Here is an article from Trayce Hansen, Ph.D. She summarizes the evidence on homosexuality in response to proposed changes to a California school board’s curriculum that would promote and normalize homosexual behavior.
ENVIRONMENT IS PRIMARY FACTOR IN DEVELOPMENT OF SEXUAL PREFERENCE AND GENDER IDENTITY
Decades of research confirm that sexual orientation and gender identity are not inborn but are primarily shaped by environmental influences during childhood and adolescence. The proposed school curriculum will affect the sexual preference and gender identity formation of some children exposed to it because it teaches that all sexual and gender variations are equally acceptable. Sexual preference and gender identity formation are fragile developmental processes that can be disrupted and altered by environmental influences such as the lessons in the proposed school curriculum.
SEXUAL ORIENTATION IS NOT INBORN
Many people continue to believe that sexual orientation is inborn, although that is not true. Extensive, worldwide research reveals that homosexuality is predominately influenced by environmental factors. For instance, recent large-scale studies compared rates of homosexual behavior in sets of identical twins. If homosexual behavior were inborn, every time one identical twin was homosexual, the other identical twin would also be homosexual 100% of the time. But this is not what the research revealed. Rather, every time one identical twin was homosexual the other twin was homosexual only 10% or 11% of the time. Homosexual behavior is clearly not genetic.
In fact, an accumulation of extensive research utilizing millions of research subjects finds that environment, not genetics, is the main factor in the development of non-heterosexual behavior. (To review these research studies see references 1-4 listed below).
[…]NON-HETEROSEXUAL BEHAVIOR LEADS TO INCREASED RISK OF PSYCHOLOGICAL AND PHYSICAL DISORDERS
Sadly, the research is also clear that individuals who adopt non-heterosexual lifestyles are more likely to suffer from a host of negative outcomes including psychiatric disorders, alcohol and drug abuse, suicide attempts, domestic violence and sexual assault, and increased risk for chronic diseases, AIDS, and shortened lifespan. Schools should not affirm and thereby encourage young people to adopt lifestyles more likely to lead to such devastation. (To review these specific studies see references 5-10 below).
GENDER IDENTITY DISORDER IS A PSYCHIATRIC DISORDER THAT SHOULD NOT BE NORMALIZED TO CHILDREN
The proposed school curriculum also teaches that transgendered lifestyles are a healthy and acceptable alternative to the norm. That is not true. Many transgendered individuals suffer from a psychiatric disorder known as Gender Identity Disorder (GID) that is recognized by the American Psychiatric Association as a mental disorder in need of psychological treatment… (For a thorough understanding of Gender Identity Disorder, see reference number 11 below authored by world-renowned GID experts).
Read the whole thing here, at the Ruth blog. The references to medical research publications are at the bottom of the article. The majority of the research papers cited are from 2005 to the present.
You may also be interested in a recent post discussing why people oppose same-sex marriage.