33Earthly creators of painting, literature and poetry often reveal their state of mind in their creations, so he wanted to apply that principle to understanding the deity. Studying God's creations would reveal the mind of the Creator. Apparently, he did not consider the possibility of more than one such creative personality. The idea of multiple creators had pretty well died with the ancient Greeks, and monotheism, it seems, was critical to the rise of science. But that is a story for another time. Certainly, it was critical for Linnaeus.

But beyond the basics, things really got dicey. As Linnaeus's fame and grand idea grew, people decided that his "species" must be the "kinds" of Genesis, therefore fixed and unchangeable. Linnaeus inspired his disciples and students to take long voyages and expeditions searching for new forms of life. About a third of them lost their lives in the process. These were dangerous days.

But the specimens brought to Linnaeus from these broad-ranging trips led to great difficulty. Whereas he had originally named, say, two different plants as different species, now he was being presented with specimens whose appearances ranged progressively from one to the other. Was he dealing with one very variable species, or with many species? His grand idea was in trouble.

The basic problem was that he was using the criterion of physical shape or form to define a species. One particular organism was a different species from another one if it looked different. But how different? Were the variations in the sexual structures the critical criterion, or should variations in other body parts (leaves, stems, flowers) be considered as well?

We still have to depend on this "morphological definition" when dealing with fossils, and just do the best we can. But with living species other definitions have been developed, some two dozen of them. The most popular is that of reproductive isolation: A species is a group that is naturally fertile among itself but that is "unable" to reproduce with other, morphologically similar, groups. So horses and donkeys are considered separate species because, though they can produce very vigorous and viable offspring (mules), those hybrids are, themselves, generally sterile. Because there is no genetic exchange between horses and donkeys, we consider them separate species. But this definition, too, has huge problems. Let's take an example to get ourselves into the local scene.

Lewis and Clark, more than 200 years ago, encountered a shrubby bush in South Dakota. It was eventually named Atriplex canescens, the four-wing saltbush. These days, we use it for reclamation of tailings of mining activity, for reclamation of over-grazed ranges, for re-planting after fires, and as a plant for nutrient-poor soils. It grows natively from the southern-prairie provinces of Canada all through the western United States and into Mexico. But it also is highly variable, and we'll explore that and the work of some of our local botanists next time.