The Category Conundrum

We were watching an extended version of QI last night, and one of the questions was,

“Which is more ‘mammaly’; a mouse or a hippopotamus?”

As was discussed on the show, given a few moments thought, both are mammals, so one should not be more or less mammal than the other.  However, it seems that the average human categorises a mouse as a mammal more easily than they do a hippopotamus, probably because hippopotami are slippery and water-dwelling.  Similarly, we apparently consider robins and swallows to be more ‘birdlike’ than flamingos and penguins.

Whilst we might feel a bit silly having to spend a few moments to decide which is the ‘right’ category for a hippopotamus, this is actually completely reasonable; what our brains are doing at this point is recalling and applying a certain set of criteria originating, in these (British) parts, from the Linnaean taxonomical system.  We Brits are normally taught at school that mammals are warm blooded, give birth to live young and feed them milk via mammary glands.  Years down the line, and certainly if one is not inclined to think extensively about animals in the slightly obsessive way that I do, it is easy to forget that classificatory systems like this are not an exact science and, even now, are liable to change.

As it turns out, mammals aren’t the best example for this blog as they have been fairly stable in Western scientific classification for quite some time, though I understand there is some quibbling about the subgroups (those monotremes  – platypuses and echidnas – are tricky; they are warm blooded and they do produce milk, but they also lay eggs and lack nipples…) Echidna. Photo Credit: Ester Inbar

More contentious, and I think more interesting, is the classification of species.  I learned at University the widely accepted biological definition, that a species is defined as a group of organisms that share a gene pool, so are capable of interbreeding and producing fertile young.  In theory, individuals from different species cannot; the classic example is that a donkey and a horse can mate, but they produce a mule or a hinny, which is normally – thought not always – infertile.

However, in the modern biological community it is quite openly admitted  that this definition is a little ‘fuzzy around the edges’.  Hybridisation, or species crossing, has been found to create ‘new’, fertile species. It is thought that the American Red Wolf is in fact a hybrid of the grey wolf and the coyote.  This has been identified by genetic analysis, which allows biologists to identify which species share a common ancestor.

Of course, we all share a common ancestor or ancestors, if you go back far enough.  Evolution is a very slow process that has resulted in millions of hybrids and branches and failed species and – a key point – continues to act on existing species.  Ducks, for example, are frequently crossing the species boundary; many duck species can (and do) successfully interbreed with others, producing hybrids while also maintaining populations of species with clear physical and behaviourals differences.   There is also reasonable genetic evidence to suggest that all modern, non-African humans carry Neanderthal genes, which suggests that we were a partial to a little hybrid action ourselves in days gone by…

Only certain species, notably humans, like to categorise and separate things, fitting them into boxes.  This undoubtedly has many uses, but also allows us to fall into the trap of believing that animal groups and species are fixed, static, completed articles.  This leads to a number of questions about the purposeful human preservation  of certain animal species, a topic I’m sure we will come back around to at a later date!

As useful, detailed and consistently developing as the Linnaean taxonomic system is, it is not the only way that humans categorise other species.  My favourite example is that of the Karam in New Guinea, who have a ‘bird’ category but do not place the cassowary in it. Casuarius Casuarius   I’ve included a cassowary picture here for your perusal.  (I am hugely paraphrasing here from the anthropologist Ralph Bulmer, who wrote a classic paper on the topic in 1967).  In the worldview of the Karam, the cassowary is given its own special classificatory group.  From a physical standpoint, the cassowary is seen as separate from birds and bats because it doesn’t fly (in fact, it doesn’t even perch; it is a very grounded sort of creature), has essentially no wings, appears to have hair rather than feathers and is substantially bigger than any other bird or bat in New Guinea.  It also has very strong, heavy leg bones, which quite resemble those of humans.

So, it is not perhaps unsurprising that – in the same way that an echidna does not, at first glance, lend itself to categorisation as a mammal – the cassowary is not necessarily a bird to the Karam.  There is a second principle, though, that is maybe even more significant to the consideration of how we relate to other species; the Karam hunt the cassowary  in very particular ways and have a lot of specific rules and regulations about how and when cassowaries can be hunted and consumed (or at least they did at the time of Bulmer’s article).  They therefore require a separate, unique categorisation for these birds, to account as much for their cultural significance as their biological oddities.

Despite having the Linnaean system widely taught and practiced here in the UK, we are not exempt from this kind of cultural classification.  A domestic dog, Canis familiaris, of the class Mammalia and the family Canidae (dogs), is also a ‘pet’; which means that we feed them, train them, groom them, often love them and generally don’t shoot or eat them.  The red fox, Vulpes vulpes, on the other hand, is also in the dog family, but is a whole different kettle of cultural fish.  I mean, mammal.

So, next time you are asked to classify an animal, you will now know how to completely over-think it and miss the next ten minutes of QI…



4 thoughts on “The Category Conundrum

  1. […] a relationship is lengthy or involved enough to be classed as symbiotic.  This returns us to my previous post about classification, and I would stress that this is a ‘rough guide’ only; the world is really too complex to […]

  2. […] A lighthearted post today, but before I go, a couple of bits and pieces I’ve thought about as a result of this topic.  Firstly – and I might look into this further at some point – I am interested in the level of interaction we need to have with a nonhuman to decide that it is worthy of a personal name.  I think it probably key that the object of our naming demonstrates a certain level of individuality;  without much thought, I named all of my demodex Dexter in the recognition that I wouldn’t be able to tell them apart, even under a microscope.   I don’t know much about the psychology of names and it’s too late to start reading up on it now, but I would suspect that our penchant for labelling things falls under a similar scope as our need to categorise. […]

  3. […] will also scavenge from humans on occasion).  Interestingly, there is continuous debate as to how different three of the small cat ‘species’ actually are, i.e. African and European wildcats and domestic cats.  They interbreed without apparent difficulty.  […]

  4. […] obviously, when you look at it) a bat.  As well as being linked to our slightly OCD habits of putting things in boxes, I think this cross-referenced naming is also related to the tendency of evolution to be highly […]

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