Biology
Your heart beats over 2.5 billion times in a lifetime
Around 100,000 beats a day, pumping some 7,000 litres of blood, without a single voluntary command from you.
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Your cells carry a second, separate genome
Mitochondria have their own small circular DNA, inherited only from your mother. They are thought to descend from ancient bacteria absorbed by our ancestors' cells.
One cell holds about two metres of DNA
Packed into a nucleus a few micrometres wide, your DNA is wound and coiled with astonishing efficiency. Stretched end to end, the DNA in your whole body would reach far beyond the Sun.
You carry roughly as many bacterial cells as human ones
Current estimates put the ratio near one to one — tens of trillions of microbes, mostly in your gut, helping digest food and train your immune system.
A red blood cell lives about 120 days
It has no nucleus, so it cannot repair itself. In that short life it makes roughly 170,000 trips around your body before being recycled in the spleen.
Your outer skin is completely replaced every month
The epidermis renews itself continuously, and humans shed on the order of tens of thousands of skin cells every minute. Much of household dust is you.
Most of the oxygen you breathe came from the ocean
Marine phytoplankton — microscopic drifting algae — produce roughly half of Earth's oxygen, rivalling every forest on land combined.