EVOLUTION
    By the 18th and 19th centuries, zoologists were beginning to draw conclusions (or at least ask better questions) about life's origins.  As European scholars set out to systematically catalogue natural world, they began to notice patterns.  Elephants in Africa bore a striking resemblance to those in India, but kangaroos in Australia looked like nothing, at all.  Just as humans had bred different kinds of dogs, it seemed that some process was at work, making different breeds of everything else.  For most of history, scholars, if they gave the matter any thought, followed Plato in assuming that modern breeds of organisms were corrupted descendants of perfect archetypes.  Later biologists (most notably Jean de Monet, the Chevalier de Lamarck) theorized that an organism's environment communicated changes that it could pass on to the next generation.  We are all familiar with the example of the giraffes stretching their necks and the smith's strong right arm being passed to his son, but these early evolutionary hypotheses do have some merit.  The Platonic ideal of corrupted archytypes (if one strips away the moral connotations) are strikingly similar to Darwinian theory (which I will get to in a minute) and Lamarckian evolution, long considered completely wrong-headed, has now been revealed as a valid method of biological change, at least in some cases.  Modern evolutionary theory, however, is most emphatically not Lamarckian or Platonic, but Darwinian.

    Charles Darwin was (by a very short margin) the first person to publish a description of natural selection.  Natural selection is nothing more than the automatic version of the selective breeding that humans have practiced for thousands of years, and is probably the most basic mechanism by which species change over time.

    Very briefly, Darwinian evolution functions by killing every member of a population that does not conform to certain standards.  That is, those that cannot survive do not.  Whether by accident or design, genetic variation enters the system, and one organism ends up a little different from another.  Some variations are beneficial, increasing the organism's chances of reproduction, others are neutral, and some are detrimental, making the organism less likely to breed (by, for instance, killing it).  Those organisms that do survive will hopefully breed, and pass on whatever trait kept them alive. Straightforward Darwinian evolution is very slow, with beneficial mutations building up over the eons and, little by little, creating a new species.  Evolution by natural selection is simple, but the process is subject to much elaboration.

    Sometimes evolution is neither simple nor slow.  If, for instance, two populations of the same species are isolated so individuals of the two populations can no longer interbreed, they will begin to build up distinct mutations.  These mutations may not be particularly beneficial—two spots on the wings rather than three, or blue eyes instead of green eyes—but enough of them will make the two populations so different from each other that they become different species.  Even if the barrier between the two populations were removed, they would be unable to interbreed.

    Another interesting twist on classical Darwinian theory is that genetic variation need not be expressed as a change in the organism's form.  Most of our DNA is not used at all, and functions as a source of backup variety to be used when the right circumstances present themselves.  If an ecological catastrophe wipes out a number of organisms, the remaining species go through a process of radiation and diversify with dazzling speed.  The cichlids of Africa's lake Victoria, for instance, could not have been living there more than 750,000 years (the lake, itself is at most that old), but in this eyeblink of time, they have radiated into an array of species to cover almost every lifestyle a fish could have.  Genetic tests conducted by Axel Meyer et al. indicate these different cichlids species actually contain less genetic variety than the single species of Homo sapiens.  The difference between us and the fish is that while most humans' genetic variation is latent, the cichlids have expressed their genetic diversity physically.

    There are only so many different environments on Earth, and as species adapt to their surroundings, the same adaptations are re-invented again and again.  Convergent evolution occurs when two species of wholly different lineage share an outward appearance molded by their environment.  Spec abounds with examples of convergence (as does Home-Earth), some of which include the twitiavians  mistriders  versus the neognath swoops or the North American nodopotami  versus the Eurasian potamoceratopses.  In both these cases and many others, the outward form of two organisms are similar even though they are not related.  The only way to sort through convergences is to examine those parts of the organisms' anatomies that not subject to the selective pressures of their environments or cannot be changed if they are.  A mistrider, for instance, though it may look like a swift, possesses the bizarre palette configuration of a twitiavian.  The fact that the mistriders look nothing at all like other twitiavians is due to divergent evolution , where a different style of life has lead to a different body type from its ancestors.

    Another form evolutionary change, neither divergent nor exactly convergent, is parallel evolution, observed where Spec-world taxa have evolved in parallel with their counterparts Arel counterparts.  Most high-level taxa are parallel (that is, phylum Chordata exists both on the Spec-world and Home-Earth), but there are a surprising number of genus and even species-level examples of parallelism.

    Evolution as a concept may be simple, but the tremendous diversity of life both on Spec and Home-Earth is testament to the complexity the underlies natural-selections elegance.  Species drift apart, radiate, diverge, converge, and generally make the process of tracing back their lineages that much harder.

CLASSIFICATION
    Life has been evolving for almost as long as the Earth has been solid (some three billion years) and, evolution being a build-up of many small changes, some organisms are quite different from others.  Other organisms, however, are more similar, and some are quite similar.  Logically, those organisms most like each other are the most closely related, having had less time to develop distinction.  This argument, in a nutshell, is what cladistic taxonomy is all about.

