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Chapter
10
Principles of
Evolution
Section 10.1: Early Ideas About Evolution
• Evolution- the process of change over time by
which descendents come to differ from their
ancestors.
• The man given credit for the findings on
evolution is Charles Darwin; however, he
wasn’t the first to talk about it.
• The concept had been discussed for more
than 100 years.
Section 10.1: Early Ideas About Evolution
• Carolus Linnaeus- Developed a
classification system for all types
of organisms in the 1700’s.
• He believed organisms changed
through hybridization which was
crossing of genes.
• He believed this produced new
species.
• Species are groups of organisms
that can reproduce and have
fertile offspring.
Section 10.1: Early Ideas About Evolution
• Georges Leclerc De Buffonproposed that species shared
ancestors instead of rising
separately.
• He also argued the earth was
more than 6000 years old.
Section 10.1: Early Ideas About Evolution
• Erasmus Darwin- Grandfather of
Charles Darwin.
• He concluded that more complex
life forms came from lesscomplex forms.
Section 10.1: Early Ideas About Evolution
• Jean-Baptiste Lamarck- Early
1800’s proposed that all
organisms evolved towards
perfection and complexity.
• He also believed that if you
stopped using part of your body,
you would lose it over time and
that characteristic could be
passed on.
Section 10.1: Early Ideas About Evolution
• For Darwin’s theory, the age of the Earth was the
key issue.
• They belief of that time was the Earth was about
6000 years old.
• Early scientists who studied fossils believed it
was much older.
Section 10.1: Early Ideas About Evolution
• Scientists who believed that Earth was relatively
young believed in catastrophism, which states
that natural disasters create very quick and
sudden changes.
• Scientists who believed the Earth was old
believed in gradualism, which argued that things
change over long periods of time slowly.
• Geologists James Hutton studied the Earth and
decided things like “The Grand Canyon” couldn’t
have formed that quickly.
Section 10.1: Early Ideas About Evolution
• One of the leading proponents
of Earth being old was
economist Charles Lyell.
• Lyell took Hutton’s gradualism
concept and expanded it to
unifomitarianism.
• This belief stated that processes
that shape the Earth are
uniform throughout time.
• Lyell and Hutton gave Darwin
the information he needed to
prove evolution as a theory.
Section 10.2: Darwin’s Observations
• As Darwin traveled and
observed, he was shocked
by the number of
different traits among
similar species.
• When Darwin visited the
Galapagos Islands off the
coast of South America,
he noticed much variation
among species.
• He also noticed these
variations suited the
environment these
animals were living in.
Section 10.2: Darwin’s Observations
• For example:
– Certain tortoises that have long necks and legs live on
islands with tall plants.
– Tortoises with short legs and necks lived on islands
that grew low vegetation and lots of ground moss.
Section 10.2: Darwin’s Observations
• Another example was finches.
• Finches with strong, thick beaks lived in areas
that had large hard-shelled nuts and those
finches with short delicate beaks lived on islands
rich in insects and fruits.
Section 10.2: Darwin’s Observations
• Was this just a coincidence or was there
something happening to the species?
• Darwin determined that organisms must
somehow be able to adapt to their environment.
• An adaptation is something that allows an
organism to better survive in its’ environment.
Section 10.2: Darwin’s Observations
• On his voyages, Darwin found fossil evidence of
organism’s changes.
• He found fossils similar to living organisms today
and also found sea-life fossils on tops of
mountains.
– This meant that at one time the mountain was under
water and it had to take a long time for the water to
fall and mountain to rise.
– To Darwin, this proved that the Earth was old!
Section 10.3: Theory of Natural Selection
• Darwin came back after his voyages and spent 20
years researching about his findings.
• He was especially influenced by his homeland of
England.
• He was very intrigued by farmers and breeders.
• Darwin noticed that a lot of domesticated plants
and animals showed many different traits that
were not shown in the wild.
• What was happening was farmers were selecting
which organisms would reproduce so the best
traits would be passed on.
Section 10.3: Theory of Natural Selection
• When humans select which organisms breed,
this is called artificial selection.
– Farmers only let big cows mate with big cows
because they are paid by the pound.
Section 10.3: Theory of Natural Selection
• Darwin concluded that something like this must
occur in nature.
