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THEORY OF EVOLUTION PACKET
Part 1: Evidence of Evolution
FOSSILS
Organisms that lived during past eras of the earth’s history have left evidence of their existence.
The remains or traces of such organisms are called fossils. Fossils are usually found in sedimentary
rock. This type of rock consists of particles weathered and eroded from other rock layers. The loose
particles are deposited, generally by water action, and then cemented together by pressure and
chemical activity, forming solid sedimentary rock. There are many types of sedimentary rock,
including shale, sandstone, limestone, and conglomerates.
Types of fossils:
Fossils are preserved in a number of ways. A mold forms when sediments surrounding a
disintegrating plant or animal eventually harden, thus recording the outside form of the organism. A
cast forms when sediments enter a mold and harden. An imprint consists of footprints, tracks, or
tunnels made by animals in soft sediments that eventually harden. Petrification occurs when the
skeletal remains of an animal or the cell walls of a plant are gradually replaced by minerals. The hard
parts of some animals, including shells, teeth, and bones, have been preserved unchanged. Freezing
has preserved complete specimens of the woolly mammoth for many trees, sometimes contains
perfectly preserved insects, Coal, which is formed from the remains of plants, often contains imprints
of leaves and other plant parts.
Radioactive dating of fossils:
The age of fossils may be determined by radioactive dating of the rocks in which they are found.
This process is based on the decay, or transformations, of radioactive elements to more stable elements.
Radioactive elements decay at a steady rate. The half-life of a radioactive element is the time it takes
for half the radioactive atoms in a sample of that element to decay to a stable end product.
There are three types of radioactive dating. Radiocarbon dating uses the radioisotope carbon-14.
Atoms of this unstable isotope disintegrate into stable nitrogen atoms. The half-life of carbon-14 is
about 5,600 years. This method is accurate for dating objects up to 40,000 years old. The potassiumargon method is used on objects that are millions of years old. Radioactive potassium-40 decays into
argon-40 and calcium-40 with half-life of 1.3 billion years. The uranium-lead method can be used for
dating specimens billions of years old. Uranium-238 decays to lead-206 with a half-life of 4.5 billion
years.
Geologic time scale
Before the development of radioactive dating techniques, the history of the earth had been divided
into time periods based on the fossil record. There were three main periods, called eras: the Paleozoic,
Mesozoic, and Cenozoic eras. The Paleozoic began with the sudden appearance in the rock record of a
large variety of life forms, including protists, sponges, jellyfish, corals, segmented worms, insects, and
mollusks among the animals, and mosses, ferns, and gymnosperms among the plants. Fish and
amphibian appeared later in the Paleozoic. The appearance of reptiles was used to mark the end of this
era. The Mesozoic was marked by the dominance of the reptiles, especially the large forms called
dinosaurs. The Cenozoic was characterized by the diversification and dominance of the mammals.
The eras were subdivided into shorter time segments called periods and epochs. The earliest period
in the Paleozoic era was the Cambrian, which began 600 million years ago. Since the age of the earth
is now estimated to be about 6 billion years, most of the earth’s history precedes the Cambrian period.
This time interval is generally called the pre-Cambrian. In recent years there have been many
discoveries of what appear to be microscopic fossils of bacteria and blue-green algae in pre-Cambrian
rocks, some dated to within a few hundred million years of the oldest rocks known.
COMPARATIVE ANATOMY
Many different organisms show similar anatomical structures. Parts of different organisms that
have similar structure, evolutionary origin, and pattern of development are considered to be
homologous. Body parts of different animals that have similar function but are different in structure
and evolutionary origin are considered to be analogous. Homologous structures do not always have
similar functions. Biologists use homologies to indicate relationships between living forms.
Vestigial Organs
Organisms often have structures that serve no useful function but are similar to functional organs in
other organisms. Such structures are described as vestigial. An organ that is vestigial in a living
organism was fully developed and functional in some ancestor of that organism. The presence of such
organs enables biologists to determine past and present relationships between groups of organisms.
Vestigial structures found in humans include the third eyelid (nictitating membrane), appendix, tail
vertebrae (coccyx), and ear muscles.
