It took 200,000 years for humans to reach 3 billion in number. It took 40 years for the next 3 billion.
11
By weight, Bone is five times stronger than steel.
417
Yawns are more contagious among people with closer relationships.
163
Gorillas can catch human colds and other illnesses.
205
Our eyes are always the same size from birth, but our nose and ears never stop growing.
266
Enamel is hardest substance in the human body.
61
An average heart beats 100,000 times a day, pumping some 2,000 gallons of blood through its chambers. Over a 70-year life span, that adds up to more than 2.5 billion heartbeats.
73
The adult human brain weighs about 3 pounds (1,300-1,400 g).
99