“In the last two or three decades, historians have found it hard to think across large time spans,” he contends; gone are the sweeping narratives of humanity’s advance. The antidote to this “shallow history,” he said, is “deep history,” stretching back 50,000, 500,000, even 2.6 million years to the earliest humans.

There is no need to put the whole paragraph in italics.

Unless it were a bloody murderer, / Or foul felonious thief that fleeced poor passengers, / I never gave them condign punishment:

[…] she glanced about her in an imperious, challenging sort of way, with looks and gestures that clearly were unstudied.