Download The modern day view of evolution again is a result of contribution of

Performance Benchmark N.12.B.4
Students know scientific knowledge builds on previous information. E/S
The modern day view of evolution is a result of contributions of many scientists over many
centuries. While mankind has long wondered why there is such diversity on our planet, we can
begin our journey with Aristotle (384-322 BC). Aristotle is often credited with the idea of a
“ladder” or “scale of nature”. This view held that life was organized from the less perfect to the
nearly perfect state. Positioned at the bottom were plants progressing through invertebrates until,
at the top of ladder humans were positioned. This idea survived for many centuries.
In the17th century the Judeo/Christian world view held that life was a result of God’s creation.
This belief held that the Earth was the center of the universe and was, according to Bishop James
Ussher, created in 4004 BC. Furthermore, man had been on Earth since the beginning of time.
For a detailed account of Ussher’s calculations on the age of Earth, go to
http://www.lhup.edu/~dsimanek/ussher.htm
However while people looked to organized religion for answers to anything scientific, several
astronomers began to look at the real world to develop scientific answers. Nicolas Copernicus
(1473-1543) and Galileo Galilie (1564-1642) though numerous observations of the planets,
moons and our sun began to dispute the idea of an Earth-centered universe and religious answers
to things scientific.
After Galileo, Nicolaus Steno (1642-1686) began to look at the Earth itself in a new way. In the
past, the existence of fossils and the layering of rocks had been explained as the result of a series
of floods and extinction events. Steno stated the laying of rocks or stratigraphy was a result of
natural causes and could be interpreted as a sequential record of the Earth’s past. Today this is
referred as the Principles of Superposition and Cross Cutting Relations. For greater detail about
these geologic concepts see TIPS Benchmark E.12.C.1
Figure 1. Nicolaus Steno.
(from http://www.nndb.com/people/070/000097776/nicolaus-steno-1-sized.jpg)
Figure 2. The illustration done by Steno represents what was commonly know in his day
as “dragons teeth”. Steno wrote that these were examples of fossilized shark’s teeth.
(from http://upload.wikimedia.org/wikipedia/commons/thumb/4/45/Steno_shark.jpg/180px-Steno_shark.jpg)
At the same time John Ray (1628-1705), who along with Carlos Linnaeus (1707-1778) helped to
establish our modern system of classification saw “species” as the basic unit in classifying living
organisms. Yet, Ray was not convinced that fossils were remains of once living organisms,
believing that organisms have remained “unchanged since creation”. On the other hand Linnaeus
did recognize the fossil record, but also believed in a special creation.
In the 1700’s the primary view of life on Earth still held that the Earth was young, being less
than 6000 years old, and that life had been created by God. In addition life was organized in a
hierarchy with man occupying the top of this scale of nature. At this time several French
scientist began to look for other answers. Comte de Buffon (1707-1788) began to lay the seeds
for a new view. In his 44 volume encyclopedia of the natural world entitled the Historie
Naturelle, Buffon discussed the similarities of humans and apes and even talked about a common
ancestry between the two. He believed in organic change amongst living organisms, but has no
mechanism to explain this change, yet suggested the importance of the environment’s influence
in this change. He also supported the idea that the fossil record is a record of past life on our
planet revealed in his quote;
“We have monuments taken from the bosom of the Earth, especially from the
bottom of coal and slate mines, that demonstrate to us that some of the fish and
plants that these materials contain do not belong to species currently existing.”
In a later publication (Les Epoques de la Nature – 1788) Buffon talked about concepts relating to
the Earth that point to a much older origin, that is, the Earth maybe up to 75,000 years old. Forty
years after Buffon’s death some of these concepts appear in the Charles Lyell’s works on the
principle of uniformitarianism.
