It took 200,000 years for humans to reach 3 billion in number. It took 40 years for the next 3 billion.
11
The average sperm cell swims at 8 inches per hour.
4
It takes twice as long to lose new muscle if you stop working out than it did to gain it.
127
Yawns are more contagious among people with closer relationships.
163
The human eye blinks an average of 4,200,000 times a year.
233
Stress can result in more headaches as a result of the body rerouting blood flow to other parts of the body.
92
If Earth's life was compressed into 1 year, then humans would have been around for only 2 seconds.
15