It took 200,000 years for humans to reach 3 billion in number. It took 40 years for the next 3 billion.
11
When you are looking at someone you love, your pupils dilate, they do the same when you are looking at someone you hate.
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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
Your fingernails grow faster in summer.
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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
In one day, adult lungs move about 10,000 litres of air.
11
The human brain doesn't stop developing until about 25 years old.
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