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Evolution Outline

• Geographic distribution of living things
• Homologous structures of organisms
• Similarities in early development
• Darwin proposed that Earth was millions of years old, not thousands.
• During those millions of years, many different forms of species appeared, lived for a time, and then vanished leaving behind remains, or fossils.
• One can examine fossils and view the changes of each one; observe the changes in offspring.
• Each species is slightly different on Island A. Far away, on Island B, the species were also slightly different.
• The species had changed over time as the populations in different places adapted to local environments.
• The species had descended with modifications from a mainland ancestor – when Island A and Island B were combined as a contiguous land mass.
• Different species exist on Island C and Island D. Similar structure and behavior were found in different animals which roamed similar environments.
• As a result, one can conclude that the species now living on different islands had descended from different ancestors.
• Some species, however, are similar because they were living under similar ecological conditions and thus exposed to similar pressures of natural selection.
– Different animals ended up evolving certain striking features in common.
• Look at mammals, reptiles, and birds; each of those creatures has backbones. There are striking similarities, like limbs.
– Some limbs are arms, some are legs; they can also be wings, or even flippers. Each limb has a different form and function, but all are composed of the same basic bones.
• Each limb had adapted in ways so the organism can survive in different conditions.
• Despite the different functions, limb bones all developed from the same clumps of cells in growing embryos; these are called homologous structures.
– Homologous structures prov…

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