When is a bird a fish?

Look at the picture.  You might recognise the bird as a puffin, but even if you didn’t, I bet you still recognized that it’s a bird, and would probably be a little surprised if I told you that it is actually a fish.  Confused?  Well there is an explanation…

Traditionally, Christians avoided eating meat during the festival of Lent and on Fridays (a ritual still practised by many today).  However, they were free to eat fish if they wished.  For the inhabitants of Northern Scotland, for whom the puffin was a major part of their diet, not eating them presented serious problems (the Lent festival lasts 40 days).  To help out, the church authorities ruled that puffins, because they spend so much time underwater, were not birds, but were, in fact, fish, and could be eaten.  Good news for the puffin-eaters, bad news for the puffins.

What’s in a name?

The puffin story is a great example of how the naming and classification of living organisms can make a big difference to how we treat them, but there’s more to classification than that.  The ability to recognize and sort things is a vital survival skill, and isn’t limited to humans.

The bright markings of the poisonous monarch butterfly that warn predators not to eat it; the black and yellow “danger” stripes of a wasp; the rainbow colours of a South American, poison-arrow frog; these all work because the potential predators learn the significance of the patterns and file them in their memories as dangerous.

The ability to identify plants as either edible or poisonous; to tell the difference between a lion (harmful) and a sheep (edible); to recognise the warning hiss of a snake; these are all vital skills that have developed because they lead to a long and successful life.

Aside from the value of classification as a survival tool, we humans have taken it to extra-ordinary lengths.  The science of taxonomy, a branch of biology dedicated to the naming of living thinks is the ultimate refinement of this.  So far, we have identified around one and a half million living things, and sorted them into groups.

You are already pretty good at classifying living things, animals in particular (you can probably recognise and name several hundred).  But this is really the tip of the iceberg.  If you want to really study biology, you’ve got to get to know a bit of taxonomy.

What’s that bird called?

Identifying different types of plants and animals in a way that could be understood by all became important the minute scientists wanted to start sharing information.  The ancient empires of India, South America (the Aztecs), China and North Africa (The Egyptians) all developed systems for classifying the natural world.  The biggest impact on Western science was, however, the recorded work of the Greeks and Romans.

Over two thousand years ago, the Greek philosopher, Theophrastus wrote “Enquiry into Plants” and “The Causes of plants”.  He wrote about over 500 kinds of plants, and Alexander the great sent him specimens from the land he had conquered so that they could be studied.

The work of the Ancient Greeks was continued by the next great empire builders, the Romans.  Pliny the Elder wrote a hugely influential book, “Natural History”, dealing with the medical and agricultural uses of plants.  Another Roman philosopher, Dioscorides followed this with “Materia Medica”, a book that listed and, for the first time, grouped together over 600 plants useful in medicine.  Amazingly, this remained the most comprehensive work on the subject for nearly 1500 years.

Too many names

During the seventeenth and eighteenth centuries, explorers who had voyaged from Europe, returned with incredible numbers of plant and animal specimens that had never been seen before.  The job of naming them all and describing them fast become a major headache.  Scientists realised that it was time to get organised.

There are two reasons why scientists try to be organised about the naming of living things.  Firstly there are too many for any one person to learn the names and descriptions of them all.  Secondly, for many, there is a different name in every language.  If I were to talk to one of my French friends about the badgers that live in the woods by my house, they wouldn’t know what I meant.  If, however I used the French word Blaireaux, they’d understand me.

Credit for solving the classification headache goes to the Swedish scientist Carl Linnaeus.  In 1735, he invented the Binomial (literally, two-name) identification system that, with revisions, we still use today.

Linneus proposed that all animals and plants should have a “scientific” name that everyone would understand and use.  To prevent arguments, he based these names on Latin and Ancient-greek.  The use of Latin didn’t cause problems because, at that time, all scientists learnt Latin so that when they wrote to each other they could use a common language.