COMPARATIVE EMBRYOLOGY
Comparing the embryonic development of certain structures in different animals has revealed close
resemblances. In the early stages of development, it is difficult to tell the embryos of different animals
apart. As development progresses, the differences become more apparent. For example, the embryos
of fish, reptiles, birds, and mammals all possess gills, segmentation, and a tail. Such similarities are
taken to be evidence of common ancestry.
COMPARATIVE BIOCHEMISTRY
All living cells show a basic similarity in their chemistry. All cells use ATP in the storage and
transfer energy within the cell. The hereditary information is stored in molecules of nucleic acids. All
living cells contain enzymes. The more closely related two organisms are, the more similar their cell
biochemistry. For example, the hormones produced by the endocrine glands of mammals are all quite
similar. Insulin extracted from cattle, sheep, and hogs is biologically active in humans – that is – it
assists sugar metabolism in humans just as it did in the animal that produced it. This indicates a
relatively close evolutionary relationship.
Part 2: Early Theories of Evolution
Speculations about the history of the earth and the development of life have been made since ancient
times. In the sixth century B.C., Anaximander suggested that men were first formed as fishes, and that
eventually the fish lost their skins and began life on land. In the fifth century B.C., Xenophanes
recognized fossil bones as the remains of ancient animals. Aristotle, in the fourth century B.C.,
thought that there was a gradation in nature from inorganic substances to the most complex living
things. He developed the idea of a phylogenetic tree, or chart.
Lamarck – Theory of Use and Disuse
Jean Baptiste Lamarck (1744-1829) made some important contributions to the theory of evolution.
His theory of need stressed that organisms need to adjust, or adapt, to their environment. When the
environment changes, the organism must adapt or die. Lamarck theorized that organs needed for the
adjustment to environmental stress remained strong and functional, while those not needed gradually
disappeared because of disuse. Finally, Lamarck thought that traits acquired in the course of
adaptation to the environment were passed on to offspring. According to Lamarck, organisms evolved,
or changed, because of alternations in environmental conditions. Such change stimulated the
development of some organs and disappearance of others. Changes in structures that occurred in the
course of adaptation were then passed on to future generations.
DARWIN – THEORY OF EVOLUTION BY NATURAL SELECTION
In 1831, Charles Darwin sailed as a naturalist aboard the British ship HMS Beagle, which was to
explore and chart some Pacific Islands and the coast of South America. The ship visited the Galapagos
Islands, on which finches and huge tortoises lived. Darwin studied these animals and found that
tortoises on different islands displayed different characteristics. The finches also displayed differences
from one island to another, particularly in the structure of the beak. Although the birds were obviously
similar, the beaks differed in size and shape, allowing the birds on different islands to feed on different
types of food. Darwin proposed that the fourteen species of finches on the islands originated from a
common ancestor. Since the islands were separated by stretches of water, the finches were isolated on
islands were separated by stretches of water, the finches were isolated on their respective islands. Thus,
Darwin concluded that the differences between the animals on the various islands resulted from
geographic isolation.
Over the next twenty years, Darwin organized the data from his trip and gathered other information
for his theory of evolution. In 1858, Darwin received a letter from another naturalist, Alfred Wallace,
in which Wallace explained his own theory of evolution. To Darwin’s amazement, Wallace’s ideas
were very close to his own. In a spirit of cooperation, the two men made a joint presentation of their
theory to the Linnaean Society of London.
The theory of evolution by natural selection can be divided into five parts:
1. Overproduction refers to the capacity of every species to produce more offspring than can
survive. In this Darwin was influenced by Thomas Malthus, who theorized that populations increase
at a higher rate than their food supply and that the size of a population is limited by the availability of
food.
2. A struggle for existence results from the competition between organisms for available food,
shelter, and living space.
3. Variations, or differences, between members of a species make every individual different from
every other individual. Variations may be inherited.
4. By the process of natural selection, those members of a species that are best adapted to the
environment will survive loner and reproduce more successfully than individuals that are less well
adapted. Thus, favorable variations will be preserved and unfavorable ones gradually eliminated in
future generations.
5. New species result from accumulated variations in an isolated population. With each generation,
new variations arise that are passed on to the next generation. Eventually, the changes are great
enough that a new species results.
