Illustration from showing three women reading the three successive volumes of a novel, possibly borrowed from a circulating library. Defining the book itself is a risky operation. I prefer to be inclusive rather than exclusive, and so I offer a very loose definition. The book, for example, does not simply exist as a bound text of sheets of printed paper -- the traditional codex with which we are most familiar today.
Such a definition forgets two millennia of books before print, and the various forms that textual communication took before the codex was invented. A traditional definition based only on the codex would also exclude hypertext and the virtual book, which have done away with the book's conventional material support.
I prefer to embrace all these forms, from cuneiform script to the printed codex to the digitized electronic book, and to trace the history of the book as far back as the invention of writing systems themselves. The term 'book,' then, is a kind of shorthand that stands for many forms of written textual communication adopted in past societies, using a wide variety of materials.
From the first papyrus scrolls to the painstakingly made illuminated manuscripts of the Middle Ages to today's ebooks and the iPad, Lyons distills the history and evolution of books in the context of a parallel cultural evolution and, as in the case of Gutenberg's printing press, revolution. Amman woodcuts showing a compositor with his composing stick and two-page forme, and printers and bookbinders at work. Navigating through 2, gloriously illustrated years of literary milestones, genres, and groundswells, from serial and dime novels to paperbacks to manga, Lyons ends with a bittersweet contemplation of the fate of the book and the bibliophile after the turn of the digital century.
Similarities in DNA are used to determine the relationships between species in much the same manner as they are used to show relationships between individuals. Comparisons of DNA indicate that humans and chimpanzees are more closely related to each other than either species is to gorillas. The field of molecular systematics focuses on measuring the similarities in these molecules and using this information to work out how different types of organisms are related through evolution. These comparisons have allowed biologists to build a relationship tree of the evolution of life on Earth.
Artificial selection is the controlled breeding of domestic plants and animals. Humans determine which animal or plant will reproduce and which of the offspring will survive; thus, they determine which genes will be passed on to future generations. The process of artificial selection has had a significant impact on the evolution of domestic animals. For example, people have produced different types of dogs by controlled breeding.
The differences in size between the Chihuahua and the Great Dane are the result of artificial selection. Artificial selection has produced a wide variety of plants. In artificial selection the new breed or variety that emerges is the one with random mutations attractive to humans, while in natural selection the surviving species is the one with random mutations useful to it in its non-human environment.
In both natural and artificial selection the variations are a result of random mutations, and the underlying genetic processes are essentially the same.
A (r)evolution in chemistry
Darwin proposed that if humans could achieve dramatic changes in domestic animals in short periods, then natural selection, given millions of years, could produce the differences seen in living things today. Coevolution is a process in which two or more species influence the evolution of each other. All organisms are influenced by life around them; however, in coevolution there is evidence that genetically determined traits in each species directly resulted from the interaction between the two organisms.
An extensively documented case of coevolution is the relationship between Pseudomyrmex , a type of ant , and the acacia , a plant that the ant uses for food and shelter. The relationship between the two is so intimate that it has led to the evolution of special structures and behaviours in both organisms. The ant defends the acacia against herbivores and clears the forest floor of the seeds from competing plants. In response, the plant has evolved swollen thorns that the ants use as shelter and special flower parts that the ants eat. Rather, across a population small genetic changes in both ant and tree benefited each.
The benefit gave a slightly higher chance of the characteristic being passed on to the next generation. Over time, successive mutations created the relationship we observe today.
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Given the right circumstances, and enough time, evolution leads to the emergence of new species. Scientists have struggled to find a precise and all-inclusive definition of species. Ernst Mayr defined a species as a population or group of populations whose members have the potential to interbreed naturally with one another to produce viable, fertile offspring. The members of a species cannot produce viable, fertile offspring with members of other species. Speciation is the lineage-splitting event that results in two separate species forming from a single common ancestral population.
Allopatric speciation begins when a population becomes geographically separated. For speciation to occur, separation must be substantial, so that genetic exchange between the two populations is completely disrupted.
In their separate environments, the genetically isolated groups follow their own unique evolutionary pathways. Each group will accumulate different mutations as well as be subjected to different selective pressures. The accumulated genetic changes may result in separated populations that can no longer interbreed if they are reunited. If interbreeding is no longer possible, then they will be considered different species. Usually the process of speciation is slow, occurring over very long time spans; thus direct observations within human life-spans are rare.
However speciation has been observed in present-day organisms, and past speciation events are recorded in fossils. These fish have complex mating rituals and a variety of colorations; the slight modifications introduced in the new species have changed the mate selection process and the five forms that arose could not be convinced to interbreed.
The theory of evolution is widely accepted among the scientific community, serving to link the diverse speciality areas of biology. The significance of evolutionary theory is summarised by Theodosius Dobzhansky as " nothing in biology makes sense except in the light of evolution.
There is much discussion within the scientific community concerning the mechanisms behind the evolutionary process. For example, the rate at which evolution occurs is still under discussion. In addition, there are conflicting opinions as to which is the primary unit of evolutionary change—the organism or the gene. Darwin and his contemporaries viewed evolution as a slow and gradual process. Evolutionary trees are based on the idea that profound differences in species are the result of many small changes that accumulate over long periods.
Gradualism had its basis in the works of the geologists James Hutton and Charles Lyell. Hutton's view suggests that profound geological change was the cumulative product of a relatively slow continuing operation of processes which can still be seen in operation today, as opposed to catastrophism which promoted the idea that sudden changes had causes which can no longer be seen at work.
A uniformitarian perspective was adopted for biological changes. Such a view can seem to contradict the fossil record, which often shows evidence of new species appearing suddenly, then persisting in that form for long periods.
In the s palaeontologists Niles Eldredge and Stephen Jay Gould developed a theoretical model that suggests that evolution, although a slow process in human terms, undergoes periods of relatively rapid change ranging between 50, and , years  alternating with long periods of relative stability. Their theory is called punctuated equilibrium and explains the fossil record without contradicting Darwin's ideas.
A common unit of selection in evolution is the organism. Natural selection occurs when the reproductive success of an individual is improved or reduced by an inherited characteristic, and reproductive success is measured by the number of an individual's surviving offspring. The organism view has been challenged by a variety of biologists as well as philosophers. Richard Dawkins proposes that much insight can be gained if we look at evolution from the gene's point of view; that is, that natural selection operates as an evolutionary mechanism on genes as well as organisms.
Others view selection working on many levels, not just at a single level of organism or gene; for example, Stephen Jay Gould called for a hierarchical perspective on selection. From Wikipedia, the free encyclopedia. A non-technical explanation of the basic concepts and principles of biological evolution. This article is a non-technical introduction to the subject. For the main encyclopedia article, see Evolution. Darwin's finches by John Gould.
Key topics. Introduction to evolution Evidence of evolution Common descent Evidence of common descent. Processes and outcomes.
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