Honors Biology
Lesson Notes 2
Unit 11 - Biological Evolution
Lesson Objectives: You will:
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understand the terms hypothesis and theory.
state Lamarck's law of use and disuse and law of inheritance of acquired characteristics.
explain why it is not possible for organisms to inherit acquired characteristics.
give lines of evidence that led Darwin to conclude that organisms evolve.
explain what is meant by natural selection and use it to explain an example of evolutionary change.
compare and contrast explanations of change given by Lamarck and Darwin.
VII. Lamarck's View
A. The year was 1809 and a French naturalist named Jean Baptiste de Lamarck had something to say on
evolution--an elusive concept at the time. What he said is now called Lamarckism. Although many of
his ideas were wrong, he was on the right track.
B. He formulated two major hypotheses . They were:
1. The Law of Use and Disuse - characteristics could be obtained or lost as a result of use or
disuse.
2. Inheritance of Acquired Characteristics - acquired characteristics are passed on to
offspring.
C. Of course, modern genetics fails to support Lamarck's assumptions. It is easy for today's students of
biology to recognize the reasons why.
D. For instance, Lamarck would have explained the evolution of a giraffe's long neck with the following
statement: Giraffes have evolved long necks because food was much more plentiful in the tops of trees
where competition was less so they stretched their necks to reach it. Therefore, the longer neck was
passed on to successive generations. He had the right idea, but the wrong method to explain it.
E. Is there any experimental evidence to refute Lamarck's claims? Yes. In one experiment, mice tails
were removed for over twenty generations. We hypothesize that if the tails of mice are removed, then
their offspring will also lack tails. However, each succeeding generation of mice was born with tails.
There are many other such examples.
F. Lamarck's hypotheses and parts of his theory have been rejected, but that does not explain away
evolution.
G. Here is a summary of Lamarck's views. He believed:
1. each species is created with a god-given drive toward perfection that, combined with
environmental factors, impelled it along a relentless journey up the ladder of life.
2. the production of new organs or structures resulted from perceived needs.
3. if an organ is used constantly it will tend to become highly developed, whereas disuse results
in degeneration.
4. characteristics acquired over a life time were passed on to offspring.
VIII. Ideas that Influenced Darwin
A. By the 18th century religious dogma had been challenged by many scientists:
1. Astronomers argued that the earth was not the center of the universe.
2. The geologist Hutton maintained that the earth was very ancient with "no vestige of a
beginning - no prospect of an end".
B. In 1830 the geologist Lyell published Principles of Geology, which greatly influenced Charles
Darwin in formulating his theory of evolution.
1. Lyell maintained that the earth was hundreds of millions of years old and that the mountains,
valleys, rivers and coastlines were not created by Noah's flood but by the ordinary action of
rains, winds, earthquakes, volcanoes and other natural forces.
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2. He put forth three principles that constitute the theory of uniformitarianism:
a. natural laws are constant in space and time.
b. scientists should attempt to explain events of the past through the same sorts of
natural processes that we can observe directly today.
c. most geological change occurs slowly and gradually, not through sudden catastrophic
events.
C. By 1830 most scientists believed that the earth was old and that the structure of the earth had changed
substantially over time.
D. Fossils presented a special problem for biologists. As more and more preserved remains of plants and
animals were found, it became impossible for them to deny that fossils represented extinct organisms.
E. However, Cuvier developed the theory of Catastrophism to explain the existence of fossils.
2. He maintained that all organisms were created at once but that periodic catastrophes wiped
many out.
3. Areas were repopulated by the survivors.
IX. Darwin’s Theory
A. Charles Darwin (1809-1882) was an Englishman who spent two years in medical school at Edinburgh
and then trained as a clergyman at Cambridge for three years.
1. He was mostly bored by his studies but while at college he became friends with some of the
most respected scientists of the time.
2. Through a college contact he accepted an unpaid post as naturalist aboard the HMS Beagle
which sailed around the world for 5 years (1831-1836).
B. When Darwin left England he believed the church dogma of special creation as told in Genesis.
However, his observations over five years led him to question it.
C. Darwin took along Lyell's just published Principles of Geology which challenged belief that the earth
was created by divine plan only 6,000 years ago.
1. He was impressed by Lyell's emphasis on the great antiquity of the earth's rocks and he
gradually began to think that the characteristics of organisms as well as the face of the earth
could change over time.
D. Darwin got off the ship wherever possible and he collected specimens and took notes on virtually
every fossil and living organism he encountered. These observations sowed the seeds of his theory of
evolution.
1. Darwin was amazed by the variety of organisms he encountered during his voyage.
Everywhere he looked, he saw new and oddly shaped trees, exotically colored flowers and
birds, and beetles and other insects.
E. Darwin quickly realized that the diversity of living organisms was only part of the mystery of life. He
found even greater numbers of fossil species.
1. In Argentina, he discovered fossil armadillos, giant ground sloths, peculiar horses, and
creatures that reminded him of the hippopotamus.
F. Darwin soon became convinced that living organisms (extant) were vastly outnumbered by extinct
forms.
1. He was convinced that extinction and the appearance of new species were real phenomena
that had to be explained.
2. Fossils of giant armadillos and sloths caused him to think that although they belonged to
extinct forms, they were constructed on the same basic plan as the small extant species of the
region.
3. This started him thinking of a fossil sequence of animal species through the ages and the
causes of extinction. He realized that living species have ancestors.
G. Darwin also noted that organisms differed markedly from continent to continent and on opposite sides
of natural barriers such as mountains, deserts, and large rivers.
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On traveling from north to south in South America he observed that one species was
replaced by similar, but slightly different species. For example, he noted the differences in
ostriches from area to area.
2. He couldn't imagine that several minor versions of species would be created separately, one
for each locality.
