s Ride on the HMS Beagle
Darwin was deeply impressed by the
work of Charles Lyell. His belief in
Lyell’s principle of uniformitarianism
was solidified when he witnessed a
huge earthquake while in S. America.
This firsthand observation of the
Chilean coastline rising several feet as a
result of the quake got him thinking.
Darwin’s Ride on the HMS Beagle
Further exploration and his finding of
marine fossils high up in the Andes
mountains enabled him to understand
how similar earthquakes over a long
period of time could result in such
He was now realizing that the physical
evidence wasn’t supporting traditional
Darwin’s Ride on the HMS Beagle
These ideas really sparked Darwin’s
interest and when he arrived at the
Galapagos he was intrigued by what he
saw. Many of the species of animals he
observed existed no where else in the
He did not notice the significance of
any of these observations until he
returned home to England.
Back Home in England
Darwin started to notice changes as he
examined his specimens after the trip.
For instance, he noticed that many of
the birds of the Galapagos resembled
birds from the mainland of S. America.
His hypothesis was that somehow a bird
from the mainland must have colonized
the Galapagos, and through gradual
change diversified into the many forms
now seen on the island.
Back Home in England
Darwin also began outlining the major
features of the theory of natural
He was reluctant to publish these
because of the outrage he knew they
would cause.
Lyell urged him to publish because he
was afraid someone else working on
the same thing would beat him to it.
Alfred Russel Wallace (1823-1913)
 A young British naturalist named Alfred Russel
Wallace did beat him to it (~1858).
 While studying in the East Indies (1854-1862),
Wallace sent a paper to Darwin for review and the
paper basically said the same thing as Darwin’s did.
 Fortunately for Darwin, Wallace greatly admired him
and gave him full credit for the development of the
theory of natural selection.
Charles Darwin
Unlike his predecessors, Darwin was able
to convince the biological community his
theory is correct because of his reasoning,
logic, and the overwhelming amount of
supporting evidence.
Darwin’s publication presented 2 main
1. Evolution explains the unity and diversity
of life.
2. Natural selection is the cause of adaptive
Natural Selection
The main ideas of natural selection are:
1. Natural selection is the differential
reproductive success of individuals and their
2. Over time, natural selection increases the
adaptations of organisms to their
3. If an environment changes over time, or
an individual moves, natural selection may
result in adaptations to new conditions and
Main Points of Natural Selection
1. Natural selection occurs through individuals and
their environment.
2. Individuals don’t evolve.
3. A population is the smallest unit that can
4. Evolution is measured only as changes in the
relative proportions of heritable variation in a
population over multiple generations.
5. Natural selection only amplifies inheritable
traits, not acquired characteristics.
6. Natural selection is always operating, but which
traits are favored depends on the environment.
Domesticated Animals
Using your device, find explain 2
examples of the evolution of
domesticated animals.
Rock Pocket Mouse Example
Here is another example that illustrates
how the success and traits of
individuals vary with the environment in
which they live.
Key Points Arising from Such
1. Natural selection is an editing process
rather than a creative mechanism.
2. Natural selection depends on time and
place. It favors characteristics in a
genetically variable population that
increases the fitness in the current
Homologies and the tree of life are
important in explaining ancestry.
Homologies shared by a greater
number of species are likely to have
evolved earlier on in history and are
further down on the tree of life.
Homologies that have evolved more
recently are seen on only small
branches of the tree.
Example: tetrapods--the vertebrate
branch consisting of birds, amphibians,
mammals and reptiles.
They all have the same 5-digit limb structure
which indicates these mammals all share a
common ancestor.
Similarities which result from common
ancestry are known as homologies.
Forelimbs of all mammals show the same
arrangement of bones from shoulder to
finger tip.
These occur even if the structure is used for
a completely different function.
These anatomical differences would not have
arisen in a new species if they didn’t share a
common ancestor.
Such structures are said to be
homologous structures--which are
variations on a common theme that
was present in the common ancestor.
Molecular homologies exist as well--the
genetic machinery of DNA and RNA also
points to a common ancestor; the
existence of Hox genes in development.