A Boy for Every Girl? Not Even Close

Gregory Hurst, a coauthor of the Current Biology study, is a University of Liverpool professor of evolutionary biology.

Hurst told me, "Sex ratio variation is quite common in invertebrates, slightly less so in vertebrates."

In the above circumstance, a parasite targets males, killing them off and leading to the ratio discrepancy.

So how do we human vertebrates rate in nature's sex match game? I'd give us a B-.

Did you know that about 107 males are born for every 100 females? No one is quite certain why and, sadly, the data could be due to intentional under-reporting of female births, but that's the documented ratio.

Here's some more human sex ratio trivia, as reported by About.com's Matt Rosenberg on About's Geography site :

"The countries that have the highest proportion of human males to females are...

Armenia – 115:100
Azerbaijan – 114:100
Georgia – 113:100
India – 112:100
China – 111:100
Albania – 110:100

(A one to one match; Credit: ainlondon)

The United Kingdom and United States have a sex ratio of 105:100 while Canada has a sex ratio of 106:100. (The U.S. stats must pull from the 14-to-24 years of age group.)

The countries with the lowest proportion of males to females are...

Grenada and Liechtenstein – 100:100
Malawi and Barbados – 101:100"

And, finally, here is data from the U.S. Census Bureau. The footnotes refer to adjusted or estimated numbers.

Study the chart carefully, as it includes some surprising information. For example, note the differences in the 65 years and over columns across the years. There was a peak in 1950, a gradual decline, and now an upswing. Why?

Ratio of Males to Females by Age Group (1950-2005)

(Number of males per 100 females, total resident population)