When we think about the loss of biodiversity, it evokes the idea of loss of variety, the loss of a diversity of creatures that, in essence, share a number of common traits. They have the same genus, and from that, they specialized, adapted, and spread out into their environments.
Here's some evidence that we've suffered catastrophic losses in debate biodiversity (assuming you are with me in the idea of an equivalent sense of biodiversity for intellectual practices). This chart, taken from Nichols & Baccus's 1936 volume, Modern Debating, hoped to guide the reader through the dizzying array of different events that would be called debate. For students in the early 20th century, debate could take on many forms, and these forms could all co-exist.
Today what do we have? We seem to have a number of forms, but our entire tree is structured from the roots of the tournament. CX, LD, PF, CEDA, NDT, NPDA, NPTE, APDA, EUDC, North-Ams, BP, CUSID BP Nats, USU, WUDC. All acronyms, save one, and all derived from types of debating done for one purpose - tournament style contests.
Take a look at the variety on the above chart and think - if such a chart were made today, there would only be one line - the argumentation line - and on it would be all the competitive formats. The persuasive line - where debaters reached out in a competitive sense to broader audiences - has evaporated.
The division the authors make is interesting to say the least - argumentative forms are more competitive forms: These are the types of debate that focus on competition the way we understand it today. Persuasive forms are more general: They can be competitive or not - really depends on the audience.
Perhaps the division is one of audience. Persuasive forms focus on an audience with a high concentration of members of the public. Argumentative forms focus on an audience that has little to no public. However in 1936 it is hard to imagine a debate contest that wouldn't draw community interest. Today we don't have to expend any effort to imagine that.
Today's chart would be one line. Purely argumentative. We don't even bother teaching debate students anything from the persuasion line. In fact, recent attempts to help debate pedagogically, such as the Guide to Debate produced before WUDC Malaysia, attempt to flatten the distinction: What is argumentative is persuasive, and vice versa. Why keep the distinction when the people watching and evaluating your debates are so homogeneous that the consideration of variance in how they hear you has been eliminated with a joyful medical precision?
Most current collegiate debaters would see the loss of the persuasive line as no big loss at all. Those are side projects to the "real" work of debating. Others would say the distinction is false: Contemporary debate focuses on persuasion. I wonder. What would be needed, and what would be the value, to teach all these forms in a contemporary debate program? The monopoly of tournament contest ideology is a difficult regime to break. Returning to history might be a good way to show the impermanence and newness of the "tournament as debate" model of debate instruction that is thoughtlessly reproduced pedagogically across the world.