The semantic subject of ‘warping or defacing’

the semantic subject of ‘warping or defacing’

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

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

And so a gene that disrupts a mental ability need not be a defective version of a gene that is “for” that ability. It may produce a toxin that interferes with normal brain development, or it may leave a chink in the immune system that allows a pathogen to infect the brain, or it may make the person look stupid or sinister and thereby affect how other people react to him. In the past, geneticists couldn't rule out the boring possibilities (the ones that don't involve brain function directly), and skeptics intimated that all genetic effects might be boring, merely warping or defacing a blank slate rather than being an ineffective version of a gene that helps to give structure to a complex brain. But increasingly researchers are able to tie genes to the brain.

In this passage I’m not sure about the semantic subject of ‘warping or defacing.’
In a way it seems ‘skeptics,’ but in another I cannot rule out the possibility of ‘all genetic effects.’
Now I am leaning toward ‘all genetic effects’ but still hesitant to come to a conclusion.
I’m in a dilemma.

Thanks in advance.

Regards.