High school biology is typically taught with an emphasis on human biology. The human body is broken down into distinct systems without regard to the origins of its parts. As a result, students are left with the impression that our biology is incredibly unique as opposed to a consequence of conservative replication and the retention of traits over millions of years. Here, I present a brief example of how the practice of phylogenetic systematics affects how we identify ourselves, and I pay homage to a particular section of our evolutionary legacy that joins all animals great and small with an interactive laboratory exercise.
Evolution educationThe diversity of lifeSystem evolutionPhylogenetic systematicsHomologyMonophyly
Within the confines of our insulated homes and stocked refrigerators, it is easy to understand how humans can feel disconnected from nature. There exists this sanitized notion that we have left that world behind and are now closer to the heavens than to earth. Beastly comparisons thus quickly offend our “higher” senses, except perhaps when honoring our physical and sexual prowess. It is no wonder then why humans have alternatively admired and loathed the “Great Ape.” Like looking into a mirror, we are drawn to the familiar and yet abhor the reflection starring back. Unsurprisingly, there were mixed reactions when New Zealand granted legal protection to “non-human hominids” in 1999 and after researchers declared that the two chimpanzee species should be included within the genus Homo because we share 99.4% of the same critical DNA sites (Connolly K April 1 2007; Sample I Janurary 24 2006). Animal lovers rejoiced, moralists stammered and ridiculed, while most scientists were oblivious to the one thing they all shared in common: they were all stuck with Linnaeus back in 1758.
Many are undoubtedly familiar with the use of Latin binomials (i.e., Panthera tigris) arranged into progressively higher orders of rank (i.e., species → genus → order → class → kingdom) in traditional scientific classification; it’s what we were taught in grade school and what we continue to teach. Unfortunately, we’re about 50 years or so behind the actual science (and those within the scientific community are far from exempt). Unbeknownst to most, when Swedish botanist Carolus Linnaeus devised the system that would become his namesake, it was more than just taxonomic housekeeping. Linnaeus fancied himself to be a “second Adam,” ordained by God to assign every plant, animal, and mineral its proper place in the natural order. In his own words, “God created, Linnaeus arranged.” It was during the tenth edition of his hailed Systema Naturae (1758) that Linnaeus blessed humanity with the species name sapiens and placed us in the genus Homo at the head of a revised table, the order Primates, meaning of “first rank” (Douthwaite 1995; O’Flaherty and Shapiro 2002). But we were not alone.
Undoubtedly influenced by the discovery and tales of anthropomorphic apes or orang outangs Moran 1993, Linnaeus divided the genus Homo into Men of Darkness (Homo nocturnus) or Troglodytes (“cave-dwelling men”) and Men of Light (Homo diurnus), which included Adamite men (Homo sapiens), monstrous men (Homo monstrous), and wild or “feral” men (Homo ferus; Douthwaite 1995, 1997). Over time, both legend and actual specimens intertwined, and when the dust settled, the common chimpanzee, or Troglodyte, was kicked out of the genus Homo and placed in the genus Pan (Oken 1816). Now to the casual observer, this might seem rather trivial, but the move signified more than just a taxonomic reshuffling; it removed the beast from the hallowed chambers of man and fully projected the element of the demonic upon the innocent ape through the intersection of humanity, darkness, and unbridled sexuality (the horns, hooves, and phallus of the Greek satyrs and god Pan meets the Christian Satan). The bonobo, Pan paniscus (Schwarz 1929), far more deserving of the fun-loving satyr imagery, would soon join its cousin, Pan troglodytes, in purgatory (Fig. 1).
As it is difficult to show the blood relationship between the numerous kindred of any ancient and noble family even by the aid of genealogical trees, and almost impossible to do so without this aid, we can understand the extraordinary difficulty which naturalists have experienced in describing, without the aid of a diagram, the various affinities which they perceive between the living and extinct members of the same great natural class. (Darwin 1872)
Appeals to authority and subjective notions of similarity—fundamentally no different than the “yardstick” applied by geneticists spouting percent differences—formed the basis of taxonomic practice well into the twentieth century. Darwin’s vision of a taxonomy that actually reflected a “community of descent,” or genealogy, would have to wait until German entomologist Willi Hennig laid out the groundwork for what we now call Phylogenetic Systematics, or Cladistics. In a nutshell, phylogenetics is the scientific discipline of classifying organisms based on evidence of similarity due to common ancestry (homology). More precisely, this comes in the form of shared, special homologies or synapomorphies. For example, among Amphibia, Mammalia, and Reptilia (including birds), Mammalia and Reptilia are considered more closely related because they share a number of synapomorphies thought to have originated in their common ancestor, such as the amniotic egg.
Brevity prevents me from going into more detail (see reference Brooks and McLennan 2002 for a detailed description of the phylogenetic method), but the purpose of phylogenetics is the discovery of monophyletic groups, which are natural assemblages that contain an ancestral species and all of its descendants. The members within a monophyletic group share a unique set of relationships compared to species placed outside the group (Wiley et al. 1991). Only species (unique lineages or branches) and monophyletic groups are considered to be natural taxa because they exist in nature as a result of evolution, or “descent with modification.” In this sense, Linnaean ranks are obsolete because the same organisms would exist in a group whether you called it a class, an order, or a family. Below is an example of a phylogeny with several monophyletic groups identified by a simplified set of easily recognizable synapomorphies (Fig. 2).
Why is this relevant to you as secondary school teachers? The feeling of disconnect described during the outset is something quite palpable in our approach to teaching the biological sciences. Too often we portray the human body as some kind of independent wonder instead of paying homage to it as a wondrous product of natural history. We describe and often teach the strands of biology as disjointed units when we have a real opportunity to portray it as a cohesive discipline by building around an evolutionary framework. This will prove to be even more important as the Internet Age continues to provide us with access to an incredible amount of information while pushing us to the very limits of filtration for meaning. Biology, and science in general, will need clear, robust foundations from whence new information can flow and return, and there is no reason why biology cannot be taught as a unified macroevolution course, particularly at the senior level.
Beyond the level of species, much of the name game is indeed semantic. Whether there is greater value in keeping Pan to specifically identify the monophyletic group of common chimpanzees and bonobos rather than absorbing it within Homo really depends on whether you’re a “lumper”—prefer to name just a few monophyletic groups with lots of species in each—or a “splitter”—prefer to name a lot of groups to emphasize diverse relationships. But never forget that you are more than just Homo sapiens: You are also a Craniate, a Vertebrate, a Gnathostome, a Bony Fish, a Lobe-finned Fish, a Tetrapod, an Amniote, a Mammal, a Placental Mammal, a Primate, an Old World Monkey, and even a Great Ape, which would be an unnatural grouping without our inclusion, just to name a few. We have a lifetime membership in a shared history that stretches all the way back to the first cell. And just for clarification, since evolution is “descent with modification,” you are not a hagfish (Myxiniformes) or a ray-finned fish (Actinopterygii) unless you happen to sport slime glands and ganoine scales, respectively. I’m sure that’ll both spark curiosity and offend in more ways than the self-conscious ape in the mirror. “A rose by any other name would smell as sweet…”
Bart: Not if you called ‘em stenchblossoms
Homer: Or crapweeds.
Marge: I’d sure hate to get a dozen crapweeds for Valentine’s Day. I’d rather have candy.
Homer: Not if they were called scumdrops (“The Principal and the Pauper,” The Simpsons 1997)
, Toronto, Canada
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