In your excerpt of "Intelligence: Is it the epidemiologists' elusive 'fundamental cause' of social class inequalities in health?":

As environments get better, genetics explain more of variance; as societies become more meritocratic, they become more unequal.

IOW, as environments get better, they become more uniform (in their effect). Is this saying that environments contribute mostly negative factors, not positive ones, to development, so the best environments affect outcomes least? And if so, how well established is it?