This post is going to be devoted in the subject of population ecology. What is population ecology then? It examines the dynamics of population change and the factors that affect the distribution and abundance of members of a population. In a few words, this particular field helps us understand why populations of some species decline while others increase. All populations have some factors that determine their future such as their size,density,distribution age structure as well as birth and death rates and of course sex ratio.
The last topic, sex ratio, is the one that this post will refer specifically to , and the original question to be answered is ” What is the sex ratio in the United States of America? “
To begin with,what do we call sex ratio?
Man vs Woman 
Sex ratio is the proportion of males and females and it can influence whether the population will increase or decrease in size over time. A balanced sex ratio maximizes population growth while an unbalanced one leaves individuals of one sex without mates.
When it comes to human beings.
Sex ratio at birth has recently emerged as an indicator of certain kinds of sex discrimination in some countries. For instance, high sex ratios at birth in some Asian countries are now attributed to sex-selective abortion and infanticide due to a strong preference for sons. This will affect future marriage patterns and fertility patterns. Eventually, it could cause unrest among young adult males who are unable to find partners.
According to the Census research sex ratio is defined as the number of males per 100 females. A sex ratio of exactly 100 would indicate an equal number of males and females, with a sex ratio under 100 indicating a greater number of females. 
Have you ever wondered what is the sex ratio of Americans?
Sex ratio 
The sex ratio at birth in the United States has been around 105 males for every 100 females, however, since mortality at every age is generally higher for males, the sex ratio naturally declines with age. This tendency progresses through ages 85 and above where there are considerably more surviving women. These trends result in more males at younger ages and more females at older ages. Sex ratios can vary from these patterns for many reasons such as the impact of international or domestic migration on a population or features of the geographic location (for example, the existence of college student housing or military facilities).
According to the 2010 Census, the population of the United States on April 1, 2010, was 308.7 million people, representing a 9.7 percent increase in population since 2000, when the population was 281.4 million.
More specifically :157.0 million were female (50.8 percent) while 151.8 million were male (49.2 percent). Between 2000 and 2010, the male population grew at a slightly faster rate (9.9 percent) than the female population (9.5 percent).
Sex ratios were higher in Western states and lower in Northeastern states and compared to 2000, there were fewer counties in 2010 where the female population outnumbered the male population.
Notice that! : There were approximately twice as many women as men at age 89 (361,309 compared with 176,689, respectively). This point occurs about 4 years older than it did in 2000, and 6 years older than it did in 1990. This increase is further evidence of the narrowing gap in mortality between men and women occurring at the older ages.
Where are all the men? 
And if you have been wondering what is the world’s sex ratio,here is your answer.
|World||at birth: 1.07 male(s)/female
under 15 years: 1.07 male(s)/female
15-64 years: 1.02 male(s)/female
65 years and over: 0.79 male(s)/female
total population: 1.01 male(s)/female (2011 est.)
World Sex Ratio 
It is very interesting to know about the sex ratio when it comes to human beings and researches such as this of Census can help researchers studying trends related to mortality and population aging. Overall, the USA population ratio is balanced, predisposing a population increase. Have you ever wondered about your country’s sex rate? If so, you can satisfy your curiosity on CIA’s official site, by clicking on this link :
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 Withgott, Jay, Barbara W. Murck, and Scott R. Brennan. Environment: The Science Behind the Stories. Toronto: Pearson Canada, 2009. Print.