Why are we so different from one another?

It is the casual question at the end of this story that caught my attention (emphases mine). The story itself is quite remarkable. Once upon a time I was taught "one gene, one protein". That turned out to be untrue, though a useful initial simplification. The relation between genes and proteins (the builders) is many to many, not many to one or one to one. Later I was taught that nuclear DNA was the fundamental basis of heredity. Then we learned that mitochondria had their own DNA and that prions could carry encoded protein altering directions without DNA. Until today most of us thought that animal heredity worked through DNA and histone imprinting alone. Now that may not be quite true either...

BBC NEWS | Science/Nature | Spotty mice flout genetics laws [jf, aka: RNA directed paramutation in mice]

... Researchers found that mice can pass on traits to their offspring even if the gene behind those traits is absent.

The scientists suggest RNA, a chemical cousin of DNA, passes on the characteristic - in this experiment, a spotty tail - to later generations...

... They found the mutant Kit gene produces large amounts of messenger RNA molecules (a type of RNA which acts as a template for the creation of proteins) which accumulate in the sperm of these mice.

The scientists believe the RNA molecules pass from the sperm into the egg, and they "silence" the Kit gene activity in the offspring - even those who do not inherit a copy of the mutant gene. Silencing the activity in this gene leads to a spotted tail...

...The phenomenon whereby the characteristic of a gene is "remembered" and seen in later generations, even if that particular version of the gene is no longer present, is called paramutation.

It has previously been identified in plants, but this is the first time it has been shown in animals together with a proposed mechanism - if the explanation is confirmed in future experiments...

Could transfer of RNA in sperm explain other so-called epigenetic phenomena as well?

... "A particularly intriguing possibility," he writes, "is that such RNAs regulate other non-genetic modes of inheritance, such as metabolism or behavioural imprinting."...

... "This brings valuable information about modification of our genome," said Minoo Rassoulzadegan, "and perhaps this research may eventually help us to understand why we are all so different from each other."

Did you know that biologists are quite puzzled about why we humans, who seem so similar at the DNA level, are so different in practice? I'd thought that research in the control of gene expression suggested that tiny changes in DNA control could produce large changes in protein expression. It appears the question is not so settled.

Biology reminds me quite a bit of physics. When I was a child we had protons, neutrons, photons and electrons (at least in popular science books for children). Shortly thereafter there were bazillions of particles. A simple story became rather complex. So goes biology ...