If that's the case how can a cis person be any of hetero, gay, bisexual, pansexual, omnisexual, or asexual. (The same goes for trans individuals.)
And how does asexuality fit into that"
I think you're confusing "desire" with the underlying orientation.
From
the AI overview on the subject:
... scientific evidence strongly suggests sexual orientation is largely innate, developing from a complex mix of genetic, hormonal, and prenatal environmental factors, rather than being a choice or learned behavior, though the exact causes are still researched and it's not determined by a single "gay gene". Major medical and psychological organizations view it as a natural variation, with biological influences shaping it before or around birth.
Key Factors Influencing Sexual Orientation:
- Genetics:
Genes play a role, but it's polygenic, meaning many genes contribute small effects, similar to height, not a single gene.
- Prenatal Hormones:
The uterine environment, including exposure to different hormone levels, is a significant biological factor.
- Epigenetics:
Modifications to genes (epigenetics) from factors like maternal diet or stress during pregnancy also play a part.
- Brain Structure:
Differences in brain structure linked to sexual orientation are also being studied.
What Science Says:
- Biological Basis:
Research points to a spectrum of biological factors present during early fetal development, making sexual orientation as innate as other traits.
- Not a Choice:
The idea that sexual orientation is a choice or result of upbringing (like childhood trauma) is outdated and unsupported by evidence.
- Complex Interaction:
No single factor determines orientation; it's a complex interplay of biology and environment (mostly prenatal), not social environment post-birth.
In summary, while we don't know every detail, science leans heavily towards sexual orientation being a fundamental, biologically influenced aspect of a person, established early in life, rather than a conscious choice or learned preference.