Evolution
Evolution is the change in the inherited characteristics of biological populations over successive generations. Evolutionary processes give rise to diversity
at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.[1]
Life on Earth originated and then evolved from a universal common ancestor approximately 3.7 billion years ago.
Repeated speciation and thedivergence of life can be inferred from shared sets of biochemical and
morphological traits, or by shared DNA sequences. These homologous traits and sequences are more similar
among species that share a more recent common ancestor, and can be used
to reconstruct evolutionary histories, using both existing species and the fossil record. Existing patterns of biodiversity have been shaped both by speciation and by extinction.[2]
Charles Darwin was the first to formulate a scientific argument for the theory of evolution by means of natural selection. Evolution by natural selection is a process
that is inferred from three facts about populations: 1) more offspring are
produced than can possibly survive, 2) traits vary among individuals, leading
to differential rates of survival and reproduction, and 3) trait differences
are heritable.[3] Thus, when members of a population die
they are replaced by the progeny of parents that were better adapted to survive and reproduce in the environment in which natural selection took place. This process
creates and preserves traits that are seemingly
fitted for the functional roles they perform.[4] Natural selection is the only known
cause ofadaptation, but not the only known cause of evolution.
Other, nonadaptive causes of evolution include mutation and genetic
drift.[5]
In the early 20th
century, genetics was integrated with Darwin's theory of evolution by natural selection
through the discipline of population
genetics. The importance of
natural selection as a cause of evolution was accepted into other branches
of biology. Moreover, previously held notions about
evolution, such as orthogenesis and "progress" became obsolete.[6] Scientists continue to study various aspects of evolution by forming and testing hypotheses,
constructing scientific theories, using observational
data, and performing experiments in both the field and the laboratory. Biologistsagree that descent with modification is one of the
most reliably established facts in
science.[7] Discoveries in evolutionary biology have
made a significant impact not just within the traditional branches of biology,
but also in other academic disciplines (e.g., anthropology and psychology) and on society at large.[8][9](http://en.wikipedia.org/wiki/Evolution)
Darwin's
Theory of Evolution - The Premise
Darwin's Theory of
Evolution is the widely held notion that all life is related and has descended
from a common ancestor: the birds and the bananas, the fishes and the flowers
-- all related. Darwin's general theory presumes the development of life from
non-life and stresses a purely naturalistic (undirected) "descent with
modification". That is, complex creatures evolve from more simplistic
ancestors naturally over time. In a nutshell, as random genetic mutations occur
within an organism's genetic code, the beneficial mutations are preserved
because they aid survival -- a process known as "natural selection."
These beneficial mutations are passed on to the next generation. Over time,
beneficial mutations accumulate and the result is an entirely different
organism (not just a variation of the original, but an entirely different
creature).
Darwin's
Theory of Evolution - Natural Selection
While Darwin's Theory of Evolution is a relatively young archetype, the
evolutionary worldview itself is as old as antiquity. Ancient Greek
philosophers such as Anaximander postulated the development of life from
non-life and the evolutionary descent of man from animal. Charles Darwin simply
brought something new to the old philosophy -- a plausible mechanism called
"natural selection." Natural selection acts to preserve and
accumulate minor advantageous genetic mutations. Suppose a member of a species
developed a functional advantage (it grew wings and learned to fly). Its
offspring would inherit that advantage and pass it on to their offspring. The
inferior (disadvantaged) members of the same species would gradually die out,
leaving only the superior (advantaged) members of the species. Natural
selection is the preservation of a functional advantage that enables a species
to compete better in the wild. Natural selection is the naturalistic equivalent
to domestic breeding. Over the centuries, human breeders have produced dramatic
changes in domestic animal populations by selecting individuals to breed.
Breeders eliminate undesirable traits gradually over time. Similarly, natural
selection eliminates inferior species gradually over time.Darwin's
Theory of Evolution - Slowly But Surely...
