Taxonomy (Or Why Modern Biological Categories are Wrong)

cladeAristotle was the first to systematically lay out various living things in the world. According to him, they could be divided into three categories: plants, animals and rational beings (humans). Insofar as biology is concerned, human beings are animals. Therefore, there were two biological categories: plants and animals. Carl Linnaeus extended this knowledge to cover many new kinds of plants and animals, and created more divisions below that of plants and animals. Many of our modern biological categories come from him. The highest division was the kingdom and there were two kingdoms: plants and animals. In 1866, Ernst Haeckel suggested that simple single celled organisms form a third kingdom that he originally called Monera. (He later called this kingdom Protista.) His reasoning behind this change was that biological divisions show historical ancestry (common descent). Modern taxonomists have followed this new pattern and begun a program of categorizing biological things according to ancestry. This is wrong because it is contrary to the purpose of biological categorization.

There are thousands and thousands of different kinds of biological things. There are also many possible ways to categorize them. We might categorize living things by considering how we use them. So weeds refer to plants that we do not want, trees refer to large plants that provide shade, vegetables are edible plants with a similar kind of taste and fruits are plants that have sweet parts. This kind of categorization does not help us understand the living thing. It simply helps us categorize the living thing according to our purposes for it. In fact, any external categorization will not help us understand the living thing. I might name plants according to where they are found, whether I like them, where I bought them or what they can be used for. But these things may vary even if the plant (or animal) stays the same. Furthermore, even if these things do not vary, the explanation for why they do not vary includes knowledge not related to the living thing in question. For example, the reason why pineapples are edible partially has to do with the human digestive system. Finally, even the knowledge about the living thing itself does not unify our knowledge of that living thing. So no externally based categorization scheme is proper if our goal is understanding the living thing itself.

Categorizing living things by their ancestry is an external categorization scheme. The explanation why two living things were placed in the same category would be an external fact (that it is the best fit for those two individuals given the rest of biology). Although historical knowledge is invariant across researchers, it includes both facts about the living thing itself and facts about the rest of the living things that happen to live in the world. Secondly, knowing that dogs and wolves share a common ancestry does not unify our knowledge of dog or wolf biology. Knowing that both dogs and wolves are mammals (and that being mammalian is more fundamental than being a dog or a wolf), does unify our knowledge of either a dog or a wolf.

When we categorize living things we must begin with what is most fundamental, and work our way to what is least fundamental. What is most fundamental to a living thing is the reason why it is alive. Without that, it would not be a living thing at all. Everything else that a living thing does supports the life of that living thing first of all. Least fundamental are the parts of the living thing that can change without harm to that living thing – such as the length of hair, the color of hair or the growth of new branches. Nowhere in this scheme is there room for facts about the ancestry of living things.

The purpose of categorizing living things in biology is to organize them in order to understand them in themselves. The purpose requires categorizing living things according to differences in those living things beginning with the most fundamental differences. Since the differences between living things are purely internal, there is no room for history. Therefore, classification schemes such as cladistics that are based on historical relationships between organisms are universally wrong.

Determining the Most Specific Category

So far I have explained how to divide categories and why categories are important. What I have not discussed is whether there is a lowest category and how to determine it if it exists. There are such lowest categories and they are determined by showing that there is no attribute capable of dividing the category in a fundamental manner.

I will begin by explaining what a lowest category is. In general a lowest category is a category of things that cannot be divided into different kinds of things. These ‘lowest categories’ are called infima species. Specifically, it is a category – such as humanity – that cannot be divided into more specific secondary substances. Humanity cannot be divided by gender, race, origin, or any other means. Traditionally, humans are defined as rational animals. I think that it is more accurate to define humans as rational primates. (Primates include monkeys, apes, orangutans and similar animals.)

Remember that any division of a category must reflect a division in reality. Furthermore, any division must be a further specification of a previous division. So if human beings are divided further, it must be a further specification of rationality. Gender and race are a mixture of cultural and biological attributes. They are not further specifications of rationality. Origin offers no clear difference since it depends on historical attributes (such as born in Germany) or differences that are too specific (such as born to John and Mary). No other traits fail to have these sorts of problems.

In addition, none of these traits offer any fundamental explanatory advantage. Unless we can say that maleness changes everything so that we cannot understand particular human males without consider their maleness, then the trait is not of the right kind to divide that kind. Consider human beings. While maleness is necessary to understand the male hormonal system or the male side of reproduction, it is not necessary to understand male respiration (breathing). Male and female human beings breathe the same. Therefore, gender cannot legitimately divide human beings into more specific secondary substances.

Finally, remember that we are considering secondary substances in these cases. Secondary substances are not the same as attributes. They apply to the thing as a whole, not to some aspects of a thing. So we can only divide secondary substances further if that division explains every aspect of the thing when divided that way. If there is no attribute that divides the substance that way, then the secondary substance is the most specific secondary substance that it is possible to have. It is this that we refer to when we ask what something is.

If we were to consider attributes instead, then we follow the same rules. The ‘thing’ under consideration is now an attribute. We have properly divided it when our division explains every aspect of that attribute so divided. If the division is not necessary to explain every aspect, then the attribute is not divided correctly.

This ends my discussion of language about matter and things. The next area of discussion is change.