I would argue first that humans are a part of nature, not apart from it. So, what we do is, in a sense “natural”. Many species of animal modify their environment to make it more to the animals desires. That said, the thing humans do, much better than any other animal we are aware of, is the control and application of energy. Many animals will pick up a rock and use that rock to bash stuff. Some animals may also pick up a rock with a particularly sharp edge or pointy bit and use that edge/point to crack open shells or husks. Hominids (not just modern humans) took that one step further and began preferentially picking out rocks which formed especially sharp or hard points and applying energy to that rock to form useful points. Once early hominids made that discovery, Oldowan tools proliferated in manufacture and use.

That manufacture and use was the advancement which set hominids apart from other animals. And, hominids also show signs of making choices which require planning ahead in rather abstract ways. To step back for a moment, Oldowan tools could be argued as hominids just following what they say happen “naturally” (without the directed energy usage of the hominid). One rock falls on another rock, and it breaks into a nice, pointy rock. Hominid see, hominid do. And we get hominids banging rocks together to make pointy rocks. But, then it goes further than that. Hominids start planning how to bang rocks together, spending time and more importantly energy, banging on a core to prepare it for a later strike, which will break off a flake with a fairly specific shape. The shaping of later stone tools likely involved the creation of tools (stone and organic) to manufacture the stone tools the hominids planned to use. Hominids at this point were planning multiple steps ahead in the process and expending energy to that goal.

This is where, I think, the idea of the application of energy really comes in. Consider what an early hominid would have to think about to produce something like an Acheulean tool. First off, they need to select a core, a large rock which may not be somewhere the early hominid would be able to safely sit and work it. So, they have to select a rock and carry it back “home”. This takes time and energy which is not being put to direct use in survival. It also exposes the hominid to danger, as carrying a large rock likely took both hands and may have been awkward. Once the hominid gets the rock home, they then sit and spend time and energy dressing the core. Breaking off bits which may not be as useful (waste flakes are a common byproduct of stone tool manufacture). Again, this is time and energy directed at a task which is not immediately useful, but shows planning several steps ahead. Finally, the hominid begins shaping the final flake they plan to remove. At this point, the tool maker must have a good understanding of how the rock is going to fracture. There has been a very deliberate, very well planned application of a lot of energy to get the rock ready for the final strike to break the flake off. All of that energy has been expended to a single goal of making that tool.

Granted, even this definition of “natural” has a gray area. Beavers direct a lot of energy making dams. But, I’d argue that they do not require the same level of foresight and planning. The “planning” for the damn doesn’t rise much above the level of random chance. Beavers use logs and sticks which are already there, with the more advanced action being the cutting of trees for use in the damn. But, they are not going tens of miles to select specific tress, it’s more a haphazard, “tree here, tree gets used”. Similarly, birds grab twigs and anything else of roughly the right shape to build their nests. And those dams and nests have a pretty direct application to survival. A rock which needs to be shaped before a flake can be broken off has a much less direct application to survival.

So, it’s a bit of as sliding scale, with a lot of things humans do being more “natural” and some things animals do being less “natural”. If I grab a fruit and eat it, that’s pretty “natural”. I’m directing energy to do something directly involved in energy. If I pick a fruit from a tree, put that fruit in a box, put that box in a boat and transport that box to the other side of the planet, so that I can receive a stack of bits of paper, that’s a lot less “natural”.