why men are more aggressive and not constrained at selective sex where as women are very selective

I guess the reason might be that a born child will have more gene contribution from its father then mother.
  So fathers might be more interested in spreading their own copies in large and  not cared about severe selection of female candidate. Where as women are very selective in choosing it's kid's profile. I am interested to find why a female want to give birth to a baby that has to be genetically healthy and special in society though her gene contribution is not much.
   yeah, one reason might be her gestation period is too long (9 months and difficult ) , so she might be developing love on her hard earned product.
   Even though it can be of any weak gene but why she want that gene to be healthy and intelligent, handsome etc.  May be she want to see her more loved own product becomes a target for other females.