Darwin's Theory of Evolution is a slow gradual process. Darwin wrote,
"…Natural selection acts only by taking advantage of slight successive
variations; she can never take a great and sudden leap, but must advance by
short and sure, though slow steps." [1] Thus, Darwin conceded that,
"If it could be demonstrated that any complex organ existed, which could
not possibly have been formed by numerous, successive, slight modifications, my
theory would absolutely break down." [2] Such a complex organ would be
known as an "irreducibly complex system". An irreducibly complex
system is one composed of multiple parts, all of which are necessary for the
system to function. If even one part is missing, the entire system will fail to
function. Every individual part is integral. [3] Thus, such a system could not
have evolved slowly, piece by piece. The common mousetrap is an everyday
non-biological example of irreducible complexity. It is composed of five basic
parts: a catch (to hold the bait), a powerful spring, a thin rod called
"the hammer," a holding bar to secure the hammer in place, and a
platform to mount the trap. If any one of these parts is missing, the mechanism
will not work. Each individual part is integral. The mousetrap is irreducibly
complex. [4]Darwin's
Theory of Evolution - A Theory In Crisis
Darwin's Theory of Evolution is a theory in crisis in light of the tremendous
advances we've made in molecular biology, biochemistry and genetics over the
past fifty years. We now know that there are in fact tens of thousands of
irreducibly complex systems on the cellular level. Specified complexity
pervades the microscopic biological world. Molecular biologist Michael Denton
wrote, "Although the tiniest bacterial cells are incredibly small,
weighing less than 10-12 grams, each is in effect a veritable
micro-miniaturized factory containing thousands of exquisitely designed pieces
of intricate molecular machinery, made up altogether of one hundred thousand
million atoms, far more complicated than any machinery built by man and absolutely
without parallel in the non-living world." [5]And we don't need a microscope to observe irreducible complexity. The eye, the ear and the heart are all examples of irreducible complexity, though they were not recognized as such in Darwin's day. Nevertheless, Darwin confessed, "To suppose that the eye with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection, seems, I freely confess, absurd in the highest degree." [6]
Footnotes:
1.
Charles Darwin,
"On the Origin of Species by Means of Natural Selection, or the
Preservation of Favoured Races in the Struggle for Life," 1859, p. 162.
2.
Ibid. p. 158.
3.
Michael Behe,
"Darwin's Black Box," 1996.
4.
"Unlocking the
Mystery of Life," documentary by Illustra Media, 2002.
5.
Michael Denton,
"Evolution: A Theory in Crisis," 1986, p. 250.
6.
Charles Darwin,
"On the Origin of Species by Means of Natural Selection, or the
Preservation of Favoured Races in the Struggle for Life," 1859, p.
155.( http://www.darwins-theory-of-evolution.com/)
The (R)Evolution of Theory
The theory of evolution is one of the great intellectual revolutions of human history, drastically changing our perception of the world and of our place in it. Charles Darwin put forth a coherent theory of evolution and amassed a great body of evidence in support of this theory. In Darwin's time, most scientists fully believed that each organism and each adaptation was the work of the creator. Linneaus established the system of biological classification that we use today, and did so in the spirit of cataloguing God's creations.
In other words, all of the similarities and dissimilarities among groups of organisms that are the result of the branching process creating the great tree of life (see Figure 1), were viewed by early 19th century philosophers and scientists as a consequence of omnipotent design.
Figure 1: A phylogenetic "tree of life" constructed by computer analysis of cyochrome c molecules in the organisms shown; there are as many different trees of life as there are methods of analysis for constructing them.
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However, by the 19th Century, a number of natural historians were beginning to think of evolutionary change as an explanation for patterns observed in nature. The following ideas were part of the intellectual climate of Darwin's time.
- No one knew how old the earth was, but geologists were beginning to make estimates that the earth was considerably older than explained by biblical creation. Geologists were learning more aboutstrata, or layers formed by successive periods of the deposition of sediments. This suggested a time sequence, with younger strata overlying older strata.
- A concept called uniformitarianism, due largely to the influential geologist Charles Lyell, undertook to decipher earth history under the working hypothesis that present conditions and processes are the key to the past, by investigating ongoing, observable processes such as erosion and the deposition of sediments.
- Discoveries of fossils were accumulating during the 18th and 19th centuries. At first naturalists thought they were finding remains of unknown but still living species. As fossil finds continued, however, it became apparent that nothing like giant dinosaurs was known from anywhere on the planet. Furthermore, as early as 1800, Cuvier pointed out that the deeper the strata, the less similar fossils were to existing species.
