Part One: WHAT IS A SPECIES?

            It is a universal that all cultures, all societies, from the bowels of the rainforests to the edges of tundras, all entertain a taxonomy.  But what is taxonomy?  Is it something they do at Revenue Canada? A quick definition: it is a system of naming and categorizing organisms.  Now, of course, some taxonomies are more rigorous, and/or more complete than others. It is useful, then, to distinguish scientific styles of taxonomy vs folk taxonomy.

            Scientific taxonomies spell out the details that define whether or not the animal intruding in your garden is a bird or a cat. We ask: does it have fur or feathers? Four legs vs two legs and a pair of wings? Can it lactate?  Etc... And so, given an adequate description of the animal in question, and comparing these features against lists of features that define other organisms, we might come up with a match and decide: "Aha! This is a yellow-bellied searsucker!"  If you don't come up with a good match, then you've either discovered a new kind of critter, or, more likely, you’re mistaken somehow.

            Folk taxonomy, on the other hand, is more holistic in nature, and makes no pretense to be exhaustive in scope. What gets named are the organisms that are of importance to the society doing the naming. A fishing tribe, for example, would probably distinguish a pike from a muskie, but arguably have the same name for, say, several species of ants. Nor would they to bother make long lists of characteristics that would pinpoint one organism into one category and not another. The classification just 'feels' right. Of course, if pressed to defend their choice of grouping, say, crows and ravens to the exclusion of butterflies, they would point out key differences to justify their choice.  Or think of an eight-year old child who would put tigers and lions in the cat family, and not antelopes. If asked why, he'd might just reply  "Coz they're more catlike", and leave it at that.

            Folk taxonomies have been studied a lot this past decade, and it turns out that, within their cultural scopes, they coincide quite well with scientific taxonomies. That should come as no surprise. Human beings are very observant, and have minds pre-disposed to categorize things left, right and centre. These two elements combined can (and do) produce sound taxonomies

            However, scientific taxonomies are far more ambitious than their folksier versions. Here, everything in living nature has to be accounted for, and described in great detail. Furthermore, scientific taxonomies tend to be very formal and logical, and have a specialized nomenclature (a set of words for narrow, but well-defined concepts).

            The taxonomy system most of us are familiar with is the classification of organisms into Kingdom, Phylum, Class, Order, Family, Genus and Species.

            This classification by hierarchical categories has its roots in the system devised by the eighteenth century Swiss naturalist Carolus Linnaeus, and is called the Linnaean System, in his honour. It's all very pretty and detailed, but is it useful? Does it reflect some 'truth' in Nature? In other words, is it any better than classifying animals alphabetically, where boas and bacteria are classed 'Beeoids' because their English names start with the letter 'B'?

So let's take a closer look at this system and start with its basic building block, the Species class.

            As conceptualized by ancient Greeks, such as Aristotle and Plato, as well as Linnaeus himself, a species is an instantiation of an abstract universal, (the eidos) , an underlying template on which small variants are built on. Each organism, then, is a small variant on its 'species' theme.  This concept works fine for folk taxonomies, because, after all, a rose is a rose is a rose. However, in the case of modern biology, with evolutionary theory and genetics as cornerstones,  something more is needed,  something that will capture the idea that species are in flux, not constrained, capable of change. If new species are to arise from other species, this is crucial, for how else would evolution occur?

So, here is a quick definition of species, one that satisfies modern science:

            " Species are groups of interbreeding natural populations that are re productively isolated from other such groups."  According to this concept, then, the members of a species constitute (1) a reproductive community.  The individuals of a species of animals respond to one another as potential mates and seek one another or the purpose of reproduction. A multitude of devices ensures intra-specific reproduction in all organisms. The species is also (2) an ecological unit that, regardless of the individuals composing it, interacts as a unit with other species with which it shares the environment. The species, finally, is (3) a genetic unit consisting of a large intercommunicating gene pool, whereas an individual is merely a temporary vessel holding a small portion of the contents of the gene pool for a short  period of time.

            But what about the 'higher' taxonomic units, like Family and Order and all the other ones? Here, the definitions are often conflicting, as these units seem  to be more and more on the arbitrary side of things. However, they cannot be summarily dismissed, as they must reflect something real (my opinion), for the class of 'Birds', for example, cannot be so easily done away with because that taxonomical unit is not so easily defined scientifically.  Just the same, there are some taxonomists who would view these class distinctions as being without merit, and maybe the idea of 'Fish', as far as evolutionary theory is concerned, is not a useful concept. There is actually a big debate here, and I won't go into it, and save my breath to speak only about species, and their role in evolution, namely in the process of speciation—i.e., how do species evolve?

            There is a consensus that allopatric speciation is the driving force behind evolution. What does 'allopatric' mean? Is it some hockey fan phoning up his favourite goalie, blustering "Allo! Patrick!"? Actually, it loosely translates as  “other place”.

            Here, we have a close analogy in the evolution of languages. Can you imagine if the castaways on Gilligan's island had never been rescued (very likely) and had started to reproduce (egads!).? Simplify the scenario by assuming the radio finally bit the biscuit, and also that illiteracy became the norm (I'm imposing these two conditions to ensure that the castaways and their descendants would be totally isolated from the world they originated from). Now, after 15 generations, how much of the language they'd be speaking would be recognizable English? Probably very little. The new 'Gilliganese' would be related to English in the same way as, say, French is to Spanish. Related, yes, but mutually unintelligible.

