According to [this Wikipedia page][1], there is already an imbalance in sex ratio towards males (1.1:1.0). So I'm not sure the even distribution is practical towards sex ratio, at least in *Homo sapien*.

You want to know if this imbalance is taken to the extreme.

> Mating/relationships

This can go one of two ways.

(A) If modern *Homo sapien* continues a focus on evolutionary advantage, males will be highly possessive of females. They will become hyper aggressive towards males who enter their territory, becoming more likely to attack if they feel their claim over a female is threatened or disputed. Females will largely become trophies, rarely leaving the male's side while in the public space. Males will certainly feel they deserve sexual intercourse with their female and the female has no right to deny him.

(B) If modern *Homo sapien* deviates from evolutionary necessity, females will be communal property. Males may not lay claim to a female for more than a night. Females will be expected to mate with as many different males as possible, to ensure diversity in the species. As a result of this artificial construct, females will control the relationship and males will take on an eye candy role. Males will have to prove they are better than other members of the species, much in the same way that animals display plumage or perform exotic dances to impress.
   

> Social structure

If situation (A) manifests, society is going to be comprised of closed-door communities where males are dominant players. Females will be secluded from society, not permitted to wander on their own. Males won't even trust their female(s) to guards, since the guards are either male and have reason to break faith or they're female and are at the same risk as their charge. Males will flaunt their female(s) when they can, with more appealing individuals appearing with the male at every opportunity. Males may never leave home without their most appealing female under their arm. Males, of course, will be suspicious of each other, so there will be far fewer grand celebrations or gatherings at local bars. Sports will take on new connotations, perhaps where females are part of the reward. Females will certainly become a teaser for males to use to keep other males in their influence: "If you do this for me, I'll let you sleep with Amelia for a week."

If situation (B) arises, females will more often hold positions of power. Sex will be given out as special favors and rewards. Females will be free to choose who advances on their merits, rewarding loyalty and intelligence with less emphasis on who knows who. This kind of society will be far more stable, as males will try to keep females in a good mood to raise their own chance to have sexual intercourse and pass on their genes. There won't be much upheaval, as the minority will control the majority of power and influence. Males will still have the greater ability to flaunt their sexual endeavors. Females would be expected and almost required to have sex with as many males as they could, but males have limited opportunity. When a male manages to have sexual intercourse with a female, he can flaunt that reward/privilege.

> Gender roles

In both cases I've outlined above, females are still the "eye candy," so I'll explore a few other areas of general society.

In society (A), males run the government exclusively. They're in charge of stores, organizations, and companies. There will be few females in any field that involves entering the public domain. They are unlikely to obtain a higher education prior to the development of the Internet. Their efforts will be dedicated to home-bound activities, such as knitting, painting, and animal husbandry.

In society (B), females will hold a majority of influence in government, even when they don't hold a majority of seats. Females will be given priority in higher education, possibly leading to higher numbers of females in the science, technology, engineering, and math (STEM) fields; these fields are currently dominated by males because males are statistically better at spacial and analytical skills.

  [1]: http://en.wikipedia.org/wiki/List_of_countries_by_sex_ratio