The really clever thing about the Linnean system was the way he sought to place organisms in groups based on their similarities.  Under his system, a lion, became Panthera leo.  Notice how I have written the name in italics, this is so that scientists – that’s you by the way – can spot straight away that I have written a scientific name and not a common name.  The second word, leo, is the unique “species” name of the lion.  The first word, is the “genus”, or group of similar animals to which it belongs.  Just by looking at the name, I can make an educated guess about the kind of organism it is referring to, even if I’ve never seen it.  For example, do you know what a “Tendwa” is?  I thought not.  You probably wouldn’t recognise this animal by its scientific name Panthera pardus either, but that doesn’t matter, because you know that if it’s in the Panthera  group, its going to be quite like a lion and therefore not something you want to play with (in English, its called a leopard by the way).

Happy families

Linneus didn’t stop at grouping things by Genus, he built larger and larger Taxa (groups), so that each scientific name became like a postal address that identified exactly where on the tree of life an animal or plant should be placed.  This innovation was the principal reason his classification system caught on, and is still used.

Stop for a second and think about how a postal address works.  If my friend Theresa wanted to send me a postcard from Australia, where she now lives, she would write my address on it: Howie Watkins, PO Box 15, Neath. Wales. UK.  When she posts it, it will be taken to the local post office and sorted.  The person who sorts the mail in her town wont know who I am, and may not even have an idea where Wales is, but will know where the UK is and will stick the card in the next bag of mail heading in that direction.  When the bag is opened at the airport, it will probably be opened by someone who doesn’t know me either, but they’ll know where Wales is, and they’ll send it another step closer.  The mail sorters at Neath Post Office do know who I am, and do know where PO Box 15 is, so they’ll deliver the card.  The system works, even though it’s impossible for one person to know the exact location of everyone else on the planet.

To see how a scientific name works in the same way, here’s the full name for an African Lion: Animalia, Chordata, Vertebrata, Mammalia, Eutheria, Carnivora, Felida, Panthera leo.  That’s a bit of a mouthful I know, so here it is, step by step.

  • The Genus Panthera (Jaguars, leopards, tigers & lions) fits within a “family”, felidae, which contains all the world’s cats, everthing from a pet pussy to a Siberian tiger is in this group.
  • The family felidae is one of several within the “order”, carnivora, which also includes bears, dogs, badgers and sealions – to name a few.
  • The Carnivores are a large and varied group, but they all have common features.  All carnivores give birth to live, fully formed young, so are grouped within a “sub-class”, Eutheria.
  • Eutherian mammals all have a placenta, so that their babies receive their food directly from their mother’s bloodstream as they grow inside them.  There are some mammals that don’t do this (the marsupials for example: kangaroos, etc.) and some, like the duck-billed platypus that even lay eggs.
  • The next step up identifies the lion as part of the “class”, mammalia, along with all the other hairy, warm-blooded animals that have mammary, milk producing, glands to feed their babies.
  • All mammals have a backbone, so are in the “sub-phylum”, Vertebrata, which is part of the “Phylum”, Chordata, a group that includes all animals with a central spinal nerve running the length of their bodies.  This is one of many phyla within the animal kingdom (or Kingdom animalia, to be absolutely correct).

As more and more living things have been discovered, and we have learnt more about them, it has been necessary to make some quite major changes to his original classification.  Despite these changes, Linneus’ basic plan is still followed and he is still referred to as the father of Taxonomy.

Which kingdom am I?

Well I don’t know about you, but I’m definitely an animal.  I have to eat to stay alive (I can’t photosynthesise), I can move about, I am made up of many cells, all working together, that couldn’t survive on their own and those cells, when viewed through a microscope contain definite and complex structures.  Plants are very like animals, except that they don’t move about, don’t need to eat to stay alive (they CAN photosynthesise) and have cells with a tough cell wall made from cellulose.

Back in the eighteenth century, everything was placed into either the plant or animal kingdom.  However, as we have discovered more about how organisms function and we have built microscopes capable of looking in detail at the insides of cells, we have come to realise that there are living things on earth that are too different to be placed in either of these two groups.  In order to cope with this, scientists now use five kingdoms: animals, plants, fungi, protists and monerans.

