It took 200,000 years for humans to reach 3 billion in number. It took 40 years for the next 3 billion.
11
It takes about 20 seconds for a red blood cell to circle the whole body.
102
You can't tickle yourself.
29
Only humans shed emotional tears.
331
On average, a human being will have sex more than 3,000 times and spend two weeks kissing in their lifetime.
161
Pet dogs and elephants are the only animals that seem to instinctively understand human gesture.
14
The average person's skin weighs twice as much as their brain.
131
On average a woman has 4 sexual partners in her lifetime.
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