There is a VERY interesting article in the August 2014 issue of Scientific American called "A New Kind of Inheritance."  The topic is epigenetics - having to do with inherited traits that do not require a mutation of a gene.  I normally skip over the "medical" or "organic chemistry" articles because they tend to bore me - however, this article is something else again. 

In brief, it turns out that there are things (such as methyl (CH3) radicals) that attach to the DNA molecules of the chromosomes that are used to turn on and off the expression of genes.  (They impact the phenotype or observable characteristics of the organism).  These gizmos are what allow things to happen such as a stem cell turning into a heart cell rather than a toe cell.  These markers get passed along with the chromosomes to the daughter cells during cell division. Changes to them during cell division also seem to cause many of the changes associated with aging.  Most of these things get stripped off during the period of transition between being a stem cell and being a differentiated cell - but not all are removed.  Some stay in place so that they can be passed on to the next generation of individuals if they happen to be on the gametes (sperm or egg) prior to forming the zygote (the first cell after conception). 

Thus, if something changes the configuration of these things on the gametes, those changes can pass to the offspring and cause changes in how the chromosomes are expressed (resulting in changes to the phenotype), without requiring changes to the chromosomes (mutations).

This is all vaguely interesting until you ask the questions of what can cause these changes, and what kind of outcomes do they influence.  It turns out that a whole lot of things can make these changes - such as exposures to all sorts of chemicals and pesticides (such as DDT and others), stress (such as near starvation episodes), and others.  Lots of things can make the changes - especially lots of chemical things that we have introduced into our environment over the past couple hundred years.

The effects are wide ranging, but a couple of them that have been pretty clearly identified are obesity and diabetes.  There are also changes in fertility, success during pregnancy, social behavior, memory, cancer, high blood pressure, heart disease - the list goes on and on and on.  Interestingly, the list seems to coincide pretty nicely with the "epidemics" being experienced in the "developed" nations, and that are now becoming evident in the "undeveloped" ones. 

That is all sort of ho-hum background information.  Now for the interesting part of the story.

It turns out that these changes are persistent from one generation to the next!  If a mother is exposed to one of the things that cause these changes during the 7th to the 18th week of pregnancy, the changes can occur to the fetus' sperm or egg cells (the lifetime supply of which are produced during this period of time).  The individual formed from that fetus is unlikely to show the signs of the epigenetic changes because their stem cells were already formed and cell differentiation was well under way.  HOWEVER, their offspring will show the effects.  The changes effect the grandchildren of the exposed person, not necessarily their children.  Not only that, but it keeps showing up in subsequent generations.  The changes persist for many generations. So far they have tracked this through five generations and have not found an end to the string.  Thus it is entirely possible that I am obese because of an exposure that my great-great-grandmother had in 1860 - or my great-great-great-great-grandmother had in 1780; or because of an exposure that my grandmother had in 1917 when my father was born, or 1908 when my mother was a fetus. 

I have always thought that it is impossible to inherent traits because of things that happen to our parents unless those things cause mutations.  Not only did I think that, but the rest of the scientific community also thought that.  The only ones that thought that environmental impacts could cause lasting inherited changes were kooky folks who believe in these sorts of "unscientific" theories, and other "strange" beliefs (from the point of view of a scientist) such as astrology. It turns out that while they didn't have an scientific evidence pointing to what might cause such persistent changes, they were correct. This effect was discovered in 2005 as the result of an error in a lab experiment.  Someone messed up and let a couple of rats find each other when they were supposed to be separated.  Since the experiment was thus destroyed, they decided to wait and see what would come of it in the future - and much to everyone's great surprise, the field of epigenetics was the outcome.