Identical twins aren't so identical, not even their brains

That's been known to be true for some time. Depending on when the single fertilized egg divided, identical twins can have separarate amniotic sacs, umbilical cords and placentas, the same sac, the same cord as well, or even the same placenta.


And now, we're learning that identical twins may not have entirely the same genetic makeup, not even in brain cells.  As a result, twin studies for illnesses, behavior, etc., may be called into a bit of question, and future twin studies more carefully controlled for subjects.

At the same time, the authors occasionally slip into quasi-teleological language while wondering why evolution "allows" this. Their proposed answer as to why this may happen is interesting, but could serve to have that language nuanced better. Also, even if you allow for the teleological/personifying language, that may not be the reason why this happens; maybe epigenetic events are at least partially involved, even with identicals. After all, they don't share 100 percent the same environment.


And, it may turn out that on a statistical average, such transposition isn't favorable or unfavorable, and that we're talking about a ramped-up genetic drift. Or maybe more modest transposition was more favorable, and now, the degree of favorability has lessened. From what little I know, genetic studies like this are kind of like studying individual frames, or at best, snippets, from a movie, when the backdrop for the movie may have been radically different at another point.

Nature VIA nurutre

If you haven't kept up with recent research on heredity, population genetics or anything similar, the new Time has a GREAT story on epigenetics. Look it up and read it. Then throw away any simplistic ideas you have about "genetic inheritance."

If you are familiar with the basic idea of epigenetics, some of the newest findings may still surprise you, such as the rate of influence, the depth of influence, and more. Giraffes' necks aside, maybe Lamarck wasn't so wrong. Certainly, Stan Prusiner looks ever more right on prions, in light of stuff like this.

Obviously, we are nowhere near the end of discovering what epigentic findings mean. But, I think we can put paid to a few of the more outlandishly positivistic ideas of late 20th-century genetics.

Individualized medicines? Not likely to happen, and certainly not any time soon. You'd have to check at least some epigenetic as well as genetic factors. The price for that and an even higher level of individualizing the medications, would seem to pretty much rule that out.

Insurance, insurance, privacy, snooping, pre-existing conditions? All in a new realm now.

Drug testing? Some lawyer will raise an epigenetic argument at some point, whether it's legit or a red herring.