- Similarities among groups of organisms were considered evidence of relatedness, which in turn suggested evolutionary change. Darwin's intellectual predecessors accepted the idea of evolutionary relationships among organisms, but they could not provide a satisfactory explanation for how evolution occurred.
- Lamarck is the most famous of these. In 1801, he proposed organic evolution as the explanation for the physical similarity among groups of organisms, and proposed a mechanism for adaptive change based on the inheritance of acquired characteristics. He wrote of the giraffe:
"We know that this animal, the tallest of mammals, dwells in the interior of Africa, in places where the soil, almost always arid and without herbage, obliges it to browse on trees and to strain itself continuously to reach them. This habit sustained for long, has had the result in all members of its race that the forelegs have grown longer than the hind legs and that its neck has become so stretched, that the giraffe, without standing on its hind legs, lifts its head to a height of six meters."In essence, this says that the necks of Giraffes became long as a result of continually stretching to reach high foliage. Larmarck was incorrect in the hypothesized mechanism, of course, but his example makes clear that naturalists were thinking about the possibility of evolutionary change in the early 1800's.
- Darwin was influenced by observations made during his youthful voyage as naturalist on the survey ship Beagle. On the Galapagos Islands he noticed the slight variations that made tortoises from different islands recognizably distinct. He also observed a whole array of unique finches, the famous "Darwin's finches," that exhibited slight differences from island to island. In addition, they all appeared to resemble, but differ from, the common finch on the mainland of Ecuador, 600 miles to the east. Patterns in the distribution and similarity of organisms had an important influence of Darwin's thinking. The picture at the top of this page is of Darwin's own sketches of finches in his Journal of Researches.
- In 1859, Darwin published his famous On the Origin of Species by Means of Natural Selection, a tome of over 500 pages that marshalled extensive evidence for his theory. Publication of the book caused a furor - every copy of the book was sold the day that it was released. Members of the religious community, as well as some scientific peers, were outraged by Darwin's ideas and protested. Most scientists, however, recognized the power of Darwin's arguments. Today, school boards still debate the validity and suitability of Darwin's theory in science curricula, and a whole body of debate has grown up around the controversy (see the WWW site Talk.Origins for an ongoing dialogue). We do not have time to cover all of Darwin's evidence and arguments, but we can examine the core ideas. What does this theory of evolution say?
Darwin’s theory of evolution entails the following fundamental ideas. The first three ideas were already under discussion among earlier and contemporaneous naturalists working on the “species problem” as Darwin began his research. Darwin’s original contributions were the mechanism of natural selection and copious amounts of evidence for evolutionary change from many sources. He also provided thoughtful explanations of the consequences of evolution for our understanding of the history of life and modern biological diversity.
- Species (populations of interbreeding organisms) change over time and space. The representatives of species living today differ from those that lived in the recent past, and populations in different geographic regions today differ slightly in form or behavior. These differences extend into the fossil record, which provides ample support for this claim.
- All organisms share common ancestors with other organisms. Over time, populations may divide into different species, which share a common ancestral population. Far enough back in time, any pair of organisms shares a common ancestor. For example, humans shared a common ancestor with chimpanzees about eight million years ago, with whales about 60 million years ago, and with kangaroos over 100 million years ago. Shared ancestry explains the similarities of organisms that are classified together: their similarities reflect the inheritance of traits from a common ancestor.
- Evolutionary change is gradual and slow in Darwin’s view. This claim was supported by the long episodes of gradual change in organisms in the fossil record and the fact that no naturalist had observed the sudden appearance of a new species in Darwin’s time. Since then, biologists and paleontologists have documented a broad spectrum of slow to rapid rates of evolutionary change within lineages.
The primary mechanism of change over time is natural selection, elaborated below. This mechanism causes changes in the properties (traits) of organisms within lineages from generation to generation.
The Process of Natural Selection
Darwin’s process of natural selection has four components.
- Variation. Organisms (within populations) exhibit individual variation in appearance and behavior. These variations may involve body size, hair color, facial markings, voice properties, or number of offspring. On the other hand, some traits show little to no variation among individuals—for example, number of eyes in vertebrates.
- Inheritance. Some traits are consistently passed on from parent to offspring. Such traits are heritable, whereas other traits are strongly influenced by environmental conditions and show weak heritability.
