For as long as anyone can remember, the typical human pregnancy produced two fetuses. Near-identical twins, with one male and one female body. However, despite giving birth to two babies, a typical pregnancy also only results in one mind. This mind is shared between the two bodies as a form of a localized hivemind.
There are a few ways that this has affected cultures. Some cultures do assign specialized roles for the male or the female bodies, but this is enforced with the same kind of strength that some cultures assign specialized roles for the left hand and the right hand. Many of these cultures don’t strictly enforce these roles and treat them more as a personal preference. For example, most people might prefer doing yard work with their male body, but for some people doing it with their female body feels better. Other people might be effectively ambidextrous and use both bodies for any tasks they have. Typically, however, they will have to reestablish muscle memory for each body because the bodies are slightly different.
There are important implications of this for military operations. Some militaries will specifically separate the bodies of their soldiers. Having the larger male bodies on the battlefield while the female bodies are clustered in command centers allows for quick communication between separated elements. Such forces have been described as eerily quiet on the battlefield since they have no need to be shouting orders or sounding horns. Units will simply silently move in unison.
The other approach is to keep both bodies of individuals together. This allows for greater combat prowess of the individuals. Typically, two single-body fighters will struggle greatly against a solitary dual-body fighter even when allowing for their larger overall mass in the fight. The level of subconscious coordination between two bodies that share a single mind that has specifically trained for fighting in such a way is difficult to overcome.
The first style of military tends to be better suited for large-scale conflicts where coordinating disparate elements can be difficult. The second style does better in more narrow scopes where a single melee can decide the war.
In terms of fashion, most cultures encourage their people to have the outfits of both bodies coordinated and matching. However, there is still some degree of expecting a different cut of outfits on the different bodies. Especially in cultures that have a stronger expectation of the different bodies being used for different kinds of tasks.
Birth defects do occur. Occasionally, a solitary baby might be born or one body might be stillborn. This is treated as a form of disability similar to children born without complete limbs. Some cultures shun them, but others will give them the support they need to live as close to complete lives as they are able. People who have one body die later in life are similarly treated as though they have been maimed, though they are less likely to be shunned for it. Especially if they lost one of their bodies doing something considered particularly honorable in the culture (such as dying in combat for a warrior culture).
Another birth defect is where both bodies are the same sex. Again, some cultures shun such people and some will even demand that they pick one to be the male body and one to be the female body regardless of the physical biology of the bodies. However, other cultures will be more accepting of this condition. A few even celebrate it and consider sets of identical twins to be blessed by the gods. The idea being that they can be more specialized in filling the roles expected of whatever sex they are born to. For example, warrior cultures prize identical male twins as great heroes on the battlefield. As another example, cultures, where the female body is expected to be the main one taking care of children, might prize identical female twins as being great homemakers and even educators for society as a whole.
Sometimes, someone will decide that they prefer one sex over the other and will attempt to transition the body that doesn’t fit to match their preferred gender. The level of commitment that individuals have to this differs. Some will simply dress and groom one of their bodies as the other sex while refraining from using their non-preferred genitalia. Others will undergo extreme surgical procedures and hormone treatments to transition as much as possible. Again, some cultures reject this, but others are more accepting. For societies that prize those born as identical twins, they may see someone who sacrifices one of their sexes as filling a similar role. The only difference being that while those born with it are blessed by the gods, these people have made a conscious choice and are working hard to achieve it.
Another birth defect is the occasional set of twins where the hivemind connection between them is imperfect. Sometimes, the connection is partially there but they share a subconscious mind instead of the full conscious mind. Other times, they only get vague impressions of their twin or have no detectable connection at all. While from the perspective of these twins, they might often see themselves as separate people from a cultural standpoint they are treated as a single person. It is seen as a psychological or neurological disorder.
Therapy will be offered to help them develop as much coordination as possible with varying degrees of success. It does sometimes pose a legal issue when the twins want to go separate ways or if one commits a crime without the knowledge of the other one. The law regards them as a single person even if they don’t actually act as one.
On rare occasions, triplets or even larger sets might be born. While technically a birth defect, it is rarely seen as one. They have great advantages over other people. In many cases, they get all of the advantages of identical twins specializing in particular tasks without having to sacrifice having a body of the other sex. In rarer cases, the triplets might all be identical resulting in being socially regarded as an even more extreme version of identical twins. Even societies that encourage identical twins to pick a male and a female body often accept triplets or larger sets as special cases. Of course, the typical female body is not designed for handling that many babies at once. It is often a great struggle for the mother to bring them successfully to term and has a high maternal mortality rate. This has served to keep it rare even though the chance for it often runs in families.
Culturally, no society even has the concept of homosexuality vs heterosexuality. Because a typical pairing is two female bodies and two male bodies, it is seen as perfectly normal for an individual mind to be attracted to both. Amorous affection between same-sex bodies is seen as no different from non-procreative amorous affection between opposite-sex bodies. Even the most prude cultures acknowledge that some affection is normal between married pairs even if they encourage a focus on procreative sex. Most cultures accept that whatever two married sets of twins do together is perfectly fine. More sexually liberated cultures are accepting of non-married sets performing sexual acts together. In fact, some cultures encourage male/male or female/female engagements for casual sex because of the lack of a risk of accidental pregnancy. It is seen as even more effective than the method of sticking to non-reproductive orifices.