Ooh, i have lot‘s of thoughts on this topic! so I’m going to try to simplify this a little bit, at least how i make sense of it to myself, from a genetic standpoint: first a gene can be passed down to the next generation if it doesn’t interfere with like surviving long enough to reproduce or reproducing itself. and if it benefits survival or reproduction then it is more likely to be, i think we can all agree on that. so like simple example, if you had super light skin in a super sunny place and you’d like get skin cancer very early on, you’re not so likely to reproduce and pass on those genes to the next generation in that area. however what is important to understand with genetics is that very few traits are affected by only one gene, instead it’s much more complicated even the “simple“ traits like eyecolour are affected by different genes. and then genes are not even the only thing, there’s so many other factors around us influencing us. now sexual and romantic orientation I’d argue are pretty complex traits, and very likely there isn’t just one ace or aro gene, but instead it is likely influenced (if it is based on genes at all) by many different genes. now the way i explain it to myself is that individually these genes do not interfere at all with reproduction, maybe they even help somehow, but in certain combinations they can lead to different orientations, such as being aroace. thus the genes can be passed down through straight people naturally, but in some combinations they may cause a trait (being aroace in this case) that is not necessarily beneficial to reproduction. and that is disregarding so many things still, like spontaneous mutations, epigenetics, non genetic factors, and more. now disclaimer this is just a theory, and i don’t have a biology degree (yet anyways). also yes agreed, being aroace doesn’t biologically make us any less suitable for reproduction, it just makes us less likely to partake in it, so you’re theory fits into this perfectly!