Incest causes DNA to go wonky. Evidence provided by Mother Nature herself that incest is not the right way.
Yes, well... mother nature also tells us that we should die following that logic, now doesn't it?
Well, to be honest it's more of a case of DNA being lazy. Our DNA doesn't care, it just has to pass itself down. It doesn't care if we live or die or what the next generation's like.
Fact of the matter is, as per an evolutionary standpoint, it's just easier for DNA to evolve to pass on itself with death than make the complex changes needed to stop aging. It does its job whether we die or not.
So, is that mother nature telling us death is the right way? No, no it's just telling us that it happened to occur that way because it's more efficient. It's harder for some creatures to pass on their genetic material, and thus they've evolved to have longer lives. And some, it's very easy and so they have very short lives. Of course, it's terribly more complicated than all that. If you're really interested in the subject
you can check out this video. It's pretty easy to understand.
And you know, incest in itself isn't all bad, on the genetic front. We do pass down certain traits. As you know, many breeds of dogs are inbred, which results in certain features becoming more prominent. It's a method of evolving, really... each iteration will become stronger and we can focus on certain features. It has been at work for awhile now... as many of you may have heard, as a species we were once much smaller than we are now, and other things as well. Incest just speeds up the evolutionary process, so to speak. Bad results invariably happen, anyone that's bred dogs especially knows that. But sometimes you end up with something totally amazing, and you could base an entire new breed off of that. In nature, y'know, it would take thousands and thousands of year for this type of selection to occur, but we can speed up the evolutionary process ourselves. For the better, or perhaps, for the worse. But we speed it up nonetheless.
As for examples of areas where this occurred... The Pingelapese Islanders, actually.... they were founded by a couple thyphoon survivors and as a result about 5-10% of the population is color blind. Other examples.... Amish, Ashkenazi Jews and European royalty (and well, I seem to remember the entire population of Iceland being very degenerated genetically due to incest because they were very isolated).
See
this article for some explanations. Basically, incest is bad
now because recessive diseases are everywhere. But thousands or hundreds of thousands of years ago, it wouldn't have been a problem at all without them present.
Northern Europeans have a higher incidence of CF. The Japanese have a greater risk of getting meningococcal meningitis. Africans have a higher incidence of sickle cell anemia. Southeast Asians have a higher incidence of alpha-thalassemia.
If our original two people didn't have these diseases, then where would the disease genes come from?
Well, new mutations happen all the time. Most are harmless, a few are harmful, and a very few are beneficial. (For a beneficial one, think about the recent mutation that let's a quarter of the world's adults enjoy an ice cream cone.)
With lots of people over a long period of time, some bad mutations are bound to develop. For example, we see them happening today in a disease called neurofibromatosis (NF). About half of all new cases of NF are because of new mutations.
What we've discussed for genetic diseases is also true for other things like genetic traits. Our ancestors in Africa were most likely dark skinned with brown eyes. A group that reached Northern Europe developed mutations that gave blue eyes, red and blonde hair, and light skin.
These same mutations could have developed in Africa. In fact, they probably did but disappeared because people with fair skin may not have done as well there.
In Northern Europe, these mutations were actually beneficial (probably to get enough vitamin D from the sun). This meant that once the mutation popped up, these people did better and so eventually, most Northern Europeans ended up with light skin.
Oh and uh... regarding one of my earlier statements. I kinda took the easy route on that, in saying siblings of the same gender couldn't produce offspring together...
Fact is, they technically could very soon... So could the LGBT community.
In conclusion... it's not so much that it's "bad" as that it's easier on a genetic level to not compensate for it since it's quite rare in modern society. However, if it became a very common occurrence over thousands of years, then well.....
milk. Eventually things happen.