WEISMANN – CONTINUITY OF GERMPLASM
Auguste Weismann, a German biologist, disproved the theory of inheritance of acquired
characteristics. Weismann cut off the tails of mice and then allowed the mice to mate. He repeated
this for twenty generations. The tails of the mice of the twenty-first generation were not affected,
disproving Lamarck’s theory. Weismann explained why acquired characteristics are not inherited in
his concept of the continuity of the germplasm. According to this concept, the body is composed of
two types of cells – somatic, or body, cells, and germ, or reproductive, cells. The somatoplasm
represents all the body cells and the germplasm all reproductive cells, Changes in body cells cannot be
passed on to offspring because these cells are not involved in reproduction. Changes in germ cells,
however, can be passed on to future generations.
DeVRIES – THEORY OF MUTATION
Hugo DeVries, a Dutch botanist, published his theory of mutation in 1901. He based this theory on
investigations of the evening primrose, a flowering plant. During his studies, DeVries noted abrupt,
permanent hereditary changes in plants. He called the changes mutations and concluded that mutations
must occur frequently in other organisms as well. He postulated that mutations were the source of
changes that brought about the development of new species, and therefore, the cause of evolutionary
change.
Name: _____________________________________
Date: ________________ Per:_______
Data Sheet: Theory of Evolution
1. What is a fossil?
2. Most fossils are found in ___________________________________________ rock.
3. In the diagram below, label the rock layers X, Y, and Z, making the X the oldest layer and Z the
youngest.
b. What can you say about the relative ages of the fossils found in each of these layers?
4. The footprints of dinosaurs are an example of a type of fossil called a(n) _____________________.
5. The replacement of the bones of a skeleton by minerals is an example of _____________________.
6. Soft body parts may be preserved for long periods of time by ______________________________.
7. The formation of rock around a dead organism may produce a fossil record called a _____________.
8. Which isotopes are used to determine the age of very old rocks? ____________________________
9. The isotope used in dating of fossils thought to be less than 40,000 yrs old is __________________.
10. The time it takes for half the atoms in a given sample of a radioactive isotope to decay is
___________________________ of that isotope.
11. The half-life of carbon -14 is _______________________________ years.
12. The half-life of uranium-238 is __________________________ years.
13. A science student finds a fossil and submits it for radiocarbon dating. She is told that the fossil
contains ¼ the amount of carbon-14 that it had originally. What is the age of the fossil?
14. In the geologic time scale, the long period of time during which life must have arisen on earth is
the ________________________.
15. The three eras of the geologic time scale are the _____________________, __________________,
and ______________________________.
16. The era that began with the sudden appearance of a wide variety of life forms was the _________
17. What’s the difference between homologous and analogous structures?
18. The diagram below shows homologous structures (forelimbs) from four animals. On each of the
four , label the upper limb bones with an A, the lower limb bones with a B, the wrist bones with a C,
and the digits with a D.
19. How are vestigial structures different from homologous or analogous structures?
20. Three vestigial structures found in modern humans are ____________________,
_____________________, and _________________________.
21. Why is the existence of vestigial structures significant to the study of evolution?
22. What is embryology?
23. What is shown by a similarity in the pattern of embryological development between two different
organisms?
24. Give two examples of biochemical similarities between two different organisms.
25. Why are such similarities considered to be the result of evolutionary relationships?
26. What were the three major concepts in Lamarck’s theory of evolution?
27. The part of Lamarck’s theory that stressed the necessity for organisms to change with their
environment was his theory of _____________________________________________.
28. According to Lamarck’s concept of use and disuse, what happened to organs that were little used?
29. What were Lamarck’s ideas about the inheritance of acquired characteristics?
30. The theory of natural selection was developed independently by two naturalists. These were
__________________________________ and __________________________________.
31. List the major points of theory of evolution by natural selection.
32. Darwin’s concept of overproduction within a species was influenced by _____________________.
33. What did Darwin mean by “natural selection”?
34. What conclusions about the effects of geographic isolation did Darwin draw from his observations
of finches on the Galapagos Islands?
35. How did Weismann disprove the theory of acquired characteristics?
26. According to Weismann, why weren’t acquired characteristics passed on to future generations?
27. What role did Derives think that mutation played in evolution? Was he correct?