SEX RATIO
Sex ratio is the ratio of males to females in a population. The primary sex ratio is the ratio at the time of conception; secondary sex ratio is the ratio at time of birth; and tertiary sex ratio is the ratio of mature organisms.
In humans, the secondary sex ratio – sex at the time of birth – is commonly assumed to be 105. That is, 105 boys are born for every 100 girls. While this varies by country, it means 51% of babies born worldwide are boys and 49% are girls.
The secondary sex ratio in the United States, where more than 4 million babies are born each year, is consistent with the worldwide sex ratio of 105.
In 2008, approximately 2.16 million boys (51%) were born in the U.S. versus 2.08 million girls (49%). That’s nearly 85,000 more boys.
The tertiary sex ratio (adults) in the U.S. is about 103. So there are more male adults than female adults. There continue to be more males than females until about age 40. Somewhere between the ages of 40 and 64, males start dying off more quickly than females. By age 65, there are only 75 males for every 100 females. That represents a loss of more than one-fourth (28%) of the male population for any given birth year (males who die before the age of 65). For 2008, that would mean approximately 605,000 of the 2.16 million males born will die before the age of 65.
SEX RATIO BY AGE
| Age |
U.S.
Sex Ratio |
World
Sex Ratio |
| At Birth |
105 |
107 |
| Under 15 years old |
104 |
107 |
| 15 to 64 years old |
100 |
102 |
| 65 years and older |
75 |
79 |
| All Ages |
97 |
101 |
Source: CIA World FactBook
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Last Updated on Tuesday, 04 January 2011 19:30 |