The classification of creatures

EPS 106, Sept 5^th, 2000

Last time we stated that all creatures are born from creatures – no spontaneous generation. We can also say that all creatures come from their own kind. Never does a cat have a puppy, always a kitten. One could say that “infinitely back in time, cats gave birth to kittens, and dogs to puppies”.

EACH HAS YOUNG LIKE ITSELF, AND ALWAYS HAS.

Different creatures are called species from the Latin for ‘outward appearance’.

Outward appearance can be misleading. Fox terriers breed fox terrier puppies. Poodles breed poodle puppies, but does this make them separate species? Obviously not! A poodle and fox terrier can interbreed, producing puppies with characteristics of each parent. These are different varieties of the same species.

People are the same. All can interbreed.

Not so with an elephant. One might think they are all the same, but an African and Indian elephant do not interbreed. In contrast, the Ceylon and Sumartra elephants, although looking quite different may be mated. They are varieties of a species. There are over 500 varieties of fleas. Each flea not only knows males from females, but also whether the species is the same. (Of course, an intelligent flea may say “how can a man tell a woman from a female chimpanzee? They all look the same”).

SO WE HAVE THE DEFINITION: IF THEY CAN BREED, THEY ARE A SINGLE SPECIES. RIGHT? Not exactly!

What about a donkey and horse? Their offspring are mules. Are they the same species? Lions and tigers can interbreed. But in both cases, their offspring are sterile. They are not viable.

There are also many species that probably could breed but don’t due to geographic. Numerous examples of birds (finches, etc.) are examples. Perhaps our best definition might be

“A biological species is defined as a group of natural populations that mate and produce offspring with one another, but do not breed with other populations.”

A take home point might be this: It is difficult to make a ‘clean’ distinction between species. Some are easy, like the two elephants, others are questionable.

Finally, the question arises, “If cats come from cats, was there a first cat?” If time is considered infinite, then the answer might be ‘no’. But more likely, at least in our Judeo-Christian society, it is easy to say that the answer is ‘yes’, and was created through some supernatural forces, as no previous pair of cats existed. Up to the early modern times, it was taken for granted that all creatures were created in the first week, and that they have never changed. In the Bible it says (Genesis 1)

“grass and herb yielding seed, and the fruit tree yielding fruit after his kind. . . great whales and every living creature that moveth . . . after their kind . . .” etc.

Each species had existed from the beginning and continued to exist unchanged to the modern times. This concept is the immutability of species. After Creation, species have never changed.

Until relatively recently, the immutability of species was a relatively accepted fact. Most people can only think of several hundred species, which couldn’t have taken Adam too long to name them all (Genesis 2: 19-20 – “. . .brought them (animal) to the man to see what he would call them: and whatever the man called every living creature, that was its name.”).

At the same time, it wouldn’t be too hard for them all to fit on the Ark, which was 300´´50´´30 cubits, about the size of a modern destroyer. Realize, that in the ancient world, this was enormous.

So, how many species are there? Most people can’t think of more than 100 – 200. Aristotle could only name ~500 species. No problem.

BUT, with time, more and more lands were discovered, and species as well.

By 1700 there were more than 10,000 species of plants and animals. (Tough to put
them all into the Ark).

1800 >70,000

Today: > 2,000,000 species (and probably an equal number not yet discovered). Even considering only mammals and birds, there are still tens of thousands of species. Tough for Adam, tough for Noah. But how else could one explain all of the different animals? The answer came slowly, and started with classification.

The very fact that more and more species were being discovered, made it harder and harder to keep track of them. A method of classification was necessary. This shouldn’t be too tough: Even a child can see certain similarities. When going to a zoo, he will say “look at the big pussycat” when seeing a lion or tiger. Clearly, they are not the same species. Any attempts to cross them would lead to disaster (for the pussycat). But they are also clearly related, as are lions, tigers, leopards, jaguars, lynxes, bobcats, cheetahs and ocelots. These make up the ‘cat family’.

