Wildlife Online - How We Classify Organisms - 2 views
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Generally-speaking, we humans have a desire to label and categorize things
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We name objects because it makes our life easier. Let’s say you’re sitting on the sofa and you want your friend to pass the remote so you can see what else is on the TV – this process is rather difficult without names. A request like, “Please pass the thing on the thingy. I want to see what’s on the whats-am-a-jig”, is likely to meet with confusion. The request is easier for the other person to follow if things have names: “Please pass the remote on the coffee table. I want to see what’s on the TV”. Now, it’s true that you might be able to gesticulate at your friend until he or she either gets the idea, or misinterprets and takes offence, but what if you can’t see the person you need help from – charades doesn’t help then. Imagine that you’re sitting on the train going to work when you remember you forgot to get the pie out of the freezer to defrost in time for dinner; fortunately your partner has the day off and is at home. So, you phone up and ask “Can you get the thing out of the thingy so it’s thingy-ed in time for what’s-its-name?”
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So, the act of naming is a matter of convenience – whether the objects are pieces or furniture, bits of machinery, or animals we assign them names because it makes life a heck of a lot easier for us. We, for example, call a ‘fish’ with a cartilaginous skeleton and between five and seven pairs of gills a “shark”. This allows us to tell another person what animal we’re looking at or talking about. The use of a name certainly helps, but not without problems. Telling someone that you went diving with sharks while on holiday is kinda like saying you went out for dinner with some primates; it’s not quite as specific as we might want because there are lots of different ‘types’ of primates (and sharks). Consequently, to make our meaning as clear as possible, objects (be they animals, plants, bacteria, furniture, tools, etc.) are split into as narrow groups as possible and each group is given a name. So, for example, the group of ‘fish’ we call sharks gets further split up into different types of sharks based largely on how they look (their “morphology”), both internally (i.e. their skeleton, internal organs etc.) and externally (i.e. fins, gills, skin, colour etc.). Large groups are then split into smaller (i.e. more specific) ones and so on down the line until you have a group containing all the animals considered to be exactly the same in terms of the features we’re looking at (these can be morphological, genetic, ecological, biochemical, even behavioural): this is the species level (we’ll look at this in more detail later). Humans, chimpanzees, great white sharks, blackbirds, palmate newts and red squirrels are all examples of species. Some taxonomists opt to take the splitting below the species level and group animals into subspecies, infraspecies and forms (among others). Perhaps the extreme of this splitting is found in the human species, where every individual of the species is given his/her own name at birth. The problem is that this gets very complicated very quickly as the list of viable names soon runs out and leads to the confusing situation of several individuals with the same name – think how confusing it can be if there are two or three people in the office with the same name. Consequently, the branch of Science known as “Taxonomy” (from the Greek word taxis, meaning “order” or “rank” and –nomia, meaning “law”) is largely concerned with the grouping of organisms down to the species level.
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This process of giving each species a name is all well and good (it certainly makes it easier to be precise in our communications), but there’s a snag. In order for the system to work, everyone must call that “something” by the same (universally agreed) name – if the process isn’t regulated we can run into problems. Such problems are rife with “common names”. Here in the UK, we have an awesome bird of prey called a Peregrine falcon (the fastest bird in the world, clocked at speeds of 87mph / 140kmph during a dive - left). In North America, however, the same bird is more commonly known as the Duck hawk, after its impressive ability to nab ducks in mid-air. Anyone who wasn’t aware of this ‘double identity’ could reasonably assume that we were talking about two different species. The problem gets exponentially more complicated when local names, different languages and different dialects are taken into account. So, how do we get around this? Well, we do it by giving most species known to Science two names: a vernacular (common) and a scientific (often referred to as Latin, but more accurately a Latinized-Greek) one. While it’s true that not all species have a vernacular name (e.g. many bacteria, mosses, lichens etc.), this isn’t a major issue because it is the Latin name that’s the important one; it’s designed to remove confusion caused by dual identities.
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Carl von Linné (also variously referred to as Carl Linnaeus, Carolus Linnaeus and, more colloquially, the ‘Father of Taxonomy’), is largely responsible for the way we classify creatures today.
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The system comprises a series of levels, or categories, called taxa (singular being taxon) and assigns each species a binominal name. All scientific names ascribed to species are initially binomial (i.e. they are composed of two parts), consisting of a generic (i.e. genus-related) and a specific (i.e. species-related) epithet
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We now recognize six kingdoms: Plantae (plants), Animalia (animals), Fungi (fungi and moulds), Eubacteria (the bacteria – sometimes called Monera); Archaea (microbes similar to bacteria); and the Protista (something of a dumping ground for all multi-cellular organisms that don’t fit into any of the aforementioned groups – sometimes called Protoctista). Despite some quite apparent differences between the two, a few textbooks merge the Eubacteria and Archaea into a single kingdom: the Prokaryota.
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Depending on the scheme you choose to follow (and they’re changing all the time!), the kingdoms break down roughly as follows: * Plantae is divided into about 12 phyla and comprise about 270,000 species. * Animalia is split into about 33 phyla and contains about 800,000 species (although this is probably a drastic underestimate of the true figure). * Fungi have five phyla and about 100,000 species. * Eubacteria have three phyla and a number of species that is difficult even to estimate – some authors suggest 1,000,000,000 (a billion) but even this could be a considerable underestimate! * Archaea are poorly known and there are currently three main (and five tentative) phyla that have been created based largely on laboratory cultures (estimates of total phyla range from 18 to 23). The most recent list I can find (1999) contains 209 species. * Protista comprise some 20 to 50 phyla and about 23,000+ species.
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Great White (right). Kingdom: Animalia (mobile critters; have many cells; can’t make their own food) Phylum: Chordata (flexible skeletal rod with accompanying nerves) Class: Chondrichthyes (‘fish’ with a cartilaginous skeleton) Order: Lamniformes (‘Mackerel’ sharks) Family: Lamnidae (‘Mackerel’ sharks) Genus: Carcharodon (from the Greek carcharos meaning “ragged” or “pointed” and odon meaning “tooth”) Species: carcharias (Greek for “shark”)