Chapter 6 Chapter 1 The Diversity of Life Chapter 4 Macro Taxonomy, Classification Science-1

The most prominent feature of life (phenomena) is its almost infinite diversity. In a sexually reproducing population, no two individuals are exactly alike. In two populations, two species, and two advanced taxa of the same species, And any association... (to infinity) is not the same.Wherever we see uniqueness, uniqueness means diversity. Diversity exists at every level of the biological hierarchy.There are at least 10,000 different macromolecules in an advanced biological organism (some estimates exceed this number).If the state of repression and derepression of all genes in the nucleus is considered, a high-level organism will have tens of millions of different cells, thousands of different organs, glands, muscles, tissues and nerve centers, etc.Any two individuals in a sexually reproducing species differ not only by their genetic uniqueness, but also by differences in sex, age, immune system, and information gathered in open memory programs. Sincerely.This diversity is the basis of ecosystems and is responsible for the phenomena of competition and symbiosis, and drives natural selection.The survival of any organism depends on knowledge of the diversity of its environment and, at a minimum, its ability to cope with it.In short, any biological process or phenomenon is related to diversity.

Of particular importance is the fact that very similar questions about diversity can be asked at each level of the hierarchy, such as the extent or variation of diversity, its mean, its source, function, and its selective value.While diversity is such an important feature in the biological sciences, the answers to most of these questions are qualitative rather than quantitative. No matter what level of diversity is being studied, the obvious first step is to make an inventory.This is to identify and describe the different "kinds" that make up a given class, whether different tissues and organs in anatomy, different normal and abnormal cells and different organelles in cytology, and different organelles in ecology and biogeography. Different taxa and biota, different species and higher taxa in taxonomy.The foundations laid by the descriptions and inventories are the basis for the further development of the relevant science.In the next few chapters I will focus on one component of the diversity of life, the diversity of species of living organisms.

Diversity issues have been a concern since humans began.No matter how ignorant an indigenous tribe may be in other aspects of biology, it has its own vocabulary for the names of the various local flora and fauna.The first creatures to be named are of course directly related to humans, whether it is beasts (bears, wolves), food sources (hares, deer, fish, clams, vegetables, fruits, etc.), clothing sources (skins, fur, feathers), Or flora and fauna with a certain uncanny quality.These are still the main "kinds" in current folklore. When European naturalists returned from their expeditions, they realized that this concern for the diversity of the natural world was all over the world.These naturalists always relish talking about the aboriginal tribes they met and the local birds, fish, plants, and all kinds of strange things in the shallow waters of the sea.These experiences were passed down orally from generation to generation.The people of each tribe are of course only concerned with things in nature that are closely related to their daily lives.Coastal tribes may have known well about the crustaceans of the intertidal zone, but nothing about the habits of the birds of the adjacent forests.Since the species of birds in an area is usually very limited, the local aborigines may have separate names for each species (Di-amond, 1966).If the local plants are lush, the generic name is emphasized. This tradition was continued by Linnaeus.The vocabulary of cultivated plants and domesticated animals is generally richer, but hunting clans or tribes have more knowledge of wild animals and native flora.It is a pity that this knowledge has not been valued by anthropologists for a long time.Due to the influence of the spread of civilization, these traditions are rapidly dying out, so it is too late to study folk taxonomy in many areas.Fortunately, several research works on this aspect have been published in recent years.It is particularly noteworthy that these early classifications not only identified species and varieties, but also sometimes referred to higher taxa.

Early naturalists knew only a limited range of flora and fauna native to their homeland.Aristotle only mentioned 550 kinds of animals, and the herbal annals of the early Renaissance recorded 250-600 kinds of plants.It has been known since ancient times that the same biota does not exist all over the world. Herodotus, Pliny and others recorded this situation according to the travelers' narration.In their writings they mention elephants, giraffes, tigers, and other animals not found on the Mediterranean coast (at least on the European coast). The existence of these novel creatures greatly stimulated the curiosity of Europeans, who were generally amazed by the unknown, whether it was foreign countries, alien people, or flora and fauna they had never seen.Discovering and describing all the rare animals and plants in the world was the long-cherished wish of travelers, editors (from Pliny to Gesner) and followers of Linnaeus at that time.Of course, the ancients knew nothing about the geographic range of the flora and fauna.It wasn't until travelers went deep into Asia (Marco Polo, 1254-1323) or Africa that people gradually became clear about this.When the Portuguese started sailing in the 15th century and after the discovery of the New World by Columbus (1492), awareness of the diversity of the world's biota broke new ground.Kirk's voyage created the conditions for the development of Australia and the Pacific Islands, and at the same time laid the cornerstone of the edifice of biodiversity.However, this was only the beginning, because the specimens of distant animals and plants collected by early travelers and collectors were limited after all.New species of mammals and butterflies were being described even in Europe well into the 1940s and 1950s.