Georges Cuvier (1769-1832), oftentimes referred to as the “Father of Paleontology”, supported
the idea that the fossil record does represent change over time, but still believed in natural
(unexplained, but not biblical) causes for this change. While Cuvier preferred to use the term
revolutions (often widespread floods) for these changes, this idea became later know as
Catastrophism. Cuvier stated that these geological revolutions caused the extinction of fixed
species, which were later, replaced by new species that migrated from elsewhere. Where that
“elsewhere” was, Cuvier could never explain. He could not also explain the origin of modern
living organisms not represented in earlier fossil records. While he did not support the ideas of
common ancestry amongst organisms, Cuvier did develop the comparative method of studying
organisms.
Cuvier’s revolutions were later replaced by concepts of uniformitarianism. And today, the idea
of catastrophes does reemerge in valid hypotheses that have explained the disappearance of the
dinosaurs in the Cretaceous Extinction Event and the reduction of the amphibians in the Permian
Extinction Event.
For more on Cuvier, go to
http://www.ucmp.berkeley.edu/history/cuvier.html
After Cuvier’s death Louis Agassiz (1807-1873) demonstrates that Cuvier’s floods were actually
evidence of glacial deposits throughout Europe.
For more on Agassiz, go to
http://www.ucmp.berkeley.edu/history/agassiz.html
The first biological theory of evolution was put forth by Jean Baptiste Lamarck (1744-1829).
Lamarck wrote that “time and favorable conditions in nature can produce change.” Lamarck
proposed two mechanisms that produced change in biological organisms over time and that the
environment played an integral role in this change. First he supported the Aristotelian view that
the change in life on Earth followed a progression from the simple to the complex. Lamarck
proposed that an inherent striving (or inner needs of organisms) helped an organism adapt to
changing environments. Lamarck also proposed that changes in organisms were brought about
by the use or disuse of body parts.
Because of an inner need to find food giraffes found it necessary to reach higher and higher into
trees for leaves. This resulted in the “stretching” of their necks over their life times. These longer
necks in turn were passed down to their offspring, that is, the characteristics acquired during the
life time of an individual giraffe were passed on to their offspring. Today we know that acquired
characteristics cannot be passed on to offspring, but Lamarck’s emphasis on the environment
was to be replayed later.
In 1795, James Hutton (1726-1797) wrote his book titled Theory of the Earth. Here Hutton
argued against the principle of catastrophism and introduced the principle of uniformitarianism.
This theory provided for a continuing, gradual change of the Earth over long periods of time by
similar forces (wind, rain, erosion, volcanic action) that are still acting on the Earth today. In
particular the phrase in his book “no vestige of a beginning, no prospect of an end” is interpreted
today by geologist as meaning that the Earth is very old.
Figure 3. James Hutton.
(from http://www.usgs.gov/aboutusgs/images/collections/575005.jpg)
Figure 4. Hutton’s unconformity at Jedburgh Scotland published in the “Theory of the Earth” in 1795.
(from http://www.artsci.wustl.edu/~landc/html/gould/gould1.jpg)
By the beginning of the 1800s geologists began to develop the Geological Timetable. In
England, canal engineer William Smith (1769-1839) discovered that different rock formations
contain distinct fossil assemblages and that even isolated areas of rocks could be identified in the
sequence by the fossils that they contained. This idea is known as the Principle of Biotic
Succession.
Figure 5. A simplified version of the geological time scale.
(from http://www.dep.state.fl.us/geology/images/time_scale_final2.jpg)
Thus by the early 1800s scientists had proposed that life on Earth had changed over time and
these changes were due to natural causes. Yet, while mechanisms were being proposed for the
physical change of the Earth, accepted mechanisms for the change of living organism still eluded
scientists. But this was about to change.
In England a young Charles Darwin had just graduated from college with a degree in theology,
but looking beyond a career as a country clergyman. To Darwin’s fortune he was offered a
position of a captain’s gentlemen companion and naturalist aboard a British naval surveying ship
called the HMS Beagle which he accepts. This five year voyage (1831-1836) provided Darwin
with experiences and evidence that produced our current basic understanding of biological
evolution.
