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 twice as long to lose new muscle if you stop working out than it did to gain it.
127
The human eye blinks an average of 4,200,000 times a year.
233
Your fingernails grow faster in summer.
744
Early American humans hunted car-size armadillos and used their shells for houses.
12
The average person's skin weighs twice as much as their brain.
131
Your heart will pump about 212 million liters in its lifetime.
26
Blue eyes are a genetic mutation. Before the mutation occured, all humans had brown eyes.
89