I'm familiar with the fact that homosexuality used to be considered a mental illness by the American Psychological Association. 

I'm also interested in how the mental disorders of the DSM can be seen as social constructs rather than proper diseases or illnesses with their own underlying pathologies and etiologies. Much has been written about that, the social construction of mental illness.

But I just became familiar with some writings about homosexuality being described as a social construct. 

There is homosexual behavior. That is, behavior between individuals of the same sex which is sexual in nature. But because people have engaged in this type of behavior, or that some do it often and prefer it over heterosexual behavior, does that mean that there is something called homosexuality?

I'm of the belief that there is such thing as homosexual behavior, but I don't think the existence of homosexual behavior is evidence of, or the product of, something that could be called homosexuality.

Many have even tried to find a biological basis for homosexuality, but to no avail. Attempts to find causes of homosexuality have failed. To define homosexuality by some biological characteristic have yielded nothing as well.