>>How do you know? We do not know the genes associated to sexual orientation (yet). Anyways, a gene defect can occur spontaneously, with no family history. So why would this be different?
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>Does not make any sense. You claimed that it is a scientific fact that people are born one way or the other in regards with their sexual orientation, but the gene responsible for this has yet to be discovered? Then it is not a scientific fact, just a theory, right?

First of all, I did claim that there is a firm scientific basis/proof that you are born with it. Scientist are convinced that at least genes play an important role in it. Additionally some prenatal hormones and other environmental circumstances can play a role in it. Since there is a lack of any scientific proof that you develop homosexuality later in life, what other conclusion you want to draw?

If you read the article link I gave earlier, it will become clear.

Second, we know that the problem of heritable cancer is somewhere in the genes, but we still are looking for which ones. Most often it is not a single gene, but combination of genes which makes it much more complicated to pin it down. Can we agree that even if we do not know exactly which genes are responsible for it, hereditary cancer is proven to exist?