Inheritance - Edit

[Brownlie]

Inheritance

When he was five, young Gerald’s father spanked -- Do you need "young"? Doesn't the previous clause explain the youth? Also not sure about this enjambment. Seems like spank is the surprise word, not him. Would spank be better on the next line?
him angrily for playing near the edge, - near the edge of what?
tormenting animals, and most of all -- Would you put a comma after all? Not sure how grammatical you want to be. 
for toying with himself.  Young Gerald learned -- The enjambment in this line to "toying with himself" is better. It's both surprising and cruel.
what things were right and wrong, and soon forgot -- What things were right and wrong seems a bit wordy. Morality, right from wrong, righteousness or what's wrong. Many ways to reduce word count. If padded, probably more meaningful things can be added. Not sure if implied subject warrants FANBOYS comma.
those loving pains and terrors that had taught
him which was which.  At thirty-three his shrink -- My initial reaction is to cringe from "which was which" because it seems like compounding sloppy references (what's which referring to) with sloppy redundancy (two which). That being said, there seems to be some good psychological stuff/pause to think about words going on. 
recovered memories that showed his angst was caused
by rage and anger, violent abuse -- Rage and anger seems redundant. 
his father had inflicted on a son
he hated.  Gerald took it all to heart -- All seems unnecessary here. 
and never punished his son Ted except
with smiling time-outs.  No-one could explain -- As far as I know, the dash is normally for adjectives. No one is a noun here. 
why Ted turned out sadistic and depraved,
thrill-seeking and amoral - unafraid
of playing near the edge.  Old Gerald thought
this vicious streak must be inherited: -- was instead of must be? still stuck with to be verbs though.
Ted’s grandfather, he told himself, was mad. -- Good ending, but does thought mean told himself in only one word?

When he was five young Gerald’s father spanked
him angrily for playing near the edge,
tormenting animals, and most of all
for toying with himself.  Young Gerald learned
what things were right and wrong, and soon forgot
those loving pains and terrors that had taught
him which was which.  At thirty-three his shrink
informed him that his fear of heights was caused
by rage and anger, violent abuse
his father had inflicted on a son
he hated.  Gerald took it all to heart
and never punished his son Ted except
with smiling time-outs.  No-one could explain
why Ted turned out sadistic and depraved,
thrill-seeking and amoral - unafraid
of playing near the edge.  Old Gerald thought
it had to be inherited somehow -
Ted’s grandfather, as he recalled, was bad.

A little blank verse - have to get a bit of strikebreaking in before the "Poets' Strike" is over!

Content seems pretty cool, which is the hardest part IMO. Critique is mainly about style, with padding and stuff. Good luck with it.