Chapter 16: Evolutionary Theory
I. Developing a Theory
A. A Theory to Explain Change Over Time
1. Evolution is process of change by which new species develop
from existing species over time.
2. A theory is a hypothesis that has been consistently proven by
experimentation & observation.
3. Who is the “father” of evolution? Charles Darwin 1809 – 1882
B. Darwin’s Ideas from Experience
1. How did Darwin gather his information which enabled him to
develop his theory of natural selection? While on his voyage he
made observations about different plants & animals. Also
collected plants & animals from different areas in South America
2. What did Darwin notice about the armadillo fossils as compared
to the living armadillos in South America? They were alike in
certain ways, but they were also different.
3. Where did Darwin propose the plants & animals on the Galapagos
Islands (604 miles away from S. America) came from? What
evidence did he have for his idea? From South America; many of
the plants & animals on the islands were similar but not identical
to the plants & animals he saw in S. America.
4. There are 13 or 14 different species of finches on the Galapagos
Islands; how did they get there & why were they different from
one another? A small group had migrated in some way from S.
America. They all have different types of beaks, depending on
the foods they eat; heavy beaks for crushing seeds, thin beaks
for eating insects, etc. Over time they evolved into the
13 – 14.
5. Descent with modification means that offspring/descendants of
organisms are slightly different/modified from their parents.
C. Years of Reflection
1. Darwin’s voyage on the HMS Beagle began in 1831 & ended in
1836; he was 27 years old when he returned to England.
2. Why didn’t he report his observations & propose his theory of
evolution right away? Afraid of what the Church might say &
wanted to be sure of his observations. The Church said that all
things on Earth had not changed since the creation.
D. Breeding & Selection
1. What did Darwin learn by breeding pigeons?
Learned that breeders pick & choose traits that they like in the
plants or animals they breed.
2. What is artificial selection?
The breeder picks & chooses the mates for the organism.
3. How do we use artificial selection?
Used to breed dogs, cats, horses, food crops, etc.
E. Darwin’s Ideas from Others
1. How did most people from Darwin’s time believe species came to
be? Created all at once by God; they were created once &
remained the same forever.
2. Lamarck was a French scientist. In 1809 he proposed that
organisms change due to use & disuse of a character & this would
be passed on to their offspring. Give an example of this.
Giraffes got their long necks by stretching their necks while
reaching for food. This “trait” was then passed on to offspring.
Is this true? NO
3. What belief did Darwin & Lamarck share?
Organisms change over time as they adapt to their environment.
4. In 1798, what did the English economist Thomas Malthus observe
about the human population & the food supply? Human
population was increasing faster than the food supply.
5. According to Malthus, what factors would keep the human
population from increasing the way it was? Disease, war &
famine (lack of food) would cause many humans to die.
6. What did Darwin notice about ALL populations of organisms?
They all tend to produce more offspring than can survive.
7. What does the science of geology study? The study of the
formation of the Earth & rocks.
8. What did the geologist Cuvier notice about fossils? That they
were similar to organisms that were living at that time, but they
were also different.
9. What did the geologists Hutton & Lyell think about geological
processes? Thought that the geology of the Earth is constantly
changing based on their observations.
10.What did Darwin learn by reading Lyell’s book? Both of their
ideas & observations about the Earth & how organisms change
over time were very similar.
II. Section 2: Applying Darwin’s Ideas
A. Evolution by Natural Selection
1. Natural selection is the process by which organisms that are
better adapted to their environment survive, reproduce & pass
these traits on to their offspring.
2. What process did Darwin believe causes evolution?
Natural selection Per 7
3. What does Darwin’s Theory of Evolution by Natural Selection
predict? Over time the number of organisms that carry
advantageous traits will increase in a population. Why? Natural
selection; those best adapted survive & reproduce putting those
genes into the gene pool.
