Download Ideas That Shaped Darwin*s Thinking

Ideas That Shaped Darwin’s
Thinking
Ch 15-2
Darwin’s voyage came during one of the most
exciting periods in the history of Western science.
If he’d lived in an earlier time, Darwin might have done nothing more than
think about the questions raised during his travels… but in Darwin’s day, great
thinkers were beginning to challenge the established and traditional views
about the natural world.
Darwin was powerfully influenced by the work of these scientists, especially
those studying the history of the Earth. In turn, his work greatly changed the
thinking of many scientists and non-scientists alike.
Some people, however, found Darwin’s ideas too
shocking to accept.
To understand how radical Darwin’s thoughts
appeared, you must understand a few things
about the world in which he lived.
Most European people believed that Earth
and all its life forms had been created by God
only a few thousand years ago.
Since that creation, they concluded, neither
the planet nor its life forms had changed.
Rocks and major geological features were
thought to result from sudden catastrophic
events that humans rarely, if ever, witnessed.
By the time Darwin set sail, numerous new discoveries had
resulted in a rich fossil record that was challenging the
traditional view of life.
Some scientists were adjusting their beliefs to
include not one, but several periods of creation.
Each of these periods, they reasoned, was preceded
by a catastrophic event that killed off many forms of
life.
Darwin began to realize that what he had observed
did not fit neatly into this view of unchanging life.
Slowly, and after studying many scientific theories of
the time, Darwin began to change his thinking
dramatically.
James Hutton’s Ancient, Changing Earth
During the 18th and 19th centuries, scientists examined Earth in great detail and gathered
information suggesting that it was very old and had changed slowly over time.
In 1795, geologist James Hutton, published a detailed hypothesis about the geological forces that
have shaped earth.
Hutton proposed that layers of rock form very slowly. He added that some rocks are moved up by
forces beneath Earth’s surface, others are buried, and still others are pushed up from the seafloor to
form mountain ranges. All these rocks, mountains, and valleys are then shaped by a variety of
natural forces, including rain, wind, heat, and cold temperatures.
Most of these geological processes take millions of years to occur, therefore, Hutton proposed that
Earth had to be much older than just a few thousand years as believed.
Charles Lyell stressed that scientists must explain past events in
terms of processes that they can actually observe, since processes
that shaped the Earth millions of years earlier continue in the
present.
Just before setting sail on the Beagle, Darwin was given a copy of Lyell’s Principles of Geology.
Lyell’s work explained how geological features could be built up or torn down over long periods of
time. This understanding helped Darwin appreciate the significance of the geological phenomena
he witnessed -- including a volcanic eruption and an earthquake.
His understanding of Lyell’s geological teachings influenced Darwin in two important ways:
1. First, Darwin asked: If the Earth can change over time, can organisms change as well?
2. Second, he realized that it would have taken many, many years for life to change in the way
he was suggesting… this would be possible only if the Earth were extremely old.
Hutton and Lyell used geological features such as these
huge sandstone rocks as evidence to show that Earth was
many millions of years old rather than just a few thousand.
Jean-Baptiste Lamarck, a French naturalist, was one of the
first scientists to propose that living things have changed
over time and that all living species were descended from
other species. He also realized that organisms were
somehow adapted to their environments.
He published his hypothesis in 1809, the year Darwin was
born. Unfortunately, his hypothesis was incorrect in
many ways, but he was one of the first to develop a
scientific theory of evolution and also to realize that
organisms are adapted to their environments, paving the
way for the work of later biologists.
Lamarck proposed that by selective use or disuse of organs, organisms
acquired or lost certain traits during their lifetime. These traits could
then be passed onto their offspring. Over time, this process could lead
to change in a species.
Lamarck’s Evolution Hypotheses
1. Organisms are naturally inclined
towards complexity and perfection, so if
you want to fly… keep flapping your arms
and eventually you’ll be able to! NOPE!
2. Selective use or disuse of an organ
leads to a change in that organ that can
be passed onto offspring, if you want to
lose your wings, just stop flying and they’ll
go away! NOPE!
3. Acquired characteristics can be
inherited, so if you go to the gym and work
on that six-pack… your children will have
six-pack abs, too! NOPE!
Thomas Malthus, Population Growth, and Darwin
Another important influence on Darwin
came from a book published in 1798 by
the English economist Thomas Malthus.
Malthus noted that babies were being
born faster than people were dying and
reasoned that if the human population
continued to grow unchecked, sooner or
later there would be insufficient living
space and food for everyone.
Malthus observed that the only forces
working against human population growth
were war, famine, and disease.
Darwin realized that Malthus’s reasoning
applied even more strongly to plants and
animals than it did to humans.
Why? Because humans reproduce at a much
slower rate than most other species do. In one
summer, a single tree can produce thousands of
seeds while one oyster can produce millions of
eggs. If all those offspring survived, the world
would be overrun in just a few generations!
This does not happen because the overwhelming
majority of a species’ offspring die. Further, only a
few of those offspring that survive actually succeed
in reproducing.
What causes the death of so many individuals?
What factor(s) determine which ones survive and
reproduce and which do not? The answers to
these questions became central to Darwin’s
explanation of evolutionary change.
Origins of Evolutionary Thought: A Summary
The groundwork for the modern theory of evolution was laid
during the 1700s and 1800s. Charles Darwin developed the
central idea of evolution by natural selection, but others before
1785, James Hutton proposes that Earth is shaped by
1831, Charles Darwin sets sail on the H.M.S. Beagle, a
and
during
hisover
time
also
parts of the theory.
geological
forces
that took place
extremely
long built essential
voyage that will provide him with vast amounts of
periods of time. He estimates Earth to be millions (not
thousands) of years old.
1798, Thomas Malthus predicts, in his Essay on the
Principle of Population, that the human population will
grow faster than the space and food supplies needed to
sustain it.
1809, Jean-Baptiste Lamarck publishes his hypotheses
of the inheritance of acquired traits. The ideas are
flawed, but he is one of the first to propose a
mechanism explaining how organisms change over time.
evidence leading to his theory of evolution.
1833, Charles Lyell publishes his second and final
volume of Principles of Geology, explaining that processes
occurring now have shaped Earth’s geological features
over long periods of time.
1858, Alfred Wallace writes to Darwin, speculating on
evolution by natural selection, basd on his studies of the
distribution of plants and animals.
1859, Charles Darwin publishes On the Origin of Species
Find the Google Doc you created at the end of section 15-1
1. Create a new heading and label it, “ 15-2: Ideas That Shaped Darwin’s
Thinking”
2. Answer the 5 Section Assessment questions found on p. 377 of your
text. You must type the questions and the answers