There's a great deal of scientific evidence to support a biological factor.
I don't believe that's true. What seems to be emerging more than anything is there seems to be a wide variety of contributing factors. Biological factors may make one more susceptible to external influences than others, but I'm not aware of any accepted theory that biology alone is supported.
I'm interesting in knowing your definitions of nature and norms.
My view is nature is the essence of something.
Norms are accepted behaviors, so they are learned. I subscribe to natural law, so I believe for them to contribute to true human flourishing they should be informed by natural law (which admittedly has certain limits, which is expected being that our minds are limited).