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Bacteria have flourished on the earth for over three billion years. They were the first life forms on the planet.
The liver is the only organ that has the ability to regenerate itself after certain types of damage. As much as 25% of the liver can be removed, and it will still regenerate back to its original shape and size. However, the liver cannot regenerate after severe damage caused by alcohol.
People with high total cholesterol have about two times the risk for heart disease as people with ideal levels.
After a vasectomy, it takes about 12 ejaculations to clear out sperm that were already beyond the blocked area.
Human neurons are so small that they require a microscope in order to be seen. However, some neurons can be up to 3 feet long, such as those that extend from the spinal cord to the toes.