• Obviously, humans have nothing to do with
wildlife interbreeding; however, Darwin believed
that some type of selection occurred.
• Darwin termed this natural selection.
Section 10.3: Theory of Natural Selection
• Natural selection is a mechanism by which
individuals that have inherited beneficial
characteristics produce more offspring than
other organisms do.
• In natural selection, the environment is the
selective agent.
Section 10.3: Theory of Natural Selection
• Another important piece of information that
Darwin used came from an English Economist
Thomas Malthus.
• Malthus had proposed that resources such as
food, water, and shelter were natural limits on
population growth.
• Darwin took this information and reasoned that
this affected species in nature.
– He called this the “struggle for survival”
Section 10.3: Theory of Natural Selection
• If resources are limited and organisms have more
offspring than can survive, Darwin wanted to
know which ones survived and why?
• Darwin summarized that the answer was in the
variation within a population.
• A population is a group of individuals that lived
in the same area.
Section 10.3: Theory of Natural Selection
• Darwin figured out that variation in
traits were well suited for their
particular environment.
• He called this “Descent with
Modification”.
• Darwin finally put all his findings
together.
• He published a book called “On The
Origin of Species By Means Of
Natural Selection”.
Section 10.3: Theory of Natural Selection
• In Darwin’s book there are 4 main principles:
1) Variation:
– The differences that exist in every population are
the basis for natural selection.
– Differences that are best suited for their
environment get passed on to offspring.
Section 10.3: Theory of Natural Selection
• In Darwin’s book there are 4 main principles:
2) Overproduction:
– More offspring are produced that can possibly
survive.
– This creates competition between offspring for
resources.
Section 10.3: Theory of Natural Selection
• In Darwin’s book there are 4 main principles:
3) Adaptation:
– Most times variation allows individuals to survive
better in the environment that they live.
– More successful individuals are “naturally selected”
to live longer and produce more offspring.
Section 10.3: Theory of Natural Selection
• In Darwin’s book there are 4 main principles:
4) Descent with Modification:
– Over time, natural selection will result in species
with adaptations that suit their environment.
•
Jaguars:
–
Teeth and jaw size
Section 10.3: Theory of Natural Selection
• Adaptation leads to fitness.
• Fitness is the measure of the ability to survive
and produce more offspring relative to other
organisms.
• The fitness only remains if the environment
remains constant.
• As the environment changes, the traits that were
once more favorable, may become less favorable
and new adaptations will be needed.
Section 10.4: Evidence of Evolution
• Darwin found many sources of evidence for
evolution:
1) Fossils- fossils found in older layers of rock
differed from fossils in younger layers of rock.
2) Geography- similar organisms were found on
different mainlands.
3) Embryology- looking for similar development in
the womb.
4) Anatomy- Some of Darwin’s best evidence came
from comparing body parts of different species.
Section 10.4: Evidence of Evolution
• Anatomy (continued)
– Homologous structures are features that are similar
in structure but have different functions in different
organisms.
– For example, the human hand, mole feet, and a bat’s
wing all have very similar structures, but different
functions.
– To Darwin, this proved common ancestory.
Section 10.4: Evidence of Evolution
• However, organisms can have structures that are
used for similar purposes but are not anything
alike structurally.
• This is called analogous structures
– Example: a fly’s wing and a bat’s wing
Section 10.4: Evidence of Evolution
• Some organisms still show signs of structures
that are no longer used for their original purpose
or lack any usefulness at all.
• These are called vestigial organs.
• Vestigial structures are remnants of organs or
structures that had a function in early ancestors.
Section 10.5: Evolution Today
• Fossils provide a record of evolution.
• The study of fossils or extinct organisms is called
paleontology.
• Fossil evidence is not complete because most
organisms die and decay; however, no scientist
has ever found a fossil that contradicts evolution.
• Paleontology was a new science in Darwin’s time.
• Darwin worried about gaps in the fossil record;
however, since his time many of those gaps have
been filled.
Section 10.5: Evolution Today
• Scientist use DNA sequence analysis and protein
comparisons to link past fossils to today’s
organisms.
• Scientist still today actively try to find more
pieces of the puzzle relating to evolution.