3. He concluded that not only did species change through time, but also they changed with
geographical distance.
4. Darwin wrote in his journal "it was evident that such facts could only be explained on the
supposition that species gradually became modified; and the subject haunted me".
Darwin also witnessed the forces of geology in action.
1. He saw the eruption of a volcano in Chile and later learned that another volcano 500 miles
away had blown its top the same night.
2. He also experienced an earthquake that lifted beds of marine mussels "still adhering to the
rocks, ten feet above the high water mark".
3. He observed beds of fossil marine organisms thousands of feet above sea level and he began
to understand how the Andes Mountains were formed by uplift.
4. His belief in geological uniformitarianism was strengthened.
Throughout his journey, Darwin marveled at the "perfection of structure" that made it possible for
organisms to do whatever they needed to do to stay alive and produce offspring.
1. He called this perfection of structure fitness, by which he meant the combination of all traits
that help organisms survive and reproduce in their environment.
2. Darwin also began to question what process had "fit" these organisms to their physical
environments and to each other.
Darwin's visit to the Galapagos Islands, a cluster of rugged volcanic islands only a few miles apart,
600 miles west of Ecuador had the most profound impact on his thinking.
1. Darwin noted that these islands were inhabited by a surprising number of bizarre and often
beautiful plant and animal species.
2. He surmised correctly that many of these species were endemic (found nowhere else).
Later in his journals Darwin wrote about the Galapagos Islands: "Considering the small size of these
islands we feel the more astonished at the number of their aboriginal beings, and their confined
range. Seeing every height crowned with its crater, and the boundaries of most lava-streams still
distinct, we are led to believe that within a period geologically recent the unbroken ocean was here
spread out. Hence both in space and time, we seem to be brought somewhat near to that great factthat mystery of mysteries-the first appearance of new beings on this earth".
Darwin noticed that although the tortoises were clearly different from island to island they not only
all resembled each other but they also resembled those of the mainland. This was also true for a group
of small birds now called Darwin's Finches.
1. In both cases he reasoned that an ancestral stock had migrated to the islands where they
underwent profound changes under the different conditions of the individual islands.
2. Apparently a single ancestral group could give rise to several different varieties or species.
When Darwin left England in 1831 he accepted the religious dogma of special creation. On his return
to England in 1836 he was convinced of the idea of "descent with modification", i.e. all organisms,
including humans, are modified descendants of previously existing forms of life.
Darwin thoughts developed in two stages:
1. the realization that organisms are not fixed and unchangeable.
2. to provide an explanation of the process of evolutionary change.
Darwin spent the next 20 years formulating his theory while also working on a number of other
scientific projects.
1. Darwin became interested in the domestication of plants and animals and how breeders
artificially select different varieties of dogs, horses, fowl and crop and ornamental plants from
one species.
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2. The breeders had only vague notions as to the origin or inheritance of the variable traits.
3. Darwin acknowledged the unlimited variability in organisms but was never able to explain
satisfactorily how a variant trait was inherited. [Recall that Mendel was a contemporary but
his work was somehow overlooked until 1900].
In 1837 Darwin wrote "how [artificial] selection could be applied to organisms in a state of nature
remained a mystery to me".
In 1838 Darwin read Essay on the Principle of Population by a mathematician named Thomas
Robert Malthus.
1. Malthus maintained that human population increases geometrically yet the means of
sustenance increase arithmetically. He claimed that sometime in the future human population
growth would exceed resources and there would be intense competition causing war, misery
and famine.
2. From this Darwin concluded that competition exists among all living things and a "struggle
for existence" might be the means by which well adapted individuals survive and the ill
adjusted are eliminated.
3. Darwin realized that perpetual selection existed in nature in the form of natural selection. In
contrast to artificial selection, the breeder is replaced by conditions in the environment that
prevent the survival and reproduction of certain individuals.
4. Natural selection occurs without a conscious plan or purpose.
In 1858, while Darwin was working on his manuscript outlining his theory of evolution, he received a
manuscript for review by a young English naturalist named Wallace. The title was On the Tendencies
of Varieties to Depart Indefinitely from the Original Type. To Darwin's surprise Wallace had
independently come up with the same theory of natural selection!
1. Wallace was a naturalist working mostly in the Malay Archipelago.
2. He had also read Essay on the Principle of Population by Malthus and it came into his mind
during a malarial fever. He wrote..."suddenly there flashed upon me the idea of survival of
the fittest".
Darwin wanted to let Wallace publish first but Lyell convinced him that they should jointly present
their work. Papers by both Darwin and Wallace were read before the Linnaean Society of London on
July 1, 1858.
Lyell urged Darwin to publish his full theory of evolution as soon as possible. On the Origin of
Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for
Life (also known as Origin of Species) was published and sold out on Nov. 24, 1859.
Both Darwin and Wallace share credit for the theory of natural selection, however there is
much more to the theory of evolution than this. Over more than 20 years Darwin amassed massive
amounts of meticulously documented evidence to support his theory of "descent with modification"
which can be summarized as follows:
1. All species reproduce in excess of the numbers that can survive.
2. Yet adult populations remain relatively constant.
3. Therefore there must be a severe struggle for survival.
4. All species vary in many characteristics and some of the variants confer an advantage
or disadvantage in the struggle for life.
5. The result is a natural selection favoring survival and reproduction of the more
advantageous variants and elimination of the less advantageous variants.
C. Pace
These notes are revised from lecture notes written in 1997 by Chuck Pace for his A.P. Biology students that were
themselves based on lecture notes originally published on the World Wide Web at
<http://arnica.csustan.edu/biol1010/Evolution/evolution.htm> by Dr. Steven J. Wolf of California State University
Stanislaus.
C. Pace