Biochemical Individuality by Roger Williams [1] is an amazing read. It discusses a wide variety of "unusual" human physiological characteristics, including bones that only occur sometimes.

One hears the refrain "everyone is unique". The thing is, technically you can say "every factory made part is unique" at some level. But humans are much more unique on many more different levels, than any human-made-machine (things like bone density or blood saltiness vary widely. Indeed, very few measures are uniform for everyone).

The remarkable thing is how the different parts of a living thing can still function well with that capacity to vary.

[1] https://www.amazon.com/Biochemical-Individuality-Roger-Willi...

in biology reliable layers of abstraction do not yet exist.

In biology, reliable layers of abstraction do not exist. Period.

Biological technologies may arise with enough flexibility and processing power to deal with this situation. But situation itself won't change. Life simply evolved without fixed boundaries to its layers of abstraction. Every bit of evidence we have points to the genetic code as being more akin spaghetti coded assembly language than to any human-comprehensible programming language. Why would the genetic "programming" system respect any layers of abstraction understandable by humans? Life's been chugging away with 4 billion years of "whatever works".

Roge J. Williams' work early in the 20th showed how in just about every single biochemical system in the body, something like 20+% of the population and that with these outliers not correlating, every person's biochemical system actually work in somewhat unique fashion. That is hard manage and control from an engineering perspective, to say the least. See http://www.amazon.com/Biochemical-Individuality-Roger-Willia...