Skunks, easily identifiable by their characteristic black and white striping, are infamous for producing a foul odor when frightened. Fortunately, these mild-mannered creatures rarely use this potent defense, and provide quite a few benefits to the areas they inhabit. In cases where eviction is necessary, a few mild harassment and deterrence techniques can help you humanely remove skunks while escaping smell-free.
Register for a free to start saving and receiving special member only perks. Science is a particular way of knowing about the world. In science, explanations are restricted to those that can be inferred from confirmable data—the obtained through observations and experiments that can be substantiated by other scientists. Anything that can be observed or measured is amenable to scientific investigation.
Explanations that cannot be based on empirical evidence are not a part of science. The history of life on earth is a fascinating subject that can be studied through observations made today, and these observations have led to compelling s of how organisms have changed over time. The best available evidence suggests that life on earth began more than three and a half billion years ago.
For more than two billion years after that, life was housed in the bodies of many kinds of tiny, single-celled organisms, some of which produced the oxygen that now makes up more than a fifth of the earth's atmosphere. Less than a billion years ago, much more complex organisms appeared. By about half a billion years ago, evolution had resulted in a wide variety of multicellular animals and plants living in the sea that are the clear ancestors of many of the major types of organisms that continue to live to this day.
Somewhat more than million years ago, some marine plants and animals began one of the greatest of all innovations in evolution—they invaded dry land. For our own phylum, the Chordata, this move away from the nurturing sea led to the appearance of amphibians, reptiles, birds, and mammals—the latter including, of course, our own species, Homo sapiens. This chapter looks at how science works in the context of our overall understanding of how biological evolution occurred. It begins, however, by discussing another scientific development that challenged long-held understandings and beliefs: Trying again seeking a wild one discovery of heliocentricism.
Surely one of the first major natural phenomena to be understood was the cause of night and day. Some of the earliest surviving human records left on clay tablets relate to the movements of the sun and other celestial bodies. The obvious cause of day and night is the rising and setting of the sun.
This is an observation that can be made today by anyone and, seemingly, requires no further explanation. Archaeological evidence and early records make it clear that our ancestors realized that not only does the sun appear to rise and set, but so do the moon and stars.
The movements of the moon and stars, however, are not precisely synchronized with. Clockwise from top left, Nicolaus CopernicusJohannes KeplerGalileo Galileiand Isaac Newton led the way to a new understanding of the relationship between the earth and the sun and initiated an age of scientific progress that continues today. Illustration from the 18th century depicts the Ptolemaic system in the upper left corner and the Copernican system in other corners and center. The moon is slower by about one hour per day.
The stars remain almost the same on successive nights, but slowly it becomes obvious that they, too, are slowed in their movements compared to the sun. Thus, the stars of summer are different from those visible in the winter. In fact, it takes a full year for the stars to return to their position, an interval of time that defines our year.
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The ancient observers realized that not all stars move in unison. Although most move in majestic unity, a few others are "wanderers"—appearing now with one group of stars and a week later somewhere else. The majority were called "fixed stars," the wanderers were called "planets. During the late Middle Ages, and especially in the Renaissance, beautiful brass models known as orreries were made to show the relative positions and movements of the sun, planets, and moon as they circled the earth.
As the center of the universe, the earth was a sphere in the center of the orrery. The other celestial bodies were positioned on rings of metal, each moving by clockwork at its own rate. The fixed stars required a simple solution—they could be considered stuck in an outermost shell, also moved by clockwork.
The problem with orreries—and with the theories of the cosmos then prevailing—was that they had to become successively more complex as more became known. Careful observations of the movements of the stars and planets greatly complicated the hypotheses used to for those movements.
This growing complexity stimulated some of the leading astronomers of the 16th and 17th centuries, including Copernicus, Kepler, and Galileo, to make even more precise observations of the movements of the heavenly bodies. Astronomers used these measurements to demonstrate that the age-old human explanations of the heavens were incomplete.
In the process, they replaced a complex and confusing explanation with a simple one: the sun, rather than the earth, is at the center of a "solar system," and the earth revolves around it.
