One of the open (and unanswered thus far) questions in science is this: Why does the world look the way it does.
This fundamental epistemological question appears in numerous scientific contexts, some that have always intrigued me being the following: why all biological organisms have the shape they do? For example, why are there lions, tigers and bears along with humans and all other animals and plants one encounters on Earth, and have the form they do and carry out the functions they do at present and over the course of their evolution?
Why does water (and in fact any simple or complex chemical compound) have the chemical composition that it has, according to a chemist or physicist?
Why are there bosons, or any other elementary particles, above or below the scale an observer has been able to reach and observe thus far?
And more broadly: Why does the Universe (and all its elements), look to an observer like it does (and they do), and it has (and they have) evolved to exist in the manner, form and functions that it does (and they do), i.e., as it does (and they do) appear to an observer at our scale of existence and from our point of view?
These are basically existential/epistemological questions, since they involve "why's". Science usually is structured so that it poses questions starting with "how's". Yet, that doesn't necessarily imply that an epistemologist should not try to answer such "why's", without resorting to religion or untamed, undisciplined philosophy.