Imagine a species almost identical to humans, with one exception. All sperm contained both X and Y chromosome, and every child has the potential to develop as either sex. However, the mother has some form of control to select the sex of the child during early development, say through controlling rather or not estrogen was introduced in the womb during early development to trigger female development.
This species evolved this way from the start, they are not using technology to control this change. As such their culture and psychology would be evolved around the presumption that sex choice was possible.
I'm wondering how the species would evolve, and in particular what it would do to their gender roles. Would gender roles be stronger or less stringent in a world like this? Would gender roles otherwise tend towards the same pattern as we have now, or would this somehow modify the actual role of gender?
I'm interested in both the culture and evolutionary psychology, the nature and nurture sides of the gender roles.
I remembered an interesting fact about evolution and mating strategies. In the more common mating systems, where males compete for females, the desire for male vs females depends on the 'strength' of parent/child. Since males have to compete for mates, and thus a weak male will likely never get to mate while a strong male may get dozens of mates, there is limited benefit in having a son who is going to be weaker, but massive benefit to having a son if he is likely to be particularly strong. However, since females will have no trouble finding males who wish to mate with them (it cost a male almost nothing to mate, and thus he will mate with a 'weaker' female) having a daughter who is weaker is not as disadvantageous; at the same time a 'strong' daughter doesn't benefit from her strength by having much of an increased mating opportunity, since she will likely have one child per mating-season regardless of her strength if she survives. Studies have even shown some species have very slight favoring of male or female children depending on various measurements of 'strength' or health due to this.
Pre-culture humans with conscious control of sex of the child would likely evolve to recognize this principle on some instinctual level. Younger mothers, unhealthy mothers, or mothers who had lower social status may be more prone to choosing females, while high status mothers are prone to males based off of this principle; which would likely evolve as an instinctual predisposition prior to cultural development. This would in turn likely have many interesting effects on gender roles once culture had developed. Any thoughts on what kind of effect it may have?