Answer:
The disease has been absent from the population for a long time.
Formation of the Earth's Atmosphere. The early Earth was very different from our Earth today. The early Earth experienced frequent impacts from asteroids and meteorites and had much more frequent volcanic eruptions. There was no life on Earth for the first billion years because the atmosphere was not suitable for life.
1.), missing links
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The insulin receptors have specific shape that is compatible to the glucose molecules. The glucose molecules bind to these receptors, which tells the pancreas to release insulin in order to lower the blood glucose level. Any kind of change in the shape of these receptors because of mutation will hinder this cell communication and stop the insulin release. This will lead to high levels of blood sugar level.