"morals" in people seem to develop similarly to language
that is, memetically + example-based-statistically
in other words,
one's sense of good and bad is based on exposure to other people's senses of good and bad (particularly one's parents, but in general, one's community and local society)
which is similar to language/meaning acquisition:
seeing examples of chairs
...which is why synthetic rules / definitions fail to capture how morals / words are used in practice
ex. is a "hot dog" a "sandwich"?
ex. the impracticalness of Kantian ethics, the "immoral" conclusions of utilitarianism
but, since language and morality seem to share a similar way of spreading (memetically) and internalization (fuzzy, nearest-neighbor-example-matching)...
(a) ...maybe it's because they both (independently) based on some same foundation in our brain
(~ Chomsky's thesis that language requires certain brain structure)
(b) ...or, moral behaviour is directly a consequence for our capacity for language
which, could lead to the question:
do animals without language exhibit "moral behaviour"?
or, does extent of "moral behaviour" correlate with a species' capacity for language
some forms of psychopathy may be due to "lack of moral capacity" while still having "language capacity" which potentially counters this thesis (or at least, the (b) above)