- High rate of population growth. Most populations have more offspring each year than local resources can support leading to a struggle for resources. Each generation experiences substantial mortality.
- Differential survival and reproduction. Individuals possessing traits well suited for the struggle for local resources will contribute more offspring to the next generation.
From one generation to the next, the struggle for resources (what Darwin called the “struggle for existence”) will favor individuals with some variations over others and thereby change the frequency of traits within the population. This process is natural selection. The traits that confer an advantage to those individuals who leave more offspring are called adaptations.
In order for natural selection to operate on a trait, the trait must possess heritable variation and must confer an advantage in the competition for resources. If one of these requirements does not occur, then the trait does not experience natural selection. (We now know that such traits may change by other evolutionary mechanisms that have been discovered since Darwin’s time.)
Natural selection operates by comparative advantage, not an absolute standard of design. “…as natural selection acts by competition for resources, it adapts the inhabitants of each country only in relation to the degree of perfection of their associates” (Charles Darwin, On the Origin of Species, 1859).
During the twentieth century, genetics was integrated with Darwin’s mechanism, allowing us to evaluate natural selection as the differential survival and reproduction of genotypes, corresponding to particular phenotypes. Natural selection can only work on existing variation within a population. Such variations arise by mutation, a change in some part of the genetic code for a trait. Mutations arise by chance and without foresight for the potential advantage or disadvantage of the mutation. In other words, variations do not arise because they are needed.
Evidence of Natural Selection
Let's look at an example to help make natural selection clear.
Industrial melanism is a phenomenon that affected over 70 species of moths in England. It has been best studied in the peppered moth, Biston betularia. Prior to 1800, the typical moth of the species had a light pattern (see Figure 2). Dark colored or melanic moths were rare and were therefore collectors' items.
Figure 2. Image of Peppered Moth |
During the Industrial Revolution, soot and other industrial wastes darkened tree trunks and killed off lichens. The light-colored morph of the moth became rare and the dark morph became abundant. In 1819, the first melanic morph was seen; by 1886, it was far more common -- illustrating rapid evolutionary change. 
Eventually light morphs were common in only a few locales, far from industrial areas. The cause of this change was thought to be selective predation by birds, which favored camouflage coloration in the moth.
In the 1950's, the biologist Kettlewell did release-recapture experiments using both morphs. A brief summary of his results are shown below. By observing bird predation from blinds, he could confirm that conspicuousness of moth greatly influenced the chance it would be eaten.
Recapture Success
light moth
|
dark moth
| |
non-industrial woods
|
14.6 %
|
4.7 %
|
industrial woods
|
13 %
|
27.5 %
|
Local Adaptation - More Examples
So far in today's lecture we have emphasized that natural selection is the cornerstone of evolutionary theory. It provides the mechanism for adaptive change. Any change in the environment (such as a change in the background color of the tree trunk that you roost on) is likely to lead to local adaptation. Any widespread population is likely to experience different environmental conditions in different parts of its range. As a consequence it will soon consist of a number of sub-populations that differ slightly, or even considerably.
The following are examples that illustrate the adaptation of populations to local conditions.
- The rat snake, Elaphe obsoleta, has recognizably different populations in different locales of eastern North America (see Figure 3). Whether these should be called geographic "races" or subspecies is debatable. These populations all comprise one species, because mating can occur between adjacent populations, causing the species to share a common gene pool (see thelecture on speciation).
Figure 3: Subspecies of the rat snake Elaphe obsoleta, which interbreed where their ranges meet.
- Galapagos finches are the famous example from Darwin's voyage. Each island of the Galapagos that Darwin visited had its own kind of finch (14 in all), found nowhere else in the world. Some had beaks adapted for eating large seeds, others for small seeds, some had parrot-like beaks for feeding on buds and fruits, and some had slender beaks for feeding on small insects (see Figure 4). One used a thorn to probe for insect larvae in wood, like some woodpeckers do. (Six were ground-dwellers, and eight were tree finches.) (This diversification into different ecological roles, or niches, is thought to be necessary to permit the coexistence of multiple species, a topic we will examined in a later lecture.) To Darwin, it appeared that each was slightly modified from an original colonist, probably the finch on the mainland of South America, some 600 miles to the east. It is probable that adaptive radiation led to the formation of so many species because other birds were few or absent, leaving empty niches to fill; and because the numerous islands of the Galapagos provided ample opportunity for geographic isolation.
