I stumbled over the same quote. What "gift"? From whom? What "responsibility"? And just how is being "lucky" at odds with being "superior"?

To see the nonsense, let me paraphrase:

"Because giftedness is not to be talked about, no one tells human children explicitly, forcefully and repeatedly that their intellectual talent is a gift. That they are not superior animals, but lucky ones. That the gift brings with it obligations to other animals on Earth to be worthy of it."

The few people who honestly believe that are called a lunatic fringe. And yet, it is the same statement as Murray's, merely in a wider context.