In any control system that is functioning properly, the methods used to control a signal won’t be correlated with the signal they’re controlling.
Worse, there will be several variables that DO show relationships, and may give the wrong impression. You’re looking at variables A, B, C, and D. You see that when A goes up, so does B. When A goes down, C goes up. D never changes and isn’t related to anything else — must not be important, certainly not related to the rest of the system. But of course, A is the angle of the road, B is the gas pedal, C is the brake pedal, and D is the speed of the car.
In the past, GDP and resources use have always been tightly correlated. But this is just drawing a line through some data — it’s not based on any deep theory. And in fact, these correlations can change very quickly. Just as one example, here’s energy use versus GDP since 1949.
If you were sitting in 1970, you could look at this curve and claim, very confidently, that economic growth requires concomitant increases in energy use. And you’d be wrong. Because the trend is your friend til the bend at the end.
Drawing requires that you pay attention to every detail—even the seemingly unimportant ones. In creating an image (no matter how skillfully), the lines and tones on the paper provide ongoing feedback as to what you have observed closely and what you have not.
Scientific illustrations can achieve certain things that photographs cannot. A good illustration can portray difficult-to-photograph or rarely witnessed events. It can incorporate everything that’s important into one single image or show a special view of a subject.
It would be next to impossible to observe, in nature, a dozen different aquatic species in their natural habitat, posing perfectly together and all in focus at one time—but such a scene can easily come to life in an illustration.
My studies of live animals usually begin with a series of quick drawings, all on a single page. When the subject changes position—which it pretty much always does—I abandon the first sketch and start a new one. Continuing on in this way, the page fills with mostly unfinished squiggles until the animal eventually resumes one of its earlier poses. If that happens, I add as much detail or refinement to one of the easier sketches as I can. While this is all going on, I also jot down written notes that help explain what I observed and what seemed significant.
In-person, live observation of color is a practice for which I feel there is no adequate substitute. Photographs are often imprecise in reproducing color.
Colors in nature are, in general, more subdued than what comes directly from the pencil or the tube of paint. Greens, especially, tend to be a lot browner than we expect.
Leave the drawing unfinished. Record as much information as you need, but don’t draw any forms, details, or colors that are merely repetitive. The back and front of a representative flower on a plant, for example, or half of a bilaterally symmetrical animal may be all that’s necessary.