The Scientific Evidences of Organic Evolution. By G. J. Romanes,
With the discovery of DNA deoxyribonucleic acid in by Francis Crick and James Watson, the study of evolution entered yet another phase, taking it to its most fundamental level. Crick and Watson found that DNA contains the genetic instructions used in the development and functioning of all known living organisms. Chemically DNA is a long polymer of simple units called nucleotides, with a backbone made of sugars and phosphate atoms joined by ester bonds. Attached to each sugar is one of four types of molecules called bases. It is the sequence of these four bases along the backbone that encodes information, and the main role of DNA is the long-term storage of information.
Within cells, DNA is organized into structures called chromosomes and the set of chromosomes within a cell make up a genome. These chromosomes are duplicated before cells divide, in a process called DNA replication. DNA is the ultimate source of both change and continuity in evolution. The modification of DNA through occasional changes or rearrangement in the base sequences underlies the emergence of new traits, and thus of new species.
At the same time, all organisms use the same molecular codes of the four DNA base sequences. This uniformity in the genetic code is powerful evidence for the interrelatedness of living things, suggesting that all organisms presently alive share a common ancestor that can be traced back to the origins of life on Earth Kennedy et al. Explore This Park.
Geologic Principles—Organic Evolution. Fossil trackway in the Coconino Sandstone about million years old made by Chelichnus, a reptile like mammal. Grand Canyon National Park, Arizona. Eicher provides the following summary: Populations of animals and plants produce progeny at such a rate that were they all to survive, they would increase rapidly year after year.
Spectacular progressive increases in population size do not, in fact, occur. Although most populations fluctuate year by year, they remain essentially constant over the long term. A very real struggle for existence occurs in nature. Each individual must compete for food and must cope successfully with every facet of the environment—both physical, such as climate extremes, and biological, such as diseases and predators—in order to live to produce progeny.
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Each individual differs from virtually all others in its species. Darwin noted that species in nature had similar potential for modification.
Here Darwin made a break with all previous suggestions on the subject. Evolution by natural selection is one of the best substantiated theories in the history of science, supported by evidence from a wide variety of scientific disciplines, including paleontology, geology, genetics and developmental biology.
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More simply put, the theory can be described as "descent with modification," said Briana Pobiner, an anthropologist and educator at the Smithsonian Institution National Museum of Natural History in Washington, D. The theory is sometimes described as " survival of the fittest ," but that can be misleading, Pobiner said. Here, "fitness" refers not to an organism's strength or athletic ability, but rather the ability to survive and reproduce.
For example, a study on human evolution on 1, students, published online in the journal Personality and Individual Differences in October , found that many people may have trouble finding a mate because of rapidly changing social technological advances that are evolving faster than humans.
In the first edition of "On the Origin of Species" in , Charles Darwin speculated about how natural selection could cause a land mammal to turn into a whale.
As a hypothetical example, Darwin used North American black bears, which were known to catch insects by swimming in the water with their mouths open:. The idea didn't go over very well with the public.
Darwin was so embarrassed by the ridicule he received that the swimming-bear passage was removed from later editions of the book. Scientists now know that Darwin had the right idea but the wrong animal.
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Instead of looking at bears, he should have instead been looking at cows and hippopotamuses. The story of the origin of whales is one of evolution's most fascinating tales and one of the best examples scientists have of natural selection. To understand the origin of whales, it's necessary to have a basic understanding of how natural selection works. Natural selection can change a species in small ways, causing a population to change color or size over the course of several generations. This is called "microevolution.click
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But natural selection is also capable of much more. Given enough time and enough accumulated changes, natural selection can create entirely new species, known as "macroevolution. Take the example of whales — using evolution as their guide and knowing how natural selection works, biologists knew that the transition of early whales from land to water occurred in a series of predictable steps.
The evolution of the blowhole, for example, might have happened in the following way:. Random genetic changes resulted in at least one whale having its nostrils placed farther back on its head. Those animals with this adaptation would have been better suited to a marine lifestyle, since they would not have had to completely surface to breathe.
Such animals would have been more successful and had more offspring.
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In later generations, more genetic changes occurred, moving the nose farther back on the head. Other body parts of early whales also changed. Front legs became flippers.
Darwin's Theory of Evolution: Definition & Evidence | Live Science
Back legs disappeared. Their bodies became more streamlined and they developed tail flukes to better propel themselves through water. Darwin also described a form of natural selection that depends on an organism's success at attracting a mate, a process known as sexual selection. The colorful plumage of peacocks and the antlers of male deer are both examples of traits that evolved under this type of selection. But Darwin wasn't the first or only scientist to develop a theory of evolution. The French biologist Jean-Baptiste Lamarck came up with the idea that an organism could pass on traits to its offspring, though he was wrong about some of the details.