"Traffic must have grown sparse, or we'd not see random variations."

Without a genetic control, any differences you see may be due to random variation in people's brains.

Smart showed by using physical characteristics that the species were separate and not a result of random variation.

It's no longer a question of the usual random variations in the census numbers.

"I have been attempting to do so, but the random variations make it impossible."

He might be trying random variations to see what works, but I doubt it.

They are able to produce random variations, which are new.

They represent the average, expected behavior of a system, but lack random variation.

However, many of them show random variations in brightness lasting only a few months or, on occasion, days.

It's just part of the random variation in the world.