To learn more about Darwin’s voyage on the HMS Beagle, go to
http://www.aboutdarwin.com/index.html\
After Darwin’s return he began to review his notes and embarked on the task of trying to explain
what he saw on this voyage. The result is his theory of natural selection. However, this theory
was not Darwin’s alone, as influences by the other writers can be seen in his ideas.
During his voyage Darwin had the chance to read several books including those of Charles Lyell.
Charles Lyell (1797-1875) was able to popularize Hutton’s theory of uniformitarianism in his
1830 book entitled Principles of Geology. In this book Lyell emphasized that the geological and
biological changes that have occurred on Earth were due to ordinary, natural causes. Natural
laws are constant in space and time. Thus one can explain the past by observing the present. In
addition Lyell stated that this change was gradual, not sudden and without the help of
catastrophes. His ideas also implied that the Earth was very old, that is, millions of years old.
Darwin stated later in life, “I feel as if my books came half out of Sir Charles Lyell’s brain.”
Figure 6. Charles Lyell.
(from http://www.mnsu.edu/emuseum/information/biography/klmno/images/lyell_charles.jpg)
Learn more about Charles Lyell at
http://www.victorianweb.org/science/lyell.html
Two years after his return Darwin read the book Essay on the Principles of Population written by
Rev. Thomas Malthus in 1789. In this book Malthus explained how environmental factors and
particular food supply helped to keep populations in check. In these writings we find the origin
of two observations in Darwin’s theory of natural selection. Malthus states that a “struggle for
existence” occurred amongst members of a species as they competed for food which limits
growth; and “variations within species” might lead to survival advantages amongst its members.
Figure 7. Thomas Malthus.
(from http://www.d.umn.edu/cla/faculty/troufs/anth1602/images/Malthus-TURN80208.jpg)
To learn more about Thomas Malthus, go to
http://www.ucmp.berkeley.edu/history/malthus.html
By 1839, Darwin had the essential elements of his theory, and by 1844 had it outlined in
a 230 page essay, but was reluctant to publish for fear of the public’s reactions to his ideas and
the subsequent effects on this family. However all of this changed when he received a letter from
Alfred Russel Wallace (1823-1913) in 1858. Wallace had been working in Indonesia and had
read Lyell and Malthus along with various natural history papers of Darwin’s. He was now
writing to explain his ideas on evolution to Darwin. In his letter he writes “....it suddenly flashed
upon me that.....in every generation the inferior would inevitably be killed off and the superior
would remain--that is, the fittest would survive.”
Darwin realized that Wallace had independently developed similar ideas to his theory of natural
selection. With advice from friends, Darwin finished his book and in 1859 On the Origin of
Species by Means of Natural Selection was published. The scientific world soon realized that
there is now presented a viable mechanism to explain how organisms change over time.
To learn more about Darwin’s theory of natural selection to go TIPS Benchmark L.12.D.6
However Darwin’s theory was not complete. In order for his “gradualism” to work the Earth
needed to be old and he needed to provide a mechanism to explain how organisms inherited the
advantageous traits that allowed their parents to survive. These were to come during the next 50
years.
Advances in radiometric dating by the early 1900s established that Earth was billions of years
old giving Darwin’s gradualism more than enough time to occur. But the idea of gradualism was
modified in the 1970s with the introduction of punctuated equilibrium by Neils Eldridge and
Stephen Gould. These two proposed that evolution could proceed relatively quickly at times,
geologically speaking. They pointed to the fact that various extinction events including the
Cretaceous Extinct Event brought about a “quick” demise of some living groups and rise to
others. In this case the demise of the dinosaurs accelerated the rise of the birds and mammals.
To learn more about punctuated equilibrium, go to
http://www.pbs.org/wgbh/evolution/library/03/5/l_035_01.html
In 1865, Gregor Mendel published his concepts of inheritance which form the basis of modern
genetics. In the 1920s biologists put Darwin’s theory of natural selection and Mendel’s concepts
of inheritance together and developed what is known as the Modern Synthesis. Darwin now had
a mechanism which would explain how favorable traits were passed from one generation to the
next.
