Ever worried about nature versus nature? Fret no more. Garry's on it.
Precisely what Garry thinks is meant by "proving", we are not told, nor do we get to find out which studies achieved this proof. Still, for all I know, the relevant information is all in Garry's book:
regrettably I have inherited an insufficient degree of work ethic and can't be arsed to find out for myself.
Would it be worth it? This isn't Garry's first foray into the world of studies and what they prove.
How did that one go?
Or this one (thanks to Jonathan for reminding me).