Comment by roughly

Epigenetics is one of those things that seems wild until you pull the camera back a bit. A cell is affected by and responds to its surroundings - this is not controversial. In eukaryotes, this is usually done by way of altering gene expression - up- or down-regulation by means of chemical markers on the cell’s DNA which are created or removed by enzymes which are activated or deactivated by certain substances in the cell or its environment - in other words, the cell’s environment affects gene regulation within the cell by traceable mechanisms*. All cells, save at least one, are descendent of other cells, and cells split by meiosis, in which the chemical environment within and without the cell is shared by the “descendent” cell - so of course this happens with human embryos as well. Of course the expression of your genes is affected by what happened to your parents (well, your mother, at least), because gene expression is affected by what happens to a cell and you are made up of a lineage of cells descended from your mother’s cells. If you ask how one organism could be affected by something it didn’t experience, sure, that could be a quandary, but looking at a line of cells and wondering how later ones could be affected by environmental pressures on earlier ones isn’t nearly as much of a mystery, and we’re all just extended cell lineages.

(As if first time mothers didn’t have enough to worry about - stop stressing so much, it could lead to long-lasting irreversible changes to your fetus!)

* Standard biology disclaimers: this is not the only way this happens, this varies across species and time, nature has no master plan. “Some of the time some genes have some amount of their expression modified somewhat by some mechanisms that are somewhat responsive to some part of the cell’s environment sometimes.”