This news article about the Fundamentalist Church of Jesus Christ of Latter Day Saints (FLDS) kills two topics with one stone.
1. The often, yet unintended, destructive effects of crazy religious beliefs.
2. Evolution in action.
This was in the news a few years ago, about this offshoot of Mormons who forced teenage girls into marriage with much older men, essentially as sex slaves. The latest result of this cult is that children born of these marriages, often between cousins, are afflicted with a genetic disorder known as fumarase deficiency. This enzyme deficiency prevents brain cells from receiving sufficient nutrition causing mental retardation, frequent epileptic seizures, episodes of coma and other problems. The extent of the problem in this particular cult in indicated by the fact that half of the worlds known cases are in one particular town in Arizona, where this cult was situated.
Local historian Benjamin Bistline said 75 to 80 percent of people in the area are blood relatives of two men — John Y. Barlow and Joseph Smith Jessop — who founded the sect on the remote desert plateau in the early 1930s.
The irony here is that this sect, like most fundamentalist cults based on a strict biblical adherence, most likely scoffs at evolution. But most evolutionary biologists would probably agree that incest is a taboo across almost all cultures, precisely because in our evolutionary history, humans discovered that too much inbreeding weakened the population. The chance of passing on defective genes multiplies when relatives reproduce, because the mutated gene may be present in both parents, thereby increasing the odds of it being passed to the next generation.
Interesting explanation of the adaptive incest avoidance mechanisms here.
So what we are looking at is evolution in action. Take that, Ken Ham!
A nod to The Atheist Experience for the story. I wonder if Pharyngula will have something on this?
SPANISH INQUISITOR 
You said: The irony here is that this sect, like most fundamentalist cults based on a strict biblical adherence …
You can find plenty of incest between the covers of that dirty little book. Why do you think so many evangelicals are muhfuhs? (That’s how some people pronounced it in New York when I was growing up.)
It’s also worth noting that if the defective gene is a recessive allele rather than a dominant one, receiving it from both parents will allow it to be harmful.
Careful tagging this as “Mormons.” These people do not belong to the mainstream group of members of the Church of Jesus Christ of Latter-day Saints, who in large believe in evolution and are not inbred. You may consider Mormons a cult (whatever that means to you), but the two groups are as different as can be.
I realize that, but the FLDS is an offshoot of the Mormons, as the article made clear. They are not mainstream Mormons, but they take their theology from the original Church. They actually split some 70 years ago over the issue of polygamy.
It’s just a tag, and anyone looking up Mormons would find this post.
And yes, I do consider the Mormons a cult. I big one with mainstream pretensions, but a cult nonetheless.
RLDS is big in my town, they actually believe that the millinium will be here in Independance Mo. I’ll stock up on the beer for that one.