Whether the acts were intentional or unintentional can never be known, but it has been understood by a team of archaeologists that early man harmed and altered the environment.
For example, aboriginal people in Australia burned huge areas to change the landscape so they could hunt animals more easily.
Perhaps the most famous example is the way mastodons and giant sloth and other ice-age animals were killed off by roving bands of hungry humans.
He said that he's discovered that indigenous people even altered America's coastlines, thousands of years ago.
Rick has evidence in the form of 6,500 years old palm-sized shells, which were dumped by people living on the islands of California, after they ate the red abalones and, unknowingly, became "dune-builders."
"So there might have been a five-foot dune there at one time right above the beach and a group of hunter-gatherers came in, lived on top of that dune, dumped their refuse there and left. And this creates a pavement there that anchors that sand," he said.
Small dunes eventually became big ones, built up like a layer cake, with trash dividing each layer.
Then there were intentional changes that people wrought, like the clam gardens of the Pacific Northwest.
People built rock walls into the ocean shallows.
"What these rock walls do is they create behind them an area of sandy substrate that's really good for clams. You can kind of think of them like a terraced garden," said Rick.
Rick has also found layers of sea otter bones thousands of years old in California's Channel Islands.
The layers above just had sea urchin remains. According to Rick, people killed the otters because they ate too many shellfish.
Since otters also prey on sea urchins, the urchin population exploded. All those urchins ate up the kelp forests, creating what Rick calls an "urchin barren."
Rick said that intentionally or not, hunter-gatherers altered the environment for a long, long time, long before agriculture emerged.
"The take-home point to some extent is that humans do things to make their life easier," said University of Nebraska anthropologist Raymond Hames.
"It was really hard to make a living back then, so you know, you took advantage of the knowledge and skills you had in order to make the environment useful to you," he added.