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Peter Kim
Chapter 22 Descent with Modification w/ explanation of
Transformation Lab
Overview: We all know about Charles Darwin and his
controversial work On the Origin of Species, but many other
scientists before postulated theories about how different species
of animals and plants came into being. Darwin was also
influenced by the works of others such as Jean-Baptiste Lamarck.
Darwin introduced terms such as natural selection,
evolutionary adaptation, and descent with modification.
Evolution - defined as a change over time in the genetic
composition of a population
Remember that it is a population, or in some cases a
species. Individuals never evolve.
This is where biology starts to overlap more with the
humanities rather than the sciences.
Darwin’s “radical” views at the time directly challenged the
church and its beliefs in creation, or that each species had
been made by a god.
This creationist belief was espoused by the first of our
scientists, a guy named Carolus Linnaeus.
He was a Swedish physician and botanist who developed a
system for classifying species, and he founded the branch of
biology known as taxonomy. He also devised the binomial
naming system (Ex. Drosophila melanogaster or the
common fruit fly)
Darwin used the Linnaeus system, but turned it into a tool for
explaining a concept. What was ironic was that Linnaeus
developed this classification system to “glorify god.”
Certain rocks such as limestone or sandstone are known to
be banded, or composed of different “layers”. These layers
are called strata (singular stratum). These are important
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because within these layers are fossils, remains or traces of
organisms from the past.
These fossils are older and older in successively deeper
layers within the rock. Seismic activity or erosion can cause
older layers to be seen and reveal fossils, like dinosaur
bones or arrowheads.
Paleontology, or the study of fossils, was developed by
George Cuvier, a French scientist, who observed in
sedimentary rock that from one stratum to the next, some
species disappear, and other new species appear. He
inferred that extinctions are part of life.
He didn’t agree with the gradual evolutionary view, so he put
forth the idea of catastrophism, that the strata were
separated by catastrophes like floods, droughts, or wildfires.
Another theory at the time was that of gradualism, that
change can take place over continuous but slow changes
that accumulate.
This idea was put forth by Scottish geologist James Hutton.
A key idea here is that his theory could be explained by
current gradual mechanisms.
Charles Lyell, the leading geologist in the era when Darwin
was around, took gradualism and put it in a broader theory,
that of uniformitarianism. Lyell that those same gradual
changes that happened in the past happened at the same
rate as the processes today.
One of the few people who put forth an idea of how life
evolves, French biologist Jean- Baptiste Lamarck had two
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The first, on use and disuse, stated that anything that was
not essential to the organism’s survival (e.g. was not used), it
would be lost in the organism’s evolution.
The second, inheritance of acquired characteristics,
stated that any modifications that occurred over an
organism’s lifetime could be inherited by its offspring.
Lamarck also thought that organism’s had an innate drive to
become more complex.
Darwin disagreed in favoring his idea of natural selection,
but he also believed in the misconception of inheritance of
acquired characteristics. Remember, acquired
characteristics can NOT be passed on. Think about it, if that
was true, and you somehow learned to walk the entire time
on your hands, your offspring would also walk on their hands
from birth.
We begin with Charles Darwin, here’s the laydown.
Born in Shrewsbury, England
Always fascinated with nature as a boy
His father sent him to the University of Edinburgh to study
Darwin could not stand to see surgery being done and was
always nauseous, especially since there was no general
anesthesia back then
So he decided to attend Cambridge University to become a
While studying under Reverend John Henslow, a botany
professor, he recieved his B.A.
Henslow recommended Darwin to Robert FitzRoy, who was
preparing a journey around the world on the HMS Beagle
Darwin spent much time collecting animal samples and
studying the various flora and fauna of South America,
because the ship’s job was to plot the coastline
An important observation he made was that animals and
plants in certain climates in South America more closely
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resembled other animals in different climates in South
America than areas with the same climate in places like
While on board the ship, Darwin read Charles Lyell’s
Principles of Geology, of which he found examples and
samples that reinforced those views
Finally the most influential stop Darwin made was at the
Galapagos Islands
The observations he made about the animals there being
found nowhere else served as an example for his theory
While on this trip, Darwin corresponded with many other
scientists such as Lyell and Henslow
By 1844, Darwin finished writing his essay on the origin of
species and natural selection. However he did not want to
publish it, since he knew it would cause an uproar
Lyell, however, urged him to publish it before someone else
came to the same conclusions
This came true. In June 1858, Darwin received a manuscript
from a British naturalist named Alfred Russel Wallace
Darwin then sent the manuscript to Lyell, who presented it to
the Linnean society, and finished his paper and published it
a year later
Wallace, however, was in such awe of Darwin that he agreed
that Darwin was the main architect of the theory of natural
Darwin called his view of life descent with modification, a
term he used instead of evolution
These are the main point:
Observation: Population growth is exponential if unchecked
Observation: Populations however remain stable
Observation: Resources are limited
Observation: Members of a population vary, no two
individuals are alike (except twins)
Observation: Much of this variation is heritable
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Inference: Production of more individuals leads to
competition for various resources, such as food and mates
Inference: Survival depends on inherited traits. Those who
inherit traits that allow them to better compete for resources
leave more offspring
Inference: This unequal ability leads to a gradual change in
the genetic composition of a population
Artificial selection - Taking plants or animals with desired
traits and breeding them to create the desired individuals
Example is wild mustard, when humans picked larger
flowers and stems, larger flower clusters, larger terminal
buds, larger lateral buds, larger leaves, or larger stems, they
got from the mustard, broccoli, cauliflower, cabbage, brussel
sprouts, kale, and kohlrabi respectively. This shows that
humans can induce natural selection artificially to create new
species for use.
Another example is maize, or corn. In genetic terms this is a
complete failure, as the cob is completely surrounded by the
sheath and would rot if not harvested by humans. In other
words, it completely depends upon humans.
Natural selection is the differential success in reproduction
among individuals that vary in their heritable traits. These
reproductive differences emerge as each individual interacts
with its environment
Over time, natural selection can increase the adaptation of
organisms to their environment
If an environment changes over time, or if individuals of a
particular species move to a new environment, natural
selection may result in adaptation to these new conditions,
or maybe it could give rise to new species
Homology is the fact that all organisms have similar bones
in the body, etc., an explanation for how we are all
descended from the same ancestor
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Vestigial organs are remnants of our previous evolution,
such as out tailbone, a reminder that our ancestor had tails
The final key terms are biogeography and endemic
Biogeography describes the fact that certain similar species
exist in similar ranges climates, and parts of the world
Endemic refers to where a certain species is localized to.