Rather than use a lot of space on this page, here are links to some good articles answering that question:

Scholarly Articles by Dr. Robert Gagnon

The "conventional wisdom" of our culture is that homosexuality is genetically determined and unchangeable. You will hear many in the media, especially gay activists, make statements such as "Gays and lesbians can no more change their sexual orientation than their eye color." Or, "homosexuality is as natural as being right or left-handed." 

These arguments are often politically motivated and are lacking in any solid scientific or statistical evidence. No one has ever been able to determine if the observed differences in brains of heterosexual and homosexual males caused the same-sex attraction/behavior or were a result of their sexual practices. And many question the interpretation of the various identical twin studies.

In September of 2003, I wrote about the discussion about "change" that was going on among Exodus member ministries. Some folk on both sides of the debate would like it to mean - no longer having any same-sex attractions, getting married to someone of the opposite sex and having many children. But that doesn't always happen, though Scripture (1 Corinthians 6) suggests that the potential for it is real and obtainable.

A lot of Christians have experienced a major shift in their desires to the point that they can have a satisfying relationship with the opposite sex. But they also honestly admit that as with any sin, there may be times of temptation - to greater or lesser degree. Others experience little to no attraction to the opposite sex, but live fulfilled, chaste lives in obedience to God's will for human sexual expression. They don't believe sexual intercourse is a "right," or the be-all and end-all of life. Nonetheless, all of the above is "change."

Transforming Congregations would prefer to emphasize instead the Biblical concept of "sanctified sexuality." Sanctification is a process with successes and failures, and not perfectly realized this side of heaven. 

Several brave (and wise) people are now blogging about their journeys of sexual sanctification. Their links are below.

Disputed Mutability

Adventures of a Christian Collegian

As Were Some of You

How many homosexual people are there?

Many Americans believe that homosexual people make up about 10% of the population. This figure is actually a "rough average" resulting from sexologist Alfred Kinsey's work in the late 40s and early 50s. (Kinsey's work has been critically challenged because of methodological flaws and bias. See http://www.drjudithreisman.org/ for more information.) However, more recent studies in the United States, Canada, Great Britain, the Netherlands and New Zealand suggest the number may be substantially lower - from 1.3-2.8% of men and 0.7-1.9% of women who identify exclusively as gay or lesbian.*

Statistics could vary substantially depending on whether or not respondents are asked about identity - Are you gay? - or behavior - Do you engage in this activity? Cultural considerations can also influence outcome, some ethnic groups not identifying as "gay" even if engaged in homosexual activity.  And bear in mind that all such studies are based on self-report and primarily reflect the experiences of Westerners.

One Internet blogger summarized by saying, "That's why we see numbers all over the map. Language, identity, culture, self-conceptualization, and simple honesty all hinder our ability to come up with numbers that are remotely accurate."

As with the above issues of cause and change, discussions about numbers can be politically motivated. And while they are of interest to social scientists and the therapeutic community, statistics have little to no bearing on moral considerations.

*Gilman SE.  American Journal of Public Health. 2001; 91: 933-9

Aaron DJ et al. Journal of Epidemiological Community Health. 2003; 57 :207-9

Statistics Canada - www.statcan.ca/Daily/English/040615/d040615b.htm

Mercer CH et al.  AIDS. 2004; 18: 1453-8

Sandfort TG et al. Archives of  General Psychiatry. 2001; 58 :85-91

Fergusson DM et al.  Archives of  General Psychiatry. 1999; 56 : 876-80