It took 200,000 years for humans to reach 3 billion in number. It took 40 years for the next 3 billion.
11
Enamel is hardest substance in the human body.
61
An unprotected human can survive up to 1.5 minutes in space with no permanent bodily damage.
82
Every human spent about half an hour as a single cell.
144
Only 12,000 years ago there was a species closely related to modern humans called Homo floresiensis that had been living on an Indonesian Island. They used fire and rather advanced tools, yet were only about 3 feet tall and weighed around 25kg.
15
Coughing can cause air to move through your windpipe faster than the speed of sound - over a thousand feet per second!
197
Tigers can see 6 times better at night than humans.
305
The adult human brain weighs about 3 pounds (1,300-1,400 g).
99