Why were almond trees domesticated for consumption but oak trees were not?From "how to make an almond" in Diamond's book Germs, Guns, and Steel

The answer to this is found on p. 129 in my book. 
Basically, the answer is that bitterness in almonds is controlled by only one gene.  In
oak trees, by contrast, the bitterness of acorns is controlled by many
genes.

The reason that this is important is because this
means that about half of the almonds from a tree that is not bitter will also produce
trees that are not bitter.  By contrast, almost all of the acorns from a "good" oak tree
would (if you plant them) produce an oak tree whose acorns are
bitter.

This means that it would be much easier to
selectively breed good almonds than it would be to breed good oaks.  Therefore, people
would quit trying to domesticate oaks but would continue to try to domesticate almonds
-- they would have a much better chance of success with the
almonds.