Gender is a social construct designed around sexual dimorphism
Females of the species are equipped to and (before the development of birth control) likely to carry children, which inconveniences them physically for several months. Historically this was somewhat frequent. This caused a selective evolutionary pressure to concentrate traits compatible with said inconveniences on the female chromosome, and concentrate traits less compatible on the male chromosome. This created the kernel of gender roles, which themselves evolved over the years under the resulting social pressures of gender interplay.
Consequentially, women traditionally fill roles that can be accomplished while pregnant and/or breastfeeding (cooking, cleaning, childcare, weaving, sewing, etc) and men traditionally fill roles which are particularly difficult to do while pregnant and/or breastfeeding (hunting, farming, other strenuous labor, etc). These were reasonable adaptations that were broadly useful for quite some time. So in a sense, we’re born with it.
Recently, developments in housekeeping (breast pumps, formula, automatic appliances, public schooling and childcare, affordable industrial textiles, etc) and labor (the transition from physical to mental work) have made the biological differences between males and females less relevant in fulfilling social roles. What’s more, social roles have changed so much anyway.
Personally I think we’re getting to the end of the usefulness of gender as a social concept.