Organism Classification: What and Why

I enjoy reading the search terms that people use to end up on my blog.  Occasionally they interest me enough to write a post about them.  This is the result of one such event.  The search phrase was “Why is animal classification important?”

It got me to thinking.  Why is classification important?

I dealt with some historical aspects of high level classification here.

Within a species is a continuum of genetic differences.  In the case of clines (also called ring species), the continuum is such that organisms at one end of the ring cannot interbreed with species at the other end… yet all the intermediaries can interbreed.  The following explains it:

A –> B –> C –> D –> E –> F –> G

So species A can breed with B.  B can breed with C, etc.  Occasionally, you might see A breed with C and B with D, but that’s about the limit.  A cannot breed with F or G, thereby eliminating one of the primary definitions of a species, that is organisms that can interbreed.

On the other side of the coin are different species,  Obviously different species  that can interbreed and produce fertile offspring.  Like lions and tigers, whose offspring is a liger (which is an epically cool animal).

So, what’s the point?

The first thing to keep in mind, is that biological classification is not (as currently practiced) an arbitrary statement.  Organism A goes in this bucket, while organism B goes in this other bucket.  [With the provision that Kingdom Protista is pretty much a bucket that organisms that don’t fit in any other kingdom get dumped into.]

The relationships are based on shared, homologous characters and genetic similarity (also evidence of common ancestry). 

A homologous character is something that has a shared common ancestor.  The fore-arm bones of all tetrapod animals, for example, are remarkably similar between even wildly divergent groups.  The same bones can be seen in birds, whales, frogs, humans, horses, etc.  This concept was one of the earliest supporting evidences for a common ancestor.  Now some structures are not homologous, even though they do the same thing.  These are analogous structures.  For example, the wings of a beetle and a bat.  Not even close to being the same thing, but since they have the same function, they are analogous. 

Genetics plays a huge role in modern biology.  When organisms can be identified as closely related genetically, then you can do a lot of things to help them.  For example, a recent study found that the Florida Panther is not a different species from the mountain lion.  This allows cougars to be moved to Florida to increase that population without danger of creating hybrids (like the liger above).

Knowledge of these relationships are useful in a variety of ways.  Just a few examples, why practice surgery on a human, when you could practice on a pig?  They are remarkably similar in most respects.  Rats and mice have many homologous systems with humans, making them ideal organisms to use in laboratory experiments.

With all that being said, why classify things? 

The first reason that I can think of is ease of communication.  If I say that I have found a new species of the genus Ochotona (cute aren’t they?) then you know that I’ve discovered a creature with the following characteristics:

  • small
  • rounded ears
  • furry
  • herbivore
  • a specific dental formula
  • and will probably live in a colder environment

All that from the word Ochotona.  If you are really familiar with the genus, you could know a lot more (evolutionary history, unique proteins, unique bone structures, etc.)  just because I was confident enough to say it belongs in a particular group.  Instead of me having to describe all of that, I told it to you with one word.  That is an amazingly powerful concept, when you think about it.  Just try to describe the difference between a dog and a cat to someone who had never seen either.  It’s harder than it sounds just because you have internalized the differences and rarely think about them.

If we can classify organisms into similar groups, then we do not have to examine every organism on Earth to trace relationships among and between groups.  For example, we don’t have to perform a complete genetic sequence on every member of the genus Canis to be able to compare them with other groups (like Felis and Ursa).  Instead, a representative is sufficient.

There are other reasons, but they break down into simplifying specific knowledge into general patterns and predictions about organisms based on their classification.

Besides it’s fun.  You can annoy your friends by endlessly listing the genus and species of animals you see on TV. 

I hope that helps.

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