In the early 1900’s the Hardy-Weinberg Principle was developed to explain change in gene
frequencies within populations. Today biologist no longer view evolution as just the physical
change in organisms over time, but the change in gene frequencies within populations over time.
To learn more about how gene frequencies change over time visit TIPS Benchmark L.12.D.5
Although Darwin’s theory of natural selection formed the basis of our current scientific views on
evolution, its ideas and origin come from many scientists both before and after him. To
summarize;
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It began with Copernicus and Galileo’s ideas of the universe, with their position that one
could only find the explanations for nature in nature and not in the supernatural.
Later Ray and Linnaeus established species as a viable entity in nature.
Steno, Buffon and Cuvier demonstrated that life on our planet had changed over time
with the establishment of the fossil record as a natural event.
With the development of the theory of uniformitarianism, Hutton and especially Lyell
wrote that changes in geology and biology are natural and have been occurring since the
beginning of time.
The Earth was “made old” with the establishment of radiometric dating.
Mendel provided Darwin with a mechanism to explain the inheritance of traits.
Hardy and Weinberg provide a mathematical model to explain gene frequencies changes.
Support and refinement for the theory of evolution continues today with the discovery of new
fossils and the addition of DNA evidence. If the basic tenets of the theory of natural selection
and evolution are to be further refined or changed, then it will depend upon new evidence and
new ideas that will be an effort my many scientists over time and space.
View these websites for development of evolutionary theory and natural selection support;
Charles Darwin and His Writings
http://www.sc.edu/library/spcoll/nathist/darwin/darwinindex.html
View the History of Evolutionary Thought at http://www.mnsu.edu/emuseum/biology/evolution/
Read about Darwin’s Precursors and Influences at The Talk Origins Archive
http://www.talkorigins.org/faqs/darwin-precursors.html
Continental Drift of the Theory of Plate Tectonics
When one views a map of the Earth, one can’t help but wonder if the continents are like pieces of
a gigantic jigsaw puzzle that have been pulled apart. This idea actually goes back to the sixteenth
century when the first accurate maps of the world began to appear. The idea can be found in
Novum Organum (1620) by Francis Bacon when he commented on the similar shapes of Africa
and South America. Even earlier the Dutch map maker Abraham Ortelius, who in 1596
suggested that the Americas were “torn away from Europe and Africa….by earthquakes and
floods”. Again he noticed the similarities of the coastlines between these continents.
Figure 8. This is a drawing done by geographer Antonio Snider-Pelegrini in 1858
shows how South America and Africa could have been joined.
(from http://pubs.usgs.gov/gip/dynamic/historical.html)
Figure 9. Today we see that the continents fit together best when edges of the continental
shelves are taken into account. This data was not available to Wegener.
(from http://www.calstatela.edu/faculty/acolvil/plates/jigsaw.jpg)
In 1911, a young Alfred Wegener was browsing in a university library and came across a
scientific paper that intrigued him. The paper showed that identical plants and animals were
found on both sides of the Atlantic. Popular ideas at the time believed that land bridges, now
sunken could explain these occurrences. But like others earlier, Wegener noticed the closeness of
fit between the coastlines on each side of the Atlantic and began to search for a different
solution. In 1915, Wegener proposed a theory in the book The Origin of Continents and Oceans
that attempted to explain how these continents were pulled apart. He called his theory continental
drift. While others had proposed similar ideas in the late 1800’s, Wegener’s idea was the first
catch the wide spread attention of other scientists. In this book Wegener attempted to support his
theory from several areas of science, yet scientists attacked his theory because it lack the
necessary data and mechanism to explain how the continents could possibly drift over the Earth’s
surface. As a result his theory was relegated to the backwaters of science, but slowly over the
next five decades the data and the mechanism were uncovered that would support his theory.