Figure 4
Stabilizing, Directional, and Diversifying Selection
Finally, we will look at a statistical way of thinking about selection. Suppose that each population can be portrayed as a frequency distribution for some trait -- beak size, for instance. Note again that variation in a trait is the critical raw material for evolution to occur.
What will the frequency distribution look like in the next generation?
Figures 5a-c |
First, the proportion of individuals with each value of the trait (size of beak, or body weight) might be exactly the same. Second, there may be directional change in just one direction. Third (and with such rarity that its existence is debatable), there might be simultaneous change in both directions (e.g. both larger and smaller beaks are favored, at the expense of those of intermediate size). Figures 5a-c capture these three major categories of natural selection.
Figure 6 |
Under stabilizing selection, extreme varieties from both ends of the frequency distribution are eliminated. The frequency distribution looks exactly as it did in the generation before (see Figure 5a). Probably this is the most common form of natural selection, and we often mistake it for no selection. A real-life example is that of birth weight of human babies (see Figure 6).
Under directional selection, individuals at one end of the distribution of beak sizes do especially well, and so the frequency distribution of the trait in the subsequent generation is shifted from where it was in the parental generation (see Figure 5b). This is what we usually think of as natural selection. Industrial melanism was such an example.
Figure 7 |
The fossil lineage of the horse provides a remarkable demonstration of directional succession. The full lineage is quite complicated and is not just a simple line from the tiny dawn horse Hyracotherium of the early Eocene, to today's familiar Equus. Overall, though, the horse has evolved from a small-bodied ancestor built for moving through woodlands and thickets to its long- legged descendent built for speed on the open grassland. This evolution has involved well- documented changes in teeth, leg length, and toe structure (see Figure 7).
Under diversifying (disruptive) selection, both extremes are favored at the expense of intermediate varieties (see Figure 5c). This is uncommon, but of theoretical interest because it suggests a mechanism for species formation without geographic isolation (see the lecture on speciation).
Summary
Darwin's theory of evolution fundamentally changed the direction of future scientific thought, though it was built on a growing body of thought that began to question prior ideas about the natural world.
The core of Darwin's theory is natural selection, a process that occurs over successive generations and is defined as the differential reproduction of genotypes.
Natural selection requires heritable variation in a given trait, and differential survival and reproduction associated with possession of that trait.
Examples of natural selection are well-documented, both by observation and through the fossil record.
Selection acts on the frequency of traits, and can take the form of stabilizing, directional, or diversifying selection.(http://www.globalchange.umich.edu/globalchange1/current/lectures/selection/selection.html)
Creation
Creation may refer to:
In religion and philosophy
o
Creation
ex nihilo, the concept that
matter comes "from nothing"
o
Creation myth, stories of the supernatural creation of the
Earth
o
Genesis creation narrative, the biblical account of creation
In science and technology
o
Matter creation, the appearance of elementary particles, in
physical processes such as pair production.( http://en.wikipedia.org/wiki/Creation)
5 Interesting Theories on World Creation
For centuries, people have wondered how the world was created. We may never know how we came to be, but there are many different theories on the subject. From scientists to mathematicians to religious deities all have theories on how the world was created. What theory you choose to believe is up to you.
1. The Mayans
According to the Mayans, there were two people, Tepeu and Gucumatz. They would sit around and think about things and then those things would exist. They thought up the mountains, the earth, the oceans, the sky and the animals and once they did they appeared. They used clay to create people, which would fall apart when they got wet, so they made people at of wood. These people would cause trouble so the God created a flood and wiped them out. They were allowed to start over. This is how the Earth became what it is today.
2. The Scandinavians
According the Scandinavians, there was an emptiness that needed to be filled. There were two Gods, Muspell and Niflhiem. Muspell was the leader of the fiery realm and Niflhiem was the leader of the icy realm. They would plat in this vast open space. Inside the space the air grew mild and once the ice started to melt, Ymir was created. He was an evil God. While Ymir slept, he sweated and brought to life two males and a female frost giant. More ice melted in the time passed and a cow was created. She had plenty of milk to feed Ymir. She would nourish herself by licking the ice blocks. After a few days of licking the ice, she revealed a man who had a son. The son married one of the frost giant’s daughters and they had three sons, who killed Ymir. The blood that flowed from Ymir drowned all the frost giants except for Berglimir and his wife. They took the flesh and bones of Ymir and then created the Earth. While walking along the Earth’s surface Odin, one of the sons of the frost giant, spotted two logs and gave them life, while one of the other brothers gave them brains and feelings and the other gave them hearing and sight. From this man and women all life is created.
