I have a feeling that people's intellectual abilities and intellectual progress are mainly affected by their environment - Phizzy
The evidence from twin studies show that our intellectual capacity is predominately nature rather than nurture.
Of course it almost goes without saying that a genetically gifted child needs the opportunity to realise their potential.
For details see 'The Blank Slate' by Pinker and 'Nature Via Nurture' by Matt Ridley.
LUHE - I agree. I assume you didn't so much mean diversity in intellectual ability but in opinions and perspectives? Jonathan Haidt has written about this. He started a project called the Heterodox Academy to encourage diversity among university academics.