There are an unlimited number of ways to classify them. We could group them as quadrupeds – four footed creatures vs. two footed. Land creatures and sea creatures. We could group pussycats and lions, or, perhaps pussycats and canaries, as both are household pets. (Canaries and domestic cats are ‘closer’ when it to feeding by hand!!).

Consider land creatures and sea creatures:

Sea creatures includes what? Do we put oysters (shellfish), starfish with the true fish? What about whales? If we say a fish is “any creature in the sea” then a whale is a fish. Aristotle noticed that dolphins and porpoises had lungs. They did not lay eggs, and they nourished their unborn young via a placenta. He grouped them with the quadrupeds rather than fish. (Aristotle was a lone voice. For over 2,000 years afterwards, his idea was lost, and whales were fish. Only in relatively modern times were whales put back with mammals.)

A bat is a similar ‘exception’. The bible lists the bats among the birds, because it is a flying creature that inhabits the air. This is fine, if this is how we chose to define our species. The accepted convention among biologists is to group bats with mammals, because they have hair (not feathers), give live birth with the aid of a placenta and nurse their young with milk. Instead we define birds as having feathers! (EVEN IF THEY CAN’T FLY).

Modern classifications: John Ray (or Wray) (1627-1705) is the father of modern classification. He was born in Essex, son of a blacksmith. Because of a trust fund, he was able to attend the University of Cambridge. He worked for 13 years on a fellowship, classifying plants, eventually losing the fellowship because he was a Puritan sympathizer.

Eventually he listed more than 18.600 plants. He had a scheme that was logical, which was an innovation. For example, he separated the flowering plants into monocots and dicots. The monocot or monocotyledonous plants have one leaf sprouting forth from the seed, the dicots, or dicotyledonous plants have two.

This may seem like a pretty trivial difference, but in fact it is an outward expression of a host of other distinct differences between these classes. It is still in use today. (Obviously, it is important to pick your visible signs carefully. To say that birds can be identified as two-legged creatures makes Man a bird. To call birds all animals with wings makes bats and flies birds. To say that feathered creatures defines birds hits the mark. All birds have feathers, and no other creatures do. . . dinosaurs?). Ray worked on animals as well, and was strongly influenced by the bible.

For example, the Bible states

“Whatsoever parteth the hoof, and is clovenfooted, and cheweth the cud, and among the beasts, that shall ye eat”

This represents a threefold classification:

Animals with hoofs and without hoofs. The later includes tigers, anteaters, etc. and would be unclean.

Of those with hoofs, the further division is cloven hoofs. Cloven hoofs are two hoofs per foot. One or three or more are non-cloven hoofs. Thus the horse (1 hoof) and the rhinoceros (3 hoofs) are unclean.

Cloven hoofed animals are then divided into cud-chewing (ruminates) and non cud-chewing (nonruminates). Cud chewing is the regurgitation of food that has been swallowed in haste for later, leisurely chewing. Non cud-chewing animals include swine (pigs) and are unclean. The cud chewers (unlucky guys) are cattle, sheep goats and deer.

This classification uses methods: anatomical and physiological. The first is appearance, the second is chewing the cud (physiological).

Ray went further. Of the ruminants, he divided them as to whether they had permanent horns (sheep, cattle, goats) and those with horns that are shed every year (deer). Much of what Ray did is still in place, but the major breakthrough couldn’t come for nearly a century, when Carl von Linné (also known as Carolus Linnaeus) invented modern taxonomy (from the Greek meaning ‘arrangement’).

Linnaeus (1707-1778) was a Swedish naturalist. He went to University in Medicine (University of Lund) and later Uppsala. He traveled throughout Scandinavia (including unexplored regions in the far north) observing different plants carefully. He started on plants, as did Ray. Starting in the early 1730s, he realized the difficulty in classifying all species, and started generating his own system. He determined the sexual parts of plants and developed a classification system. In 1737 he wrote Systema Naturae in which he attempted to classify all known species. He went further, however, because he put groups together, and grouped the groups, etc.

