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There are more nerve cells in one human brain than there are stars in the Milky Way.
Looking at the sun may not only cause headache and distort your vision temporarily, but it can also cause permanent eye damage. Any exposure to sunlight adds to the cumulative effects of ultraviolet (UV) radiation on your eyes. UV exposure has been linked to eye disorders such as macular degeneration, solar retinitis, and corneal dystrophies.
Although puberty usually occurs in the early teenage years, the world's youngest parents were two Chinese children who had their first baby when they were 8 and 9 years of age.
In most cases, kidneys can recover from almost complete loss of function, such as in acute kidney (renal) failure.
Cancer has been around as long as humankind, but only in the second half of the twentieth century did the number of cancer cases explode.