I'm not at all sure what heterosexuality has to do with the topic of the Man Box. Clearly, thousands of years ago humans didn't have IVF - they had to reproduce the old fashioned way with genetic material from both parents - who have different "plumbing" - that's how basic biology works in nearly all animals - and that continues today for most humans despite modern reproductive technology. And at the same time, thousands of same-sex couples have children in other ways, although they are are only a tiny percent of the population (about 7.2%) and not all same-sex couples want to reproduce.

Aside from the science I've already presented, it's clear from just looking around at the world that you cannot truly tell who someone is from their sex alone. There have always been women who were big game hunters and warriors, and scientists and all sorts of things not "coded" for their gender, just as there have always been men doing things not coded for theirs. And what is coded for a particular gender is different from culture to culture and from time period to time period. Which is why we say that gender is a social construct (as distinct from sex, which is biological). And mostly, what gender codes have been used for in the West in the past 5k years is to artificially marginalize and oppress women by creating myths about what they are inherently like and what they can and can't do based on their biology.

And when you look at cultures where people largely don't pay attention to what is coded for a particular gender, they not only do just fine, but they tend to be a lot happier because no one is coercing them to be anything in particular. In fact, in most indigenous cultures there are anywhere from 3 to 7 acknowledged genders. I don't see why letting people be who they naturally are is "a Pandor's box" of anything. To support that people ought to be forced to be something other than who they are for their own good is just the worst kind of social pressure I can think of. And, what we see is that it causes a lot of pain because it comes with a lot of policing and bullying to be something other than who you are - which demonstrably often leads to depression, substance abuse, and suicide. What exactly is the upside of that?

We're all a blend of Yin and Yang traits and although what that blend is may be quite individual, in the end we are all just human beings. Why isn't that enough? This talk of a vacuum is just silly. There's no such thing in a society. There are all sorts of examples of all sorts of men (and women, and non-binary folks and intersex folks) all around for a child to observe and learn from - to say nothing of whatever is just naturally there for a child. I honestly just have no patience for the idea that someone needs to show you who you are - because that's inherently coercive. No, they need to support you in figuring out who you are for yourself.

The Australian Aboriginals have a much more gender divided culture than most other indigenous societies, but nonetheless, when the men go off for sometime to participate in religious ceremonies that women are not included in, they are able to do all the things that women usually do at home, and the same for the women. While the men are gone, they just temporarily take up the "men" roles of hunting and such because it wouldn't be very evolutionarily adaptive for it to be so deeply divided that someone could not survive without their complimenting gender around to do certain things. This is true for all of pre patriarchal history - it's how humans survived. I've been meaning to write a story about this for some time. I guess it's time to get on that.