            Allopatric speciation works the same way. If a bunch of members of one species somehow gets separated from the rest of the population, then the cumulative effect of small genetic changes, over the course of several thousand years, would alter the nature of their modified genetic pool sufficiently to make them 'unbreedable' with the parent population. A new species would arise.

            In relatively stable times, these barriers would tend to be small in scale, so that though speciation would occur through allopatric means, the number of species arising  would be nothing compared to the  number that would arise when very large and wide barriers impose themselves, say,  after a 'global' change such as the splitting up of continents, big drop/rise in sea-levels, or asteroid impact.

            Now, these rates of speciation lie at the heart of the punctuated-equilibrium debate. It makes for fine armchair paleontology, but does the fossil evidence support it? The jury (as far as I'm concerned) is still out on that one, pending more hard evidence from Stephen jay Gould and company. For one thing, how well does the fossil record record speciation (and rates thereof) . And, closer to the heart of this talk tonight,  how does one determine what a species is, based solely on fossil remains???

Species in the fossil record.

            When you compare two fossil trilobites, and they seem identical, then it's easy to feel confident that they belong to the same species. However, it's often the case that they're not, and you're left wondering "Do they belong to the same species or not?". How much do they have to vary before you split them? It's a hard choice, and your level of familiarity with these critters is usually your first obstacle.

            I've often experienced that sinking feeling of spirits when I hear somebody who's a stranger to trilobites, who, when looking at my collection for the first time, say something like "Gee! How can you tell the kinds apart? They all look the same to me..."

            At this point, I make a point of selecting two unmistakably different species of trilobites, and point out the differences between the two. Once my guest has satisfied himself that he can differentiate them, I move on to less obvious contrasting pairs, and have him hone his skills there. Comes a time, however, where one wonders if the slight differences are sufficient to justify saying you have two species.

            As mentioned in the definition of species,  any given individual is just a subset of the gene pool that defines that species. Different sub-sets, different looks. Not too different, but somewhat different. Take a look at the small differences there are within Homo sapiens. Disregarding the unscientific rants of racists, and you'll note that the differences, though there, are quite minor. A 6'4" tall person is just a small percentage taller than the average. Skin colour, though more striking because it's 'all over you' , is  mere variation in pigmentation. The dimorphism between our sexes? Hey, my nipples stick out when it's cold too.

            Other than the gene pool sub-set effect , there's other things that can influence one's looks.

For one thing, there's age. Juveniles are rarely mere miniaturized copies of their adult counterparts. In the case of insects, the differences are unbelievable.

            Disease is another issue. Recall how an early reconstruction of Neandertal erred greatly as it was based on the remains of a severely arthritic individual.

            The environment you grow up in also has an effect on your looks. Deep tan or ghostly skin? It was also recently noted that asaphid trilobites look different depending at which water depth they lived in: they get broader and have more terrace lines the deeper they lived. This is called the ecophenetic effect.

            Convergent evolution is where different species wind up with similar looks as they both adopt a similar body plan in response to a shared environment. (Here, show slides of various ‘convergent’ critters). Normally, these differences are superficial,  as the nitty-gritty details of their respective anatomies reveal disparate relationships, but that’s more difficult to pin down when the organisms in question happen to be closely related—this is parallel evolution.

            As you can see, these variables  can make species assignation suspect.  So how confident are we that our narrative of Natural History is correct?  The answer is, surprisingly, moderately confident.

Let me explain through a small divergence.

            Let’s say that you’re asked to estimate the numbers of  chimney sweeps in the Ottawa area. Pulling out a number out of the air would be out of the question; you have to make an educated guess. I  posed this challenge to myself, and this is how I arrived at a number.

            First, I guessed the number of people in the NCR to be about a million.  But how are they divided up into households? I figure the average household to be about three ( a balance between families and all these single people). So we’ve got 300,000 households. How many of these households are actually houses? A lot of people live in apartments, residences, retirement homes, etc… So let’s say, then., that there’s something like 150,000 houses in the area. Of these, how many have chimneys? If half, that leaves 75,000 houses that might require the services of a chimney sweep. But even here, probably most of these houses don’t actively use their chimneys, leaving us with, say,  20,000 houses. On a yearly basis,  I’ll guess that  4,000 get their chimneys cleaned ( people only clean them every few years, and some never bother). If a chimney sweep could do two houses in a day, and say that there are about 150 days of the year where chimneys get swept (because of Sundays, holidays, bad weather, winter), then a typical sweeper would do 300 chimneys in a year, meaning that the Ottawa area would require about  twelve full time chimney sweepers.

            So I checked the phone book, and found that the number of actual chimney sweeps is very close to my estimate!

            The same applies to species assignation.  Though the specifics may be blurry, our mistakes tend to cancel out and we wind up with a fairly good picture. And yes,  paleontology is awash with guesstimates,  but it still is, in the long run, a solid science.

Frank Habets