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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.
Most childhood vaccines are 90–99% effective in preventing disease. Side effects are rarely serious.
The immune system needs 9.5 hours of sleep in total darkness to recharge completely.
Vaccines cause herd immunity. If the majority of people in a community have been vaccinated against a disease, an unvaccinated person is less likely to get the disease since others are less likely to become sick from it and spread the disease.
Over time, chronic hepatitis B virus and hepatitis C virus infections can progress to advanced liver disease, liver failure, and hepatocellular carcinoma. Unlike other forms, more than 80% of hepatitis C infections become chronic and lead to liver disease. When combined with hepatitis B, hepatitis C now accounts for 75% percent of all cases of liver disease around the world. Liver failure caused by hepatitis C is now leading cause of liver transplants in the United States.
![H. erectus migrated out of Africa beginning about 1.8 million years ago and is first known from Geor](https://biology-forums.com/gallery/47/medium_275510_22_02_15_5_56_58_207731480.jpeg)
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