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Charles Darwin: The Theory of Evolution
Evolution is biology’s chief unifying process; it is the “complex of processes by which living organisms originated on Earth and have been diversified and modified through sustained changes in form and function” (History.com). Charles Darwin, an English naturalist, proposed the theory of evolution and natural selection. On the Origin of Species by Means of Natural Selection, Darwin’s most famous book, has become a milestone in human understanding of nature. With the observation that offspring resemble their parents and are not identical to them, Charles Darwin points out the variability in species.
About 3.4 billion years ago, life originated even when the atmosphere lacked sufficient amounts of free oxygen. The earliest organisms were cells, similar to modern bacteria. These single celled forms (prokaryotes) were at first anaerobic but then diversified into an array of adaptive types from which cyanobacteria descended. Highly developed cells (eukaryotes) could have evolved through the union of a number of distinct unicellular types. “Other features of advanced cells, such as their large DNA contents, may also have arisen from prokaryotic symbionts. Single-celled eukaryotes then developed complex modes of living and advanced types of reproduction that led to the appearance of multicellular plants and animals” (History.com).
The mammals survived a wave of extinction about 65 million years ago that eliminated the dinosaurs. Humans belong to an order of mammals, the primates. Many of the primate characteristics—the overlapping visual fields, short face, large brains, grasping hands, and alertness and curiosity—must have been obtained as arboreal adaptations.
Evolutionary patterns undergo lineages that may evolve slowly at one point in time and rapidly in others; they may diversify hastily at one time and then shrink due to the widespread of extinction. The key to these patterns are the rate and nature of environmental...