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EVOLUTION
By the end of the lesson (s), I can:
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DEFINE the biological process of evolution.
SUMMARIZE the history of scientific ideas
about evolution.
DESCRIBE Darwin’s contributions to scientific
thinking about evolution.
ANALYZE the reasoning in Darwin’s theory of
evolution by natural selection.
RELATE the concepts of adaptation and fitness
to the theory of natural selection.
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The Idea of Evolution
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On Darwin’s travels to the Galapagos Islands he noted
groups of animals.
 Noted that tortoises on the same island resembled
each other closely, while those from neighboring
islands were different
 Noticing similarities and differences among many
animals as he traveled, he became convinced that
organisms had changed over time and he wanted to
know why.
The development of new types of organisms from
preexisting ones over time is called EVOLUTION.
 Modern scientists define evolution as a heritable
change in the characteristics within a population
from one generation to the next.
 Ideas
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of Charles Darwin
In the 18th century most scientists thought that
all species were permanent and unchanging.
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Also they thought that the Earth was only 1000s, not
billions, of years old.
Scientist began presenting evidence that the species
on the Earth have changed over time and more
evidence that the Earth is much older than people
thought.
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In the 1800s European
scientists began studying
the rock layers called
strata.
 They found that strata
were formed as ne
layers of rock are
deposited over time.
 They inferred that in
general lower strata
were formed first and
therefore are older.
 Also found that
different lock layers
hold fossils of different
kinds of organisms.
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Georges Curvier spent years reconstructing the appearance of unique
organisms from fossil records.
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He gave evidence that some organisms in the past differed greatly from any
living species and that some had become extinct.
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Meaning that the species is not living anymore after a certain point in time.
He continued to find many sudden changes in the kinds of organisms he found
in the strata.
He explained his observations as the idea of catastrophism.
The idea that sudden geologic catastrophes caused the extinction of large groups
of organisms at a certain point in time.
 This is no longer accepted by scientist but Cuvier contributed to scientific
acceptance that geologic change and extinction had occurred.
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Charles Lyell shared Cuvier’s ideas but he
thought that the geologic processes that have
changed the Earth’s surface in the past
continued to work the same ways.
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Lyell’s idea is uniformitarianism
Darwin read some of Lyell’s work during travels and
was excited to find how well Lyell’s ideas worked with
his own observations and ideas.
 Lamarck’s
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Ideas on Evolution
Jean Baptiste Lamarck also supported the idea
that populations of organisms changed over
time.
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His idea of inheritance of acquired characteristics,
while not supported states that individuals could
acquire traits during their lifetime as a result of
experience or behavior; then pass on those traits to
their offspring.
 Darwin’s
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Ideas
Descent with modification
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Describes the process of evolution. He carefully
reviewed evidence that points to the notion that every
species, living or extinct, must have descended by
reproduction from preexisting species and that species
must be able to change over time.
Darwin was not the first person to present this idea
but rather was the first to argue that al species had
descended from only one or a few original kinds of life
 Darwin saw the animals of the Galapagos Islands as
evidence of descent with modification.
 He noted that the islands are home to 13 similar
species of finches. Each bird has a beak that has
adapted for a certain kind of food.
 Natural
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Selection
Darwin proposed the theory of natural
selection as the mechanism for descent with
modification.
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Darwin carefully thought about the forces that could
cause changes in organisms over time.
Has for major components:
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Overproduction
 The production of more offspring than can survive to
maturity.
 Each female deer has one or more offspring per year
for many years in a lifetime.
 This increases the population in a short time. But
each new deer needs food and is also vulnerable to
predators and disease. Therefore not all deer live for
very long.
 This thinking was drawn from Thomas Malthus’ work. He
pointed out that human populations can increase more
quickly and that populations are often limited by
conditions such as war, disease, or lack of food.
 Darwin realized that environment limits the population
of all organisms by causing death or by limiting births.
 Genetic
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Variation
Within a population individuals have different traits.
 Some deer have thicker fur or longer legs than
others.
 Variations can be inherited and occasionally new
traits appear in a population.
 Struggle
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to survive
Individuals must compete with each other in
what Darwin Calls struggle for existence.
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Deer that have thick fur may survive I the cold better
than those without thick fur.
A trait that makes individuals successful in its
environment is called an adaptation.
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Differential Reproduction
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Darwin concluded that organisms with the best adaptations are
most likely to survive and reproduce.
Through inheritance those adaptations will become more
frequent in populations.
Darwin used the phrase SURVIVAL OF THE FITTEST to
describe natural selection.
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Fitness in evolutionary terms is the measure of an
individual’s hereditary contribution to the next
generation.
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A FIT individual is one that has offspring that also survive long
enough to reproduce in a given environment.
The term adaptation in evolutionary terms is used to describe
changes in traits in populations over time.
Acclimatization is a short-term process in which physiological
changes take place in a single being in its own lifetime.
 An animal adjusting to a new climate by growing thicker fur.