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The senior population grows every year. Seniors older than 65 years of age now comprise more than 13% of the total population. However, women outlive men. In the 85-and-over age group, there are only 45 men to every 100 women.
Although the Roman numeral for the number 4 has always been taught to have been "IV," according to historians, the ancient Romans probably used "IIII" most of the time. This is partially backed up by the fact that early grandfather clocks displayed IIII for the number 4 instead of IV. Early clockmakers apparently thought that the IIII balanced out the VIII (used for the number 8) on the clock face and that it just looked better.
There are over 65,000 known species of protozoa. About 10,000 species are parasitic.
There are more sensory neurons in the tongue than in any other part of the body.
The heart is located in the center of the chest, with part of it tipped slightly so that it taps against the left side of the chest.