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The Basics of Evolution
- What is evolution?
- What is natural selection?
- How has our understanding of evolution changed since Darwin’s day?
- How long does evolution take?
- Can evolution really be responsible for such amazingly complex biological features, such as the human eye?
 What is evolution?
In a general sense, evolution means “change through time.” This concept has been broadly applied not only to biology, but also in the fields of geology, astronomy, economics and history.
Biological evolution as understood today refers to cumulative changes in gene frequency that occur within populations through time. Over time, inherited genetic changes in populations can produce entirely new species. The central idea of biological evolution is that all life on Earth shares a common ancestor.
The modern understanding of biological evolution begins with the publication of Charles Darwin’s book On the Origin of Species (1859). Darwin himself offered one of the best definitions of evolution, simply stated as “descent with modification.” Because of this book, Darwin stands at the center of one of the great intellectual revolutions in human history.
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- What is natural selection?
Darwin believed that natural selection was the main mechanism that passed favorable variations from generation to generation. Commonly known as “survival of the fittest,” natural selection refers specifically to an organism’s ability to survive and reproduce.
Darwin’s theory of evolution by means of natural selection has four basic tenets:
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Variation exists among individuals within a species;
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Organisms produce more offspring than the environment can support;
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Competition exists between individuals; and, |
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Those individuals who best fit their environment are likely to survive, reproduce, and pass their traits to the next generation.
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Darwin wrestled with the nature of inheritance—exactly how organisms pass traits on to their offspring—until his death in 1882, well before the science of genetics was established. By the mid-twentieth century, advances in the field of genetics, including the discovery of chromosomes, genes, and the DNA double helix, had revealed the importance of genetic variation to evolution.
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- How has our understanding of evolution changed since Darwin’s day?
Since the publication of Darwin’s On the Origin of Species, evolutionary science has matured dramatically. Darwin published his theory without any knowledge of genetics, fully aware that he could not explain exactly how traits were inherited and passed from generation to generation.
But research in genetics and molecular biology has now revealed how traits are inherited from parent to offspring.
Joining forces with paleontologists and biologists, geneticists ushered in a new era of interdisciplinary evolutionary research early in the twentieth century. New discoveries in genetics, developmental biology, population biology, and comparative anatomy yielded powerful evidence in support of evolution. This great merging of ideas and approaches is called the “Modern Synthesis” in evolutionary theory.
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 How long does evolution take?
Evolution takes place on different time scales. Scientists refer to evolutionary changes over short time scales, such as one generation, as microevolution. These changes take place within a population or group of interbreeding organisms. Examples of microevolution include insects that become resistant to pesticides, bacterial strains that evolve resistance to antibiotics, and trends in bird body sizes across regions.
In contrast, macroevolution operates over much longer time scales and involves major evolutionary transformations that result in the appearance of new evolutionary lineages. Examples of macroevolution include the evolution of amphibians from fishes. Macroevolution is the cumulative effect of microevolution. Another way to express the difference is that macroevolution is between-species evolution and microevolution is within-species evolution.
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- Can evolution really be responsible for amazingly complex biological features, such as the human eye?
Yes. Evolution can produce extremely complex structures. Darwin reasoned that “if numerous gradations from a simple and imperfect eye to one complex and perfect can be shown to exist” then he felt complex structures like the eye could evolve.
It is thought that a simple light-sensitive spot on the skin of an ancestral animal conferred a slight evolutionary advantage to escape predators or find food. These successful organisms were favored to survive and passed their genes to the next generation. Over millions of years, accumulated random genetic changes and natural selection eventually produced a complex eye.
Because complex eyes have developed separately in a number of different animal groups, some have claimed that this cannot easily be explained by natural selection. One dramatic recent finding in molecular genetics is that there is a common set of genes involved in the early development of anatomically complex eyes of all animals, thus providing a basis for natural selection in independent lineages.
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Continue to Intelligent Design and Evolution. >>
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