    Cladistics (from Greek klados, twig) classifies organisms by arranging them into branching trees, where the most closely related species are physically closest together.  Cladistics traces its own ancestry back to the system devised by Carl von Linné (Carolus Linnaeus)  in the 1700s.  Linnaean classification was mostly concerned with naming organisms and placing them in hierarchies based upon their similarities.  The greater hmungos of the North American plains, for instance constitute a species, a community of animals that can interbreed to produce offspring with can then breed, themselves.  This species belongs to a larger (and somewhat arbitrary) grouping, a genus of other animals which are very much like the greater hmungo but cannot breed with this species.  These two names, genus and species, form the Linnaean name of an organism.  Linnaean names are usually Greek or Latin (though not always) and are written in italics, with the first letter of the generic name capitalized.  Thus, the Linnaean name of the greater hmungo is Megahadrus titanus.  Species borders are sometimes fuzzy, but in general, every M. titanus is genetically compatible with every other M. titanus, but not with any other organism, though those of genus Megahadrus (the sludger or Megahadrus potamus, for instance) may look similar.  Linnaeus created a system whereby every organism on Earth was designated by a pair of names, generic and specific.  No two species have the same Linnaean name; there are elaborate rules set up to ensure that no such confusion may occur.

    Linnaeus invented more than the idea of the species however, he also set up a complex hierarchy into which species could be placed.  The greater hmungo belongs to the species Megahadrus titanus, the genus Megahadrus, the family Hadrosauroidae, the order Ornithischia, class Reptilia, phylum Chordata, kingdom Animalia, and domain Eucarya.  Each of these groupings—taxa (singular taxon)—are based upon one or more specific characteristics (traits) that all species within the taxa share with each other and not with any other organisms.  For instance, Linnaeus grouped all creatures with feathers into class Aves and all creatures with hair and nipples into class Mammalia.  If the Swedish biologist had lived in Spec, where feathered dinosaurs and hairy, nipple-less multituberculates  are common, he would probably have drawn his classifications differently, but that is beside the point.

    Logical as it is, there are problems, with the Linnaen system.  Most fundamental is the fact that by Carl von Linné  was born before Charles Darwin  published The Origin of Species and introduced the world to the concept of evolution through natural selection.  Linnaeus used Plato's method to explain the resemblance of some organisms to others, and said that modern creatures were the corrupt descendants of a set of perfect archetypes.  Darwin, took this idea even further in saying that all life on Earth is descended from a single species.  Now, the purely arbitrary hierarchies of Linnaeus could be viewed as actual family trees, describing evolutionary changes through time.  How, though, can one describe the infinitely subtle variations of groups of species with just the few arbitrary hierarchies set up by Linnaeus? Of course, some changes to the old system had to be made.

    Cladistics retains much of the old Linnaen terminology.  Species are still defined as interbreeding populations and given binomial titles.  In this book, we even use such designations as "family" and "order" to describe groupings of species.  How, though, can one group together genera within an family, or families within an order?  Since Linnaeus, biologists have created a number of intermediate groupings like "subclasses" and "infraorders" for this purpose.  Such a process could potentially extend indefinably, with biologists naming "subsubclasses", "supersubphyla", or "subsuperinfraorders" to classify species with greater and greater precision.  What is more, if one believes taxonomy should be based upon evolutionary descent, then classes Mammalia and Aves should both be inserted into class Reptilia, since both mammals and birds evolved from reptiles.  Furthermore, with convergence making unrelated organisms look the same, and divergence making related organisms look different, who can tell how anything is related to anything else?

    Cladists wrestled with these problems (among others) through most of the 20th century, and emerged with a system, that while not perfect, provides some solutions.

    The fundamental idea of cladistics is that of sister taxa.  Sister taxa are pairs of groupings (species, genus, etc.) that share some distinctive trait, as in Linnaean taxonomy.  The difference between this cladistic classification and a Linnaean hierarchy is that the cladogram is fractal, it looks the same at all levels, with sister species, sister genera, sister families, and so on, all the way to sister domains, the most basic classification of life.

    To use the example of the greater hmungo, a cladist would designate this species as the sister of the sludger, since the two species are nearly identical.  Sludgers are slightly smaller than hmungos and live in swamps, while hmungos prefer the open prairies, but the differences that separate these species are very small.  The least hmungo, smaller still, is the sister of "greater hmungo+sludger", while the shambla , a Eurasian species, is a different genus, and so forms a sister to "(greater hmungo+sludger)+least hmungo".  That entire assemblage, the hmungos, in general, is the sister of the galumphs , while the galumphs and the hmungos together form a sister to the deer-like stellosaurs .  All of the cladograms of this project were constructed according this same principal, and at a glance will show the relationships between the organisms we have described.

Cladogram

(Text by Daniel Bensen)

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