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Bacteria have flourished on the earth for over three billion years. They were the first life forms on the planet.
Cancer has been around as long as humankind, but only in the second half of the twentieth century did the number of cancer cases explode.
A strange skin disease referred to as Morgellons has occurred in the southern United States and in California. Symptoms include slowly healing sores, joint pain, persistent fatigue, and a sensation of things crawling through the skin. Another symptom is strange-looking, threadlike extrusions coming out of the skin.
Most childhood vaccines are 90–99% effective in preventing disease. Side effects are rarely serious.
Parkinson's disease is both chronic and progressive. This means that it persists over a long period of time and that its symptoms grow worse over time.