Similar species were grouped into a single genus (plural genera) from the Latin ‘race’. Genera were grouped into order .

Orders were grouped into Class.

Linnaeus had six animal classes: mammals, birds, reptiles, fish, insects and worms. Later, the system was expanded.

Classes were grouped into phylum (plural phyla) from the Greek word meaning ‘tribe’. Phyla were grouped into kingdoms.

Species

Genra

Order

Class Getting

Plylum more

Kingdom general

Linneaus had two kingdoms– plants and animals, as had Aristotle before him. Fungi were placed in plants, and single-celled organisms, while recognized, were not classified. It wasn’t until 1866 that a third kingdom was proposed, the Protista, or single-celled animals. Finally, in 1938, a fourth kingdom, Monera, was proposed, which included bacteria, separate from Protista. (The main difference (and it’s a biggie, is that Monera have no nuclei). In 1957, a fifth kingdom was proposed – the fungi. It was recognized that they had very little in common with plants. There has since been a 6^th kingdom proposed on the basis of molecular structures that indicates a very primitive form called Archaea.

A word about classification: Viruses are by themselves. Are they even alive? What is life? Prokaryotes: Kingdom Monera: Bacteria, cyanobacteria, cell walls, but no inner cell – no inner membrane. Eukaryotes: The DNA is in the membrane-bound nucleus. Kingdom Protoctista: algae, slime molds, etc. Kingdom Fungi: Live on decaying organic matter, mushrooms, mold, mildews. Kingdom Plantae: mosses and vascular plants. Photosynthetic. Kingdom Animalia: multicellular eukaryotes: They ingest organic compounds as their food source. There are at least 24 phyla, then subphyla. Man: Kingdom – anamalia; phylum chordata; subphylum vertebrata; Class Mammalia; Order, Primates, etc. Finally Homo sapiens sapiens (man, wise).

Kingdom:	Monera (Prokaryote)	Protista	Fungi	Plantae	Animalia
Organisms:	Bacteria	Amoebas, diatoms, and other single-celled eukaryotes, and sometimes simple multicellular organisms, such as seaweeds.	Multicellular, filamentous organisms that absorb food	Multicellular organisms that obtain food through photosynthesis	Multicellular organisms that ingest food

Linnaeus’ classification makes sense, but the fact that it changes at the Kingdom level, let alone at lower levels shows that it is not hard and fast. There is no reason why they should be divisible in a perfect way, and there are frequent minor modifications. Why there are no hard and fast rules makes sense later, when we talk about evolution.

Linneaus has another great contribution. That is the now popular concept of referring to a creature by its double name of genus and species. Thus cats, dogs and elephants are felis, canis, and loxodonta, respectively, according to genus. Further division is Felis leo (the lion), Felis domesticus (house cat), Felis tigris, tiger, Felis pardus (leopard). Dogs: Canis lupus (the European gray wolf), Canis familiaris (the dog). This is the same classification scheme that is used to distinguish people!!! Last name is the genus, first is the species! When the animals are organized, we can develop a tree. At the base are the major classifications (e.g., animals and plants) and then it branches out further, first phyla, class, then order, then families, then genera, and finally species.

If every little species is placed on the tree, it has over a million ‘branchlets’. Linneaus never asked, but others posed the question – was the tree formed as is in the beginning of creation, or might not the tree have developed from a small shoot, the different branches growing with time? Linneaus never made this jump. Others must have because he was known to have emphatically denied that his arrangement was to be taken for any indication that one species developed from another. He stated that there were as many species today as there were created originally by God, not one more nor one less. Others must have believed differently, but no one was willing to incur the wrath of making such a statement of such heresy.

What is the problem? That no one has seen a cat change, nor a catfish. If there were changes, it would take hundreds of thousands, perhaps millions of years. And there’s the rub. The age of the Earth was only 6000 years. There simply wasn’t enough time for changes to occur.