This group includes the bacteria and some really odd organisms called blue-green algae.  All monerans are single celled.  All have cells without a complex internal structure.
Protists are single-celled organisms, however some form colonies.  They have cells with a complex internal structure
Fungi have cells that are quite similar to those of animals (with a complex internal structure) but there the similarity ends.  Fungi don’t move about and can’t photosynthesise.  Mushrooms, mould and yeasts are all fungi
Multicellular, move about, cells have a complex internal structure, need to eat – can’t photosynthesise.
Multicellular, don’t move about, cells have a complex internal structure, cells have a cellulose cell wall, don’t need to eat – can photosynthesise.

Some scientists argue that even this five-kingdom model is too sloppy and instead use a seven or even seventeen kingdom system.  For most purposes however, the five-kingdom system works best.  One thing you learn with taxonomy is that nothing is set in stone, the groups we use to classify organisms are not natural, they were created by us to help us better understand how the world works.  At best they are imprecise, at worst, completely mis-leading.

Changing the rules

Charles Darwin’s theories on how species were formed were published in his book “The Origin of Species” (1859).  They had a big impact on the way scientists grouped organisms together.  Before Darwin, it was generally believed that a god had created all living things on Earth and had made them the way they were.  However, according to Darwin, species evolved over time from one form to another, a result of a random change and the battle to stay alive.  Since it’s publication, Darwin’s book has caused, and continues to cause, controversy around the world.  Many religious fundamentalists (people who believe absolutely in their holy books) still reject them.  His work has led to many changes in the way species are classified.

After Darwin, classification stopped being something that merely made the job of naming animals easier, it became a way of describing how closely related different species were to one another, a way of understanding how evolution might have taken place.  Once you accept that species evolve, and can become extinct, you can start to make sense of the similarities and differences between the organisms that surround you.

The concept that all living things were connected, related to one another to differing degrees is now fundamental to how species are classified.

New tools, New discoveries…

Darwin’s theories were based on the observation that parents passed on their characteristics to their children.  At the time, no one understood how this actually happened, but now we do.  In every cell of every living thing there is a chemical that contains all the information that makes that organism the way it is, DNA (Deoxyribonucleic Acid).  The importance of DNA, and its role as the “blueprint” of life was finally understood in the second half of the twentieth century..  Since then, research in molecular biology, looking at the structure and function of DNA, have forced yet more changes in the way organisms are classified.  Today, scientists compare the DNA of different species to decide how closely related they are.

As our techniques for comparing DNA become more sophisticated, and the number of organisms whose DNA has been analysed to some degree becomes greater, the address map to the tree of life is going to need changing.  Each change we make will help us better understand how the world came to be the way it is.  Some of these changes might not be popular however.

The use of comparative DNA analysis has led to some uncomfortable truths being uncovered.  For example, our closest living relatives in the wild are the chimpanzees.  It has long been thought that humans and chimpanzees are both descended from a common ancestor that lived, somewhere in Africa, around five and half million years ago.  Just how closely related we are to our hairy relatives has, however, been a controversial point since Darwin originally suggested it.  The latest studies of chimpanzee and human DNA reveal that there is a startling similarity between the two.  Initial research suggested we were >98% the same, however, more detailed studies, using the latest (more accurate) techniques have led to this being reduced to ~90%.  That is still a lot of similarity, and has led to calls from some scientists that we should re-classify ourselves.  At the moment, there are two species in the chimpanzee genus: Pan troglodytes (the common chimpanzee) and Pan paniscus (the pygmy chimpanzee).  Humans, have their own genus, we are the only surviving member of the Homo group, Homo sapiens sapiens (the third word in the name indicates that we’re actually a sub-species).  This, it is argued, should be changed.  Because we are so closely related to chimps, we should more properly be classified as part of their family.  Perhaps, humans should stop thinking themselves special and accept that they are little more than a chimpanzee with a big brain and no hair, Pan homo sapiens perhaps.  Banana anyone?