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Egg cells are about the size of a grain of sand. They are formed inside of a female's ovaries before she is even born.
The average human gut is home to perhaps 500 to 1,000 different species of bacteria.
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.
There can actually be a 25-hour time difference between certain locations in the world. The International Date Line passes between the islands of Samoa and American Samoa. It is not a straight line, but "zig-zags" around various island chains. Therefore, Samoa and nearby islands have one date, while American Samoa and nearby islands are one day behind. Daylight saving time is used in some islands, but not in others—further shifting the hours out of sync with natural time.
The first-known contraceptive was crocodile dung, used in Egypt in 2000 BC. Condoms were also reportedly used, made of animal bladders or intestines.