At the beginning of the 1900’s, scientists were now able to over turn the Earth/age limiting ideas
that were proposed by Lord Kelvin. Yet what was known about the earth sciences seemed to rest
on pretty solid ground, anything new was looked upon with suspicion. Rollin T. Chamberlin, an
America geologist at an A.A.P.G symposium in 1928, stated “If we are to believe in Wegener’s
hypothesis we must forget everything which has been learned in the last 70 years and start all
over again.” As Wegener was not a member of any professional geological organizations, his
ideas were not given much credence. Bailey Willis, another American geologist called it a “fairy
tale”. As an “outsider”, Wegener’s ideas were not well received by mainstream geologists.
What may have “allowed” scientists like Wegener to view a changing Earth goes back to the idea
of uniformitarianism first developed by James Hutton in 1785 and further supported by Charles
Lyell in 1835. This idea essentially states that the present is the key to the past. This view of the
Earth assumed that the geological forces and processes that are acting on the Earth today were
the same forces acting on the Earth in the past. These geological forces could be the answer as to
how the continents drifted apart in the past and continue to drift apart today.
Wegener presented geological, paleontological, and paleoclimatic evidence supporting
continental drift which can be reviewed in greater detail at TIPS Benchmark E.12.C.2
To illustrate Wegener’s thinking let’s look at one piece of evidence, that of the fossil
Glossopteris. This organism is a fern that dates back to coal beds which were formed some 250
million years ago in the late Paleozoic era. This fossil fern is found in several southern
continents. If the continents had been fixed and had not moved, some connection between these
continents must have existed. A land bridge (Central America) connects North and South
America, why not South America and Africa? Wegener saw no possible support for this idea and
continued to assume that the continents were once joined, but what mechanism resulted in their
separation. It was this lack of a mechanism that lead Rollin T. Chamberlin to say in 1928, “Can
geology still call itself a science, when it is possible for such a theory as this to run wild?”
Figure 10. A fossil leaf from the tree Glossopteris
http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/tectonics_landforms/tectonics_evidence.html
To learn more about the fossil Glossopteris go to:
http://www.glossopteris.com/what_is_a_glossopteris
Figure 11. Similar layer of rock found in Antarctica, Australia, South America, Africa and India
before the breakup of Pangea. Glossopteris is found in this rock layer on all these continents.
(from http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/tectonics_landforms/tectonics_evidence.html)
Figure 12. Distribution of several plant and animal fossils found in the continents that formed in
Gondwanaland, the southern portion of the super continent known as Pangaea.
(from http://earthobservatory.nasa.gov/Library/Giants/Wegener/wegener_4.html)
Figure 13. Distribution of mesosaurus fossils in South America and Africa.
(from http://www.calstatela.edu/faculty/acolvil/plates/mesosaurus.jpg)
Note in 1991 the first meat-eating dinosaur, Cryolophosaurus was discovered in Antarctica in
Jurassic sediments. The location was about 400 miles from the South Pole. This is a further
indication that Antarctica had been in a tropical environment at one time and has since moved to
its present location.
More on this dinosaur can be found at
http://www.answers.com/topic/cryolophosaurus
To learn more about Alfred Wegener and his ideas, go to
http://www.ucmp.berkeley.edu/history/wegener.html
Despite the great opposition, Wegener did have his supporters. In 1928, Arthur Homes had
postulated the idea of thermally driven convection currents within the Earth. These currents
would provide a mechanism for Wegener’s drifting continents. Nevertheless while the idea was
essentially correct it was not helpful as there was no explanation as to how these currents could
move the continents.
At the same time in South Africa, Alex du Toit, a field geologist noted a remarkable similarity
between the Paleozoic and Mesozoic geology of South Africa and eastern portions of South
America. Toit became a supporter of Wegener. Some of this evidence was include in the next
edition of Wegener’s book. Nevertheless by the 1950s there was little support for continental
drift.
While Wegener did make use of some rather obvious geological data he did not realize the
importance of the Mid-Atlantic Ridge which was discovered in the mid-1800s during the laying
of the transatlantic cable. Later other ridges in other oceans were also discovered. More
importantly it was discovered that the hottest and youngest of these ridges were located near the
center lines of these ridges.
