Evidence and Motive: Anna's Hummingbird and Loretta's knife

As comparative biologists we are limited in our knowledge of the natural world. We know for instance that some groups are natural and that they share closer relationships with each other than they do to other groups. We also know that some taxa belong to certain groups while others do not. Take the case of Anna's hummingbird (Calypte anna). It is a taxa that belongs to a monophyletic group called birds. We discover that Anna's hummingbird shares closer relationships with other birds than it does to say mammals. As a systematist relationships are all we know of the phylogeny of Anna's hummingbird.

Knowing a relationship doesn't seem to grab the attention of the general public, students or granting bodies as much as evolutionary mechanisms do. What if we proposed that Anna's hummingbird originated in Madagascar and generated a plausible rational argument to support that hypothesis? Suddenly we stir some interest within the biogeographic and marco-ecology communities. When we propose that hummingbirds and birds as a whole are not only related to therapods, but are also their descendants, do we really get everyone excited. But what happens when we reverse the situation - swap our knowledge of hummingbird relationships as explanatory hypotheses and explanatory hypotheses as knowledge? Ebach & Williams (2004) proposed a thinking exercise that is analogous to the suggested proposition above.

Loretta the Murderess

A hypothetical group of detectives kick down a locked door. Behind it stands a woman who answers to the name of Loretta. Next to her on the floor lies a man with a knife in his back. All three objects are covered in blood, which upon further investigation turns out to belong to the deceased. For added effect, the knife has the word "Loretta" inscribed on it in black ink. How do we interpret the scene?

As the title suggests we may call it a "murder", and "a horrible accident", or even "an act of self defense". Whatever the motive is, what is unmistakable is that the locked room contains a woman (Loretta), a man (deceased) and a knife (inscribed with the name "Loretta"). Since no one outside the room witness any action or event, all motives are suspended. All we know are the existence of these three objects.

Let us say that, for some unexplainable reason, the scene is no longer investigated and, for the sake of this argument, all information relating to the Man, the knife and Loretta vanishes. We are left are a series of conflicting motives (i.e., vengeance vs. victimization) and morals (i.e., justice vs. injustice) that all are supported by that same evidence. Now for the analogy - what would happen if we were to swap the evidence for motive and the motive for evidence?

Depending on which way you argue the "evidence" (read "motive") Loretta's innocence is based on the best argument based on the "motive" (read "evidence"). We may propose two explanations to defend or accuse Loretta, namely the "extremely vengeful person" hypothesis and the "victimized person" theory. Each of these totally conflicting theories however based on the same "motive" (read "evidence") - a knife, a dead man and Loretta covered in blood all located in a single locked room. Given that this is all that there is in terms of real evidence, any hypothesis can be made to fit based on nothing more than rhetoric.

Thankfully we no longer live in a society where motives are considered to be evidence (e.g., witch-hunts and other heresies). We do however live in a society that does treat its subjective mechanisms as evidence and its evidence as explanation.

There would be many people who would support the following argument below:

"Birds have evolved from Dinosaurs"

or

"The center of origin for hominids is Africa"

Let us take the first argument. The motive or explanation has been replaced as "evidence". Birds have not evolved from Dinosaurs because "Dinosuars" do not exist as an evolutionary group, that is a monophyletic or natural group. The Dinosauria as a non-monophyletic group is real evidence. The argument that Dinosaurs evolved into birds is by far a more exciting prospect. In doing so however we disregard the evidence to hand - namely that Dinosaurs are a non-evolutionary grouping. The second argument is similar.

We as outside observers have never seen Loretta place the knife into the man, we assume she did because it is her knife and the room was locked. Guilt by association is a terrible tragedy when it occurs in our legal system, but the practice is encouraged in systematics and biogeography. The oldest hominid remains are found in Africa, therefore it is assumed that this is where the group originated from. Guilt by association is not empirical or scientific in anyway as it is based mere speculation, namely what may or may not be there. Additionally no one has seen hominids originate in Africa, so the whole argument is superfluous and speculative, every much like the motive (if any) in the Loretta example. If an older hominid bone is found elsewhere, say Antarctica, the hypothesis will change, but be based on motive rather than on evidence. Systematics and biogeography may appear to become more interesting the more non-empirical hypotheses we spout, but by no means do we become more knowledgeable.

References
Ebach, M.C. & Williams, D.M. (2004). Classification. Taxon 53: 791-794.