3. The Chinese
Chinese believe that in the beginning heaven and Earth were as one. The universe was a big black egg that carried a God, Pan-Gu, inside itself. Pan Gu awoke from a 18 thousand year nap and wanted out of the egg. He took his broad axe and smashed through. The light became the heavens and the heavier parts became the Earth. Pan-Gu stood in between with his head touching the heavens and his feet firmly planted on the Earth. All three would grow at a rate of ten feet per day. After 18 thousand years everything stopped growing. After his passing, he breathe became the wind and the clouds. His voice is the thunder and his eyes became the sun and moon. The mountains were formed from his body and limbs and the rivers and oceans are made of his blood. The fertile soil is from his muscles and the roads are his veins. The flowers and trees are from his skin and body hair, where the stars are from his beard and hair. Pearls and jade are made from his marrow and his sweat is the rain and dew.
4. The Australians
In Australia they believe that the earth was plain and bare in the beginning. There was no light, life or death. The sun, moon, stars and eternal ancestors all slept beneath the Earth. When the ancestors arose, they would walk the earth in human form, animal form, plant form or a combination of the forms. There were two people that formed out of nothing and upon their walks across the Earth’s surface they would come upon some half finished plants, animals and humans. They would then carve heads, bodies and limbs from bundles of plants. This is how people were formed amongst the Earth’s surface. After the work of human creation was finished the ancestors went back to sleep. They either went back under the Earth or they stayed here in the form of plants and animals. They left sacred trails, which can be seen in the forms watering holes, rocks and trees.
5. The Apache Indians
They believed that in the beginning there was nothing. Suddenly, there was a thin disk with a man inside. After awaking from his nap he looked up and light appeared, looking down he created a sea of light, to the east he created the streaks of dawn and to the west the colorful streaks of dusk. After creating all the light, he wiped his hands together and then thrust them in a downward motion. A girl on a cloud appeared. He asked her where she was going and she did not answer. She asked him where he was from and he said from the east. She asked where the earth was and he asked where the sky was. He sang four times, which is the lucky number to the Apache Indians that he was thinking of what to create next. He flung his hands wide open and then appeared the sun God. He then dropped his hands and then a small boy appeared. All four Gods where now present and they all shook hands, mixing their sweat together and then he sang about making the Earth again four times. After rubbing his hands together, a brown ball appeared. He kicked it and it expanded, the girl kicked it and it did the same, the sun God and the boy both took turns and the ball continued to expand. He then told the wind to go inside and blow it up. The Creator had created more Gods to look over things on Earth. He had created workers to help with the building of Earth. Once he seen work was done, then he disappeared leaving the works to create the world’s population.
Author: Harmony Stalter — Copyrighted © roadtickle.com(http://roadtickle.com/5-interesting-theories-on-world-creation/)
Creation versus Evolution
We compare the theory of evolution with the
Bible’s creation account in easy-to-understand terms, using
evidence from the fields of paleontology, geology, biology, and astronomy. We
provide links and a bibliography for those who want to study both sides of the
issue. We fully explain all the scientific terms on this page.
Note: This page is long. It may be easier to
read if you print it out on paper. Print one test page first, as some
browser/printer combinations make this text very light.
How did humans (and everything else) come
into existence? The only explanation you will find in public school and
university textbooks is the theory of evolution. Yet, no scientific,
provable evidence supporting the theory of evolution has emerged since Charles
Darwin popularized it in 1859.
If there is no support for the theory of
evolution, why is no alternative taught? We can only think of two reasons:
>The Bible’s creation account is not “politically
acceptable.”
>The authors, book publishers, and school boards do not have all the facts.
>The authors, book publishers, and school boards do not have all the facts.
We
can not help the first condition. This page does contain all the necessary
information needed for everyone else.
Two Views of How We Got Here
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