4. Discuss Darwin’s Theory of Evolution by Natural Selection
a. Overproduction – every population of organism is capable of
producing more offspring than the environment can support.
b. Variation – there’s variation within all organisms in the form
of their inherited traits. Variation exists within every
population.
c. Selection - certain members of a given population have a
better chance of surviving than others; therefore, some
individuals of the species leave more offspring than others.
d. Adaptation – over time, those traits that improve an
organism’s chances of surviving & reproducing become more
common in the gene pool.
5. Does the insect pictured in Figure 5 on page 380 fit in with
Darwin’s Theory of Evolution by Natural Selection? Support your
answer. Yes, the insect looks like a leaf & so it is better
camouflaged from predators. This increases its chances for
survival & reproduction. The trait gets passed on to its offspring
& this increases their chances of survival.
6. Adaptation is a trait that improves an organism’s ability to
survive & reproduce. Ex: An insect that resembles a leaf.
7. Populations & species evolve, NOT individuals. What is a species?
It is a group of organisms that is closely related, can interbreed
& produce FERTILE offspring.
8. When did Darwin finally write an outline of his ideas about
evolution & natural selection? 1844 – 8 years after returning
from his voyage.
9. What finally motivated Darwin to publish his book On the Origin
of Species by Natural Selection in 1859? Darwin realized that the
naturalist named Wallace had the same theory that he did about
evolution.
B. What Darwin Explained
1. Darwin used information from natural history, economics, geology
& the fossil record to develop his theory of evolution by natural
selection. Today we use other areas of science to explain the
process of evolution by natural selection.
2. Evidence of Natural Selection & Evolution
a. Fossils – traces of organisms that lived in the past. May be
preserved in sedimentary rocks, encased in tree sap that turned
into amber, or bones that have been replaced by minerals.
 What evidence do we have to support Darwin’s idea that
whales descended from 4-legged, land-dwelling animals?
Discovered a series of 4 skeletons that support his
hypothesis (see p. 382).
b. Biogeography – the study of the locations of organisms
around the world.
 Explain how similar organisms, like the rhea, ostrich, &
emu are found on 3 different continents. They evolved
on 3 different continents with similar habitats; the
similar habitats shaped their evolution in similar ways.
This is known as convergent evolution.
 Is this an example of natural selection? Explain your
answer. Yes, the environment “selected” for certain
traits.
c. Developmental Biology/Embryology
 What do you notice about all of the embryos in row 1?
They’re very similar.
 Can you tell which embryos will develop into the fish &
salamander in row 2? Yes, the first & second embryos
with their long tails.
 What does the similarity between all of the embryos in
row 1 tell you about these organisms? They all evolved
from a common ancestor millions of years ago.
d. Anatomy
 What are homologous structures?
Characteristics similar in 2 or more species that have
been inherited from a common ancestor of those
species.
 Give an example of a homologous structure in the
human, alligator, bat, & penguin. The front legs/limbs;
similar in structure but different in function.
*Forelimb of alligator for walking
*Arm of human for carrying, throwing, grasping
*Wing of bat for flying
*Flipper of penguin for swimming
 What are analogous structures? Analogous structures
carry out the same function but differ in their
structure. Ex: Fin of a fish & flipper of a whale.
The wing of a bird & the wing of an insect are analogous
structures; why? Both enable the organism to fly, but
one is made of membranes & the other of bone.
e. Biochemistry
 Scientists compare the amino acids, proteins, DNA &
RNA of different organisms.
 The more similar the amino acids, proteins, DNA & RNA
of the different organisms are the more closely related
they are.
 Look at Figure 10 on page 384; which 2 organisms are
we most closely related to? The gorilla & Rhesus
monkey
How do you know? They have only 1 & 8 differences in
the amino acids of their hemoglobin when compared
with ours.
C. Evaluating Darwin’s Ideas
1. What were 3 major strengths of Darwin’s work?
a. Gathered evidence of evolution
b. Presented a mechanism for evolution
c. Realized that variation is important
2. What was the one weakness in Darwin’s explanation for evolution
through natural selection? He couldn’t explain how inheritance
took place.