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That simple step—a bold departure from past thinking due mainly to the insights of Copernicus to —dramatically changed the picture of the then known universe. This concept of heliocentricism initially ran counter to the positions of religious authorities. The view of Christianity over most of its history, based on a literal interpretation of the Bible, was that the earth is the center of the universe around which the celestial bodies revolve.
Copernicus dedicated his book describing the theory of heliocentricism, De revolutionibus orbium coelestiumto Pope Paul III and promptly died. That saved him the troubles that were to beset Galileo towhose astronomical observations confirmed the views of Copernicus.
Galileo was told to abandon his beliefs, and he later was tried by the Inquisition and sentenced to the equivalent of house arrest. The Church held that his views were dangerous to faith. Continued study and ever more careful measurements of the movements of the planets and sun continued to support the heliocentric hypothesis.
Then, in the latter half of the 17th century, Isaac Newton to showed that the force of gravity—as measured on the earth—could for the movements of the planets given the laws of motion that Newton derived.
As a result of the steady accumulation of evidence, the theological interpretation of celestial movements gave way to the naturalistic explanation, and it is now accepted that night and day are the consequences of the rotation of the earth on its axis.
Today, we can see for ourselves the rotation of the earth from satellites orbiting the planet. Like biological evolution, the theory of heliocentricism brought order and new understanding to an otherwise chaotic and confusing aspect of nature.
It also had great practical applications, in that the exploration of the world by European seafarers used the more accurate understanding of celestial mechanics to assist in. Looking at the night sky remains a powerful experience.
But that experience is now informed not only by the beauty and majesty of the heavens, but by a deeper understanding of nature and by an appreciation of the power of the human intellect. This triumph of the human mind says a great deal about the nature of science.
First, science is not the same as common sense. Common sense indicates that the sun does rise and set. Nevertheless, there can be other explanations of that phenomenon, and one of them, the rotation of the earth on its axis, is responsible for day and night. A concept based on observation proved to need extensive modification as new observations accumulated. Second, the statements of science should never be accepted as "final truth. Nevertheless, in the case of heliocentricism as in evolution, the data are so convincing that the accuracy of the theory is no Trying again seeking a wild one questioned in science.
Third, scientific progress depends on individuals, but the contributions of one individual could be made by others. If Copernicus had kept his ideas to himself, the discovery of heliocentricism would have been postponed, but it would not have been blocked, since other astronomers eventually would have come to the same conclusion. Biologists have used construction cranes to study the many newly discovered species that live in the canopies of tropical forests, as in this research project in Panama.
Similarly, had Darwin and Wallace not published their hypotheses, the concept of biological evolution would nevertheless have emerged as the accepted explanation for the history of life on earth. The same cannot be said in other areas of human endeavor; for example, had Shakespeare never published, we would most assuredly never have had his plays.
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The publications of scientists, unlike those of playwrights, are a means to an end—they are not the end itself. What are the scientific methods that have led to our current understanding of the history of life over vast eons of time? They begin with careful descriptions of the material being studied.
The material for the study of biological evolution is life itself. One basic aspect of life is that individuals can be grouped as similar kinds, or species.
Another important observation is that many species seem to be closely related to each other. The scientific classification of species and their arrangement into groups began with the publication in of Systema Naturaeor system of nature, by the Swedish naturalist Carolus Linnaeus to For example, Linnaeus knew seven dog-like species, and he gave each a double name. Subsequently many more species were discovered and some of the names were changed—and continue to be changed as more information is obtained.
The domestic dog is Canis familiaris ; the coyote of North America is Canis latrans ; the Australian dingo is Canis dingo ; and the wolf of the northern hemisphere is Canis lupus. Thus Canis is the name of the genus of dog-like animals, and the distinctive second name is the species name. Whereas Linnaeus recognized about 9, species, systematists now have recognized about 1.
The task of categorizing and describing species is still far from complete. Most species of smaller invertebrates, and many bacteria and other microscopic organisms, remain to be discovered.