Scientists have discovered mystery snippets of mammal DNA that have survived eons of evolution and yet have no apparent purpose. The finding reveals just how much we don't know about the secrets hidden in our genome and that of other animals.

Most genes change throughout evolution via mutations; useless ones eventually get weeded out of the population while the helpful modifications take hold. However, about 500 regions of our DNA - the body's instruction code made up of base pairs of molecules - have apparently remained intact throughout the history of mammalian evolution, or the past 80 million to 100 million years, basically free of mutations.

....

The researchers call these mystery snippets "ultraconserved regions," and found that they are about 300 times less likely than other regions of the genome to be lost during the course of mammalian evolution. Bejerano and his graduate student Cory McLean detailed the finding in the Oct. 2 issue of the journal Genome Research.

The fact that these segments haven't been weeded out by natural selection implies that they serve an important function in mammals. Yet mice in the lab bred to lack these DNA strands appear healthy and don't seem to be missing any vital genes.

Different genes have been noticed to mutate at different rates.  Some parts of the gene that code for haemoglobin, for example, are conserved from species to species.  On examination, they turn out to code for critical parts of the molecule. Other genes, such as histone genes, produce proteins that are intimately involved in handling DNA, and any change in the DNA sequence is very likely to break the system.  So histone proteins resemble each other very strongly even among distantly related species.

In other portions of the genome, such as the "junk DNA", mutations pile up at a much faster rate.  Because junk DNA doesn't have any function, changes in the sequence have no effect.  Over time, mutations pile up at what is considered to be the "neutral rate".  If you have two species that have diverged recently, the junk DNA will show differences that result from these accumulated mutations.

This theory says a few things about different stretches of DNA.  Cave fish have lost their eyes since their ancestors wound up in the cave.  The genes that are responsible for building eyes have been identified.  You'd expect that, since these fish don't use eyes, the genes that code for them would start mutating at the neutral rate.  Instead, mutations pile up at a slower rate.  Somehow, the proteins involved in these non-functional eyes matter. There are some random mutations that are being screened out of the population because they make their carriers les fit.  They must be serving some purpose independent of vision. 

The puzzling thing about the "ultraconserved" regions of DNA in humans (and mice, and other species) is that they don't appear to have any function.  And since mice can be bred which lack those pieces of DNA (so-called "knockout" mice -- that portion of the DNA is knocked out), we can see what difference this change makes.  It doesn't seem to make any difference.  So why these sections of DNA should be hanging around for millions of years becomes even more puzzling.  They must be important, just not in the short run.

The Supreme Courts of the States of Massachusetts and Delaware Connecticut have decided to order the legal acceptance of same-sex marriage. California's Supreme Court has done the same, and same-sex marriage advocates are fighting tooth and nail against a Constitutional amendment to undo this decision. At least a couple of countries in Europe have legalized same-sex marriage.  

Advocates of same-sex marriage challenge opponents to produce a smoking gun.  They ask, "How will legalized same-sex marriage affect your marriage?" The point is, when same-sex marriage is made legal in a State or country, civilization doesn't immediately collapse. The sky doesn't fall, the seas don't rise, the mountains don't belch forth volcanic clouds, plagues of locusts don't ravage the land. To all appearances, the health of the society is unaffected.

Yet the number of societies that have historically supported same-sex marriage is vanishingly small. It's hard to find any legal code allowing for it.  Religious law doesn't support it in any of the major religions.  Philosophers of the enlightenment did not advocate same-sex marriage.  Given this lack, I'm inclined to wonder if it's more than just coincidence.  Maybe societies that support same-sex marriage are less fit in the long run than societies that don't.  Like the ultraconserved regions of DNA in animals, you can eliminate the laws against same-sex marriage in a society and no adverse change is immediately apparent.  But in the long run, we may wish we'd retained them.