The implied subject of 'discounted'

The implied subject of 'discounted'

The passage below is from ‘the Blank Slate’ by Steven Pinker.

http://evolbiol.ru/blankslate/blankslate.htm

Hamilton had shown how a tendency to make sacrifices for relatives could have evolved. Relatives share genes, so any gene that nudges an organism to help a relative would be indirectly helping a copy of itself. The gene will proliferate if the cost incurred by the favor is less than the benefit conferred to the relative, discounted by the degree of relatedness (one-half for a full sibling or offspring, one-eighth for a first cousin, and so on).

I'd like to ask a question regarding the underlined 'discounted'.
The implied subject of 'discounted' seems to be 'the benefit' in a way, but I cannot rule out the possibility that it can be 'the gene'.

Let me out of this dilemma.

Regards.