Figure 14. The Mid-Atlantic Ridge.
(from http://www.calstatela.edu/faculty/acolvil/plates/atlantic_profile.jpg)
As dating methods became more refined it was discovered that no part of any ocean floor was
found to be older than 200 million years. This is far less than the oldest rocks on the continents
with some continental rocks dating back over 3 billion years in age. Traditionalists were shocked
by this discovery as many believed that the ocean basins and continents had been created at the
same time. In addition three other important pieces of information were found, 1) the material
forming the continental crust was different from the ocean crust, 2) the ocean crust was much
thinner, and 3) a denser material underlies both ocean crust and continental crust.
Further work on the magnetic orientation of the seafloor rock exposed an interesting pattern.
Readings by magnetometers towed across the Atlantic found a somewhat equal symmetry on
both sides the midline of the Atlantic Ridge. Researchers found alternating bands of polarity on
both sides of the ridge. The exact meaning of this pattern was not immediately clear, but it was
soon to come.
Figure 15. Alternating patterns of polarity along the Mid-Atlantic Ridge.
(from http://www.calstatela.edu/faculty/acolvil/plates/seafloor_formation.jpg)
Modern day support for continental drift was to come from Harry H. Hess in 1960. Hess
proposed that magma rises from the Earth’s depths along the centerline of the mid-ocean ridge.
This rising magma forms the mountain ranges of the oceans and the magma spreads out in two
opposite directions away from ridges. It was discovered that regions of volcanic activity
corresponded to the edges of the proposed tectonic plates.
Figure 16. World map of tectonic plates.
(from http://www.geog.nau.edu/courses/alew/ggr346/text/maps/rof.gif)
Further support came when scientists realized the patterns of polarity in the seafloor represented
fossilized evidence of the Earth’s changing magnetic field. Scientist knew that the Earth has
reversed its magnetic field numerous times during Earth’s long history. The ocean floor
represented a fossil record of those changes over the past 200 million years. Magnetic bands
nearer the center were younger than magnetic bands further from the center. It seemed obvious
that portions of the Earth’s surface were moving. Hess’s idea became known as seafloor
spreading. It also seemed that this would provide the mechanism Wegener needed to explain how
the continents drifted. Hess wrote, “The continents do not plough through oceanic crust impelled
by unknown forces, rather they ride passively on the mantle material as it comes to the surface at
the crest of the ridge and then moves laterally away from it.”
Figure 17. Ages of the ocean floors of the world.
(from http://pubs.usgs.gov/of/1999/ofr-99-0132/image115.gif)
As scientific knowledge about the Earth was building on previous and newly acquired
knowledge, a new idea was developing called Plate Tectonics. This view put forward the idea the
Earth’s crust was divided into a number of ridge plates and while these plates vary in thickness
between the oceans and continents they are all floating on a plastic layer called the
asthenosphere. In this theory plate movement is driven by powerful currents of molten rock
within the plastic-like asthenosphere. This new evidence provided a mechanism that caused the
continents to move or in Wegener’s words “drift”.
Yet questions still remain. The powerful currents of molten rock seem able to explain the
movements of the continents, but they do not adequately do so for the ocean crust. Research
continues to reach a greater understanding of what is happening as the Indian Plate collides with
the rest of Asia. Questions about the size of plates and their numbers continue to spawn further
research in this area.
To learn more about evidence used to support the idea of Plate Tectonics, go to
http://pubs.usgs.gov/gip/dynamic/developing.html
To learn how plate tectonics continues to change our Earth see The Dynamic Earth online at
http://www.mnh.si.edu/earth/text/index.html
More can be found at the PBS website Mountain Make, Earth Shaker at
http://www.pbs.org/wgbh/aso/tryit/tectonics/#
Performance Benchmark N.12.B.4
Students know scientific knowledge builds on previous information. E/S
Common misconceptions associated with this benchmark.
