There was no concept of biological species before the late 17th century in natural history. So why did we get a concept of species in the first place? What is “species” needed for?
The answer is that the reason we have a notion of species in biology at all is because of Noah’s Ark. Seriously.
The word “species”, as John Locke noted, is just a Latin word that means a kind or sort of things. In late Latin, after the renaissance, there were two words that meant “a kind”: genus and species. As far back as the Greeks, the equivalent terms in Greek–genos and eidos–were used interchangeably.
What is ironic is that in Aristotle’s influential system of logic, and in Europe up until the late 17th century, genus was the more general kind (general being the adjective of genus) and species was more special (special being the adjective of species). So when Aristotle or his students did natural history none used these terms in the logical way. Likewise, in early modern taxonomy, they aren’t used as they would be in logic.
So what is at issue is not that scholars of the time talked about kinds of species. Botanists had spoken of species since botany properly began in the 16th century. Zoologists had also done so in the same period.
The issue is why there had to be a particular basic rank that species occupied in the living world. Before this, there was no such rank, no special basic kind in natural history.
Why did we think there were most basic kinds of organisms? It was a theological problem. The trend towards literalism in biblical interpretation after the Reformation, and the rapidly increasing number of species described by European naturalists as the Americas and the Orient were explored, raised an urgent question. Could the story of Noah’s Ark be true?
Johannes Buteo (1492-1572) started a tradition of literal interpretations of the Ark, and later authors worked off his Arca Noe, published in 1554. Bishop John Wilkins (no close relation) noted that Buteo included several fabulous creatures on the Ark. Buteo’s term for kinds was genus.
A German-born Jesuit, Father Athanasius Kircher (1602–1680), working out of Rome but in correspondence with explorers and scholars around the known world, attempted to provide a “scientific” solution to Buteo’s problem. (I put scientific in quotes because it is an anachronism: there was no distinction to be had between theology and science in the 16th century, or for some time to come. This does not imply somehow that science and religion were in conflict here.)
Kircher is doing what any good naturalist would do – utilise all lines of admissible evidence, including, at the time, the Bible. He tried to work out how many of each kind would fit on the Ark, and so he had to determine what the basic kinds were. He didn’t give them a special name, though; he just used that ordinary word species.
A little before Kircher, my namesake Bishop Wilkins (1614-1672) published his Essay Towards a Real Character and a Philosophical Language. In it he tried to capture all facts about the world in a universal system. While Wilkins used genus and species in the usual logical way, he also sought to establish what species could fit on the Ark. Wilkins gave a table:
In it he noted that the Mule was not a true species, because it is “a mungrel production” (a hybrid). Likewise various kinds of cattle (“Beeves”) and sheep are mere varieties of the original species.
Wilkins employed the young John Ray, a botanist and his zoologist patron Francis Willughby, to draw up the lists of species used in the Essay. Ray and Willughby (who died unfortunately young) were gently mocked by their peers for the artificiality of Wilkins’s system. Stung, Ray began to do the hard work of classifying plants by observation. So he needed to define species:
In order that an inventory of plants may be begun and a classification (divisio) of them correctly established, we must try to discover criteria of some sort for distinguishing what are called “species”. After long and considerable investigation, no surer criterion for determining species has occurred to me than the distinguishing features that perpetuate themselves in propagation from seed.
The bit I’ve put in bold was the first definition of these fundamental units of natural history. In modern terms, it was the first biological notion of species.
Why did natural history need units? After all, people had been identifying kinds in botany and other areas of natural history for a great many years, and some of the species of plants identified in the century before this definition are still held to be “good” species. The only answer I can find is that species were required by theology, defined using philosophical distinctions.
And one has to wonder if, as a rank, species are still statements of faith, in conservation, genetics and taxonomy in general. Ironically, measuring diversity using evolutionary relationships of species for conservation is called the “Noah’s Ark Problem”. But while individual species do seem occasionally to be real objects, a good many aren’t - they can be split into smaller groups or lumped into larger groups.
Some biologists, like Brent Mishler of the University of California Berkeley, consequently deny the existence of species. Like him, I deny their rank. There is no “unit” of evolution or rank in biology. But I believe there is a reality to the phenomenon of species: we really do see patterns in groups of organisms that we name species. The mistake arises in thinking that our perceptions somehow give us the structure of the world. Sometimes they do, sometimes they don’t, and species can only be resolved by finding the actual structure of the biological realm.