The other one is prettier 😉
They’re called identical twins because their genomes are identical. But even though all of their DNA is the same, they clearly are not. The environment must play a role in how identical twins—and everyone else—uses their genes to become who they are.
Until recently, laboratory techniques have not been sensitive enough to detect how, and to what extent, environmental effects dictate the activity of genes. Now that we have the ability to do so, studies are examining variations in the activity of genes in identical twins to try to start unraveling the relative contributions of genetic and environmental effects.
Source: Finding gene activity differences in identical twins
The term “environmental” can be misleading. When most think of the term, the assumed context is what a person is exposed to after birth. But many of those environmental influences can occur during development before birth. Fetal alcohol syndrome, thalidomide… Something as simple as the relative diameter of the umbilical cord can have an influence on the concentration of chemicals needed for gene expression/methylation during important periods of prenatal development.
The author states: “…differences in expression between them can’t be explained by genetic sequences and must be due to environmental factors”. This used to be the working theory. In other words, it was fairly plausible that since twins are genetic clones, yet they often look different, it is most likely environmental factors that play a role in these differences.
In some cases, that is true. Epigenetics that has shown that a twin separated and raised under different conditions can have different protein expression. However, in the case of this paper, it might just be early stochastic noise.
In a cell, the way everything generally works is you have certain concentrations of proteins and other miscellaneous molecules. There is a certain level of “noise” – meaning collisions occur, and increase/decrease based on concentrations. By statistical random chance – “stochastic noise” – in early cellular development, you can get a higher level of protein concentration than in another cell at the same stage of development. In that moment it may not seem like much, but studies have shown these small and/or early changes to have very serious implications to cellular function once the cell has fully developed.
TLDR: We have found that early stochastic noise in a cell can have very different outcomes as the future plays out.