1. Students incorrectly assume that scientific laws or theories do not change.
Scientists are observers of the natural world around them. Scientific theory (descriptions of
nature) and scientific laws (explanations or generalizations about a body of observations)
develop as scientists collect data and make observations about the world around them. As we
have seen in the two examples (natural selection and plate tectonics) “new” sets of data or
observations can lead to changing views about the world around us.
2. Students incorrectly believe science is objective and well-scrutinized.
Scientist are human and therefore subject to influences by their cultural surroundings. As in
the case of Wegener and continental drift, his lack of membership in scientific associations
was looked down upon and therefore so were his ideas. Science and scientists are influenced
by history and society like anyone else. They develop prejudices like any other human. These
prejudices can lead to lack of acceptance of ideas.
3. Students inaccurately believe evidence accumulated carefully results in sure knowledge.
The following is taken from the NSTA discussion on the teaching of evolution and illustrates
what is wrong with this misconception.
Q: Some say that evolution cannot be proven because we were not there to see it happen.
How do I respond?
A: Science allows us to study past events and life even though we were not present to observe
them. We know, for example, that ancient cultures existed because we can study artifacts that
have been left behind, and we know where bodies of water used to exist based on the
information we find in the layers of soil and rock, as is currently being done by unstaffed
vehicles on Mars. In addition, scientists are using cosmic microwaves to develop an
understanding of the beginning seconds of the universe's existence. Scientists use the data
from these microwaves to develop basic parameters that characterize the universe, including
its age, geometry, composition, and weight.
As these examples show, data derived by different means are used as evidence to support
scientific theories. It is also important to recognize that scientific theories and laws are subject
to change as a result of new evidence. Thus, the goal of science is not to prove, but to explain.
http://www.nsta.org/publications/evolution.aspx
4. Students incorrectly think that knowledge is static and unchanging.
Misconception #3 illustrates the idea that knowledge in science is not static, but dynamic. As
scientists continue to explore the world around them, new data and observations will lead to
new ideas and new explanations of how our natural world operates or functions. Take the
following example.
In 1885, scientists discovered a plant-growth hormone and called it auxin. Ever since, its
mechanism of action had been a black box, with scientists divided into warring camps about
precisely how the hormone works. Then last week, in a study in Nature, biologist Mark
Estelle of Indiana University, Bloomington, and colleagues reported that auxin links up with a
plant protein called TIR1, and together the pair binds to a third protein that silences growthpromoting genes. The auxin acts like a homing beacon for enzymes that munch on the
silencer. Result: The enzymes devour the silencer, allowing growth genes to turn on. (Wall
Street Journal – 06/03/05)
5. Students incorrectly believe there is always an explanation for everything.
The nature of science is to question and therefore no area of science if free of doubt or debate.
The nature of science is to have unresolved questions. Newton has given us a description (a
law) of gravity, but no one to date has provided a satisfactory explanation of how (a theory)
gravity works. As the cases of evolutionary theory and continental drift show, all the answers
have not fully been realized. In the case of plate tectonics questions such as “When did plate
tectonics begin, and how?”, and “What creates “hotspots” within plates?” still exist.
To learn more about unanswered questions about Plate Tectonics, go to
http://pubs.usgs.gov/gip/dynamic/unanswered.html
6. Students incorrectly think scientific discoveries are always a result of planned
experiments.
As can be seen in the cited examples, neither Darwin nor Wegener started with a planned set
of experiments. Observations of the nature world around them lead to questions. These
questions lead to more observations and possible solutions. Nor did either scientist do actual
experiments in the classical sense of the word. Serendipity has also played a role in a number
of scientific discoveries. Sir Alexander Fleming did not plan to discover penicillin, nor did
Joseph Priestly plan to discover oxygen.
