One today. In Lyell’s book, he explains

One of the predecessors of Charles
Darwin that impacted his work was Charles Lyell. Lyell was a geologist who had
the belief that the world was older than we thought, millions of years old to
be in fact. He also wrote the book that Darwin took with him on his trip on the
Beagle, Principles of Geology. This
helped Darwin fill in the missing gaps that he had when building a timeline for
his theory of evolution. Not only was he a geologist, but more specifically he
studied stratigraphy due to his interest in the layers of the earth and geological
changes such as earthquakes. He did, in fact, explain why earthquakes happen
with his theory of volcanic pressure building underneath the earth’s surface.
He was also responsible for the nomenclature of the time periods, or eras such
as the Mesozoic, that we still use today. In Lyell’s book, he explains that he
believes that the word does not change vastly and immediately, but continuously
and gradually over time, and still does today. This goes hand in hand with
Darwin’s theory but greatly differs from the theory of Darwin’s other
predecessor, Georges Cuvier. Lyell was not completely against Cuvier, he did
actually somewhat agree with his idea that species did not change, and that
they remained specific and permanent. He believed that some species did go
extinct due to a battle of survival, but not in the catastrophic events that
were referred to be Cuvier. Interestingly enough, even though Darwin and Lyell
did not completely agree on certain aspect they still remained good friends.

Another
predecessor of Charles Darwin was Georges Cuvier. Cuvier was a French scientist
who totally dismissed Jean Lamarck’s theory of evolution. He believed that
species were made perfect by God and they did not change over time. Georges
studied anatomy, and with his familiarity with bones and fossils, he deemed
evolution impossible due to the fact that the fossils that were found are still
the same as living species’ bones today. Cuvier also was the first to introduce
the term extinction. Before he
introduced the idea of extinction, most people of his time thought that these
“extinct” species were just unable to be found, or in a sense “hiding”. Georges
disproved this by comparing the fossils of mammoths with those of elephants. He
deemed that an animal the size of a mammoth could not just be hiding somewhere,
but would rather have died off during a mass catastrophic event. His theory
went along with the stories of the Bible,
of the huge flood that wiped out a mass number of species. Charles Darwin,
on the other hand, thought that species gradually changed and those that did
not have the means to survive died off, while the stronger species, more adapted
to their environment, survived.

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One of Darwin’s
major observations that support his theory of evolution is the unity and
diversity of life. Unity simply stating that all species share a common
relative or ancestor, and diversity stating that each species adapted to their
environments differently or in his primary definition of evolution, descent
with modification. Examples of this would be with the Galápagos tortoises. The
tortoises began to spilt off into different parts of the island, some went where
the food source was higher in the branches while others went where the food
source was down low. With this, the tortoises started to adapt differently to
their own environment. The ones that went where food was higher in branches,
began to have a higher curvature in their shell so that they could stretch
their necks upward. While the tortoises that went where the food source was
low, their shells began to curve down so that it was easier for them to bend
their necks down so that they could get their food. Obviously this didn’t
suddenly happen, but over time with “descent with modification”.

The second of Darwin’s major
observations is natural selection. In his view of natural selection he came up
with three observations and then three inferences explaining those
observations. In these observations he mentioned that most species produce more
or have the ability to produce more offspring than the earth can sustain.
However, most offspring don’t survive long enough to reproduce, or become
unable to reproduce all together. This is what keeps the population at bay to
maintain balance. His last observation is that the earth doesn’t have enough
resources to keep every possible species and all of their offspring alive. This
being said, that means that there is a “fight” for survival. Mother nature is
rough, and some offspring are not built to maintain life. Those offspring that
do survive end up reproducing and passing on the traits that kept them alive,
and further down the line those traits get strengthened and more dominant. An
example of this could be with chameleons. The iguana is the closest living
relative to the chameleon, but as you can see they are quite different. The
chameleon can change its, rotate its eyes 360 degrees, and shoot its tongue to
catch prey at extreme speeds. These traits must have been favorable in its
environment and passed down along the generations to make the chameleon what it
is today.