While no single method of scientific discovery exists all scientific discoveries do have certain
common elements whether planned or unplanned. More on this can be explored at
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/S/ScientificMethods.html
and http://www.nap.edu/readingroom/books/obas/contents/social.html
Performance Benchmark N.12.B.4
Students know scientific knowledge builds on previous information. E/S
Sample Test Questions
1. Both Charles Darwin and Alfred Wegener were influenced by previous geological ideas.
Which idea below influenced the thinking of these two scientists?
a) Uniformitarianism
b) Continental drift
c) Catastrophism
d) Global climate change
2. Alfred Wegener used many lines of evidence to support this idea of continental drift. Which of
the following was not used Wegener?
a) Fossil similarities between southern continents.
b) Evidence of magnetic polarity changes in Atlantic Ocean floor rocks.
c) Similarities in the paleoclimates of South America and Africa.
d) The apparent fact the South America and Africa seemed to fit together like a puzzle.
3. Which statement below would best describe the process of science?
a) Scientists are objective and free of prejudice.
b) Scientists generally discover new ideas without the help of others.
c) Scientific ideas evolve or change over time.
d) New ideas in science generally result of planned experiments.
4. While the theory of natural selection describes how organisms change over time, it’s weakness
fails to describe…
a) how the fittest organisms tend to survive over less fit organisms.
b) the role of the environment in evolution.
c) how competition between organism is important to evolution.
d) how organisms inherit their traits from their parents.
5. Which statement below best describes Darwin’s theory of natural selection and Alfred
Wegener’s theory of continental drift?
a) These theories answer all scientific questions about evolution and continental drift.
b) The development of these theories were influenced by many scientists.
c) These theories were a result of a number of planned experiments.
d) These theories are good examples of how scientific theories do not change over time.
Performance Benchmark N.12.B.4
Students know scientific knowledge builds on previous information. E/S
Answers to Sample Test Questions
1. (a)
2. (b)
3. (c)
4. (d)
5. (b)
Performance Benchmark N.12.B.4
Students know scientific knowledge builds on previous information. E/S
Intervention Strategies and Resources
The following list of intervention strategies and resources will facilitate student understanding of
this benchmark.
1. Teaching the Nature of Science sample unit plan
This site is managed by Evolution and the Nature of Science Institutes (ENSI). Students and
teachers can learn more about the process of science by viewing the information, lessons and
resources housed here.
To access resources pertaining to the Nature of Science, visit
http://www.indiana.edu/~ensiweb/lessons/unt.n.s.html
2. Understanding Evolution “your one-stop source for information on evolution”
This site contains a wealth of information pertaining to the history of evolutionary thought,
along with topic discussions relating to how evolution works, how it impacts life, and
supporting evidence for evolution. Articles, Webcasts, and additional classroom resources
are assembled here.
To view resources related to What is the history of evolutionary theory, go to
http://evolution.berkeley.edu/evolibrary/search/topicbrowse2.php?topic_id=48
3. Global Warming and Global Climate Change
Today global warming and climate change are popular topics both in the scientific
community as well as in casual conversations by non-scientific people. Students and teachers
can learn about the history of global warming and global climate change at the following
sites;
The site “Summary of the History of Climate Change Science” provides climate data,
influences, and modeling history of how scientists came to (partly) understand what people
are doing to cause climate change. Access this information at
http://www.aip.org/history/climate/index.html
History of the greenhouse effect and global warming at
http://www.lenntech.com/greenhouse-effect/global-warming-history.htm
Timeline history of the global warming/climate change issue with video and supporting
political climate at http://www.pbs.org/now/science/climatechange.html
4. Global Warming Newspaper Archive
Newspaper articles about global warming tell the story of the Earth's climate and the diverse
opinions and scientific discoveries surrounding the theory of global warming. From the
Industrial Revolution to the Kyoto treaty and the advent of hybrid technology, the topic of
global climate change has enthralled readers and sparked debate for centuries. Though many
people argue over the theory's validity, global warming is a subject that affects us all and
newspapers chronicle its discovery and the debate surrounding the issue.
This site is of particular interest as it serves as an archive of newspaper articles on global
warming with more than 50,000 historical newspaper pages contained and can be accessed at
http://www.globalwarmingarchive.com/Home.aspx