And with regard to the less noteworthy species and less accessible regions, the treasure-trove of undescribed species appears to be exceedingly rich and inexhaustible.Even now we only know about one-tenth or two of the extant species in the tropics. Awareness of biodiversity has grown along with the apparent change in attitudes.Early travelers were just for the curious.What they are most proud of is coming home and talking about all kinds of strange monsters and weird things.This attitude was soon replaced by a fad for purely foreign novelties.Private collectors in Britain, France, Holland and Germany have established museum showcases one after another.Their attitude was not much higher than that of philatelists and coin collectors, but true naturalists such as Linnaeus and Artedi benefited greatly from the zealous activities of these collectors and patrons.In addition, Marcgrave and Rumphius made important contributions to natural history in previously almost unknown areas of Brazil and the East Indies, respectively (Stresemann, 1975).

The 18th century was the beginning of the famous age of sailing. Bougainville and other French expeditions, Cook and other British expeditions brought back large numbers of exotic specimens from overseas.This activity was further expanded in the 19th century with the participation of Russia and the United States.Travelers went to all corners of the world to collect natural history specimens of such a variety that they filled private museum collections, necessitating the establishment of larger national or metropolitan museums and herbaria.These specimens are never considered redundant, as each collection discovers rare species never before seen.In the 1920s and 1930s, there was a well-known expedition team named Bird. In only one expedition (Whitney South China Sea Expedition), they traveled almost all the islands in the South China Sea and discovered more than 30 new species.

The work of Humbert and Bonpland in South America, Darwin in the Beagle (1831-1836), Wallace in the East Indies (1854-1862), and Bates and Spruce in the Amazon Basin are all well-known, but generally Forget about hundreds of other collectors.Linnaeus sent his students to collect foreign plant specimens, and some of the best students died of tropical diseases: such as Bartsch (died in 1738, imitated below), Ternstrom (1746), Hasselquist (1752), Lo-efling ( 1756), Forskal (1763).The situation in the East Indies was an even greater tragedy, where the best of European zoology died of tropical diseases or were killed during a 30-year expedition: Kuhl (1821), Van Hasselt (1823), Boie (1827), Macklot (1832), Van Oort (1834), Horner (1838), Forsten (1843), Schwaner (1851).They all gave their lives to advance the understanding of tropical animal life.Among them Kuhl and Boie are the best young naturalists in Germany (Stresemann, 1975).The gap left by their deaths caused the subsequent decline of German natural history for a while, because geniuses were, after all, rare in a certain period.

Unexplored or little-known areas are just one of the areas that diversity scholars have turned to.Other types of organisms and exotic environments are also objects of study.For example, parasites are worthy of study.Human intestinal parasites have been mentioned as early as 1500 BC in the Ebers Papyrus and by ancient Greek physicians.These parasites were later found to be ubiquitous in both humans and animals, and they were thought to arise naturally.It was not until the nineteenth century that it was recognized that many, if not all, parasites inhabit only one type of host and that a host can be simultaneously infected by several different parasites: tapeworms, trematodes, nematodes, blood parasites, cell parasite.This work, pioneered by the zoologists Rudolphi, Leuckart et al., was then followed by a number of parasitologists specializing in this type of diversity.Due to the complex life history of most parasites, special patience and dexterity are required to study them.

Since parasites can cause serious human diseases (such as malaria, sleeping sickness, schistosomiasis, rickettsia, etc.), special attention is paid to research in this area.Plants are also infested with parasites (e.g. galls, mites; various fungi and viruses).Perhaps it is no exaggeration to say that there are more types of plant parasites than higher plants themselves.Gradually they were found to greatly expand the range of biodiversity. Another area of ​​urgent need for diversity research is in freshwater waters and oceans.Aristotle had a keen interest in marine life when he lived on the island of Lesbos.However, as late as 1758, Linnaeus rarely mentioned marine life in his "Natural System" except for a few fish, molluscs and corals.Since Pallas, S. This quickly changed with the work of Muller and many other Nordic scholars, one discovery after another. Sars was the first scholar who opened the door to deep-sea animals, and his research was highly valued by the British Challenger Expedition (1872-1876).Subsequent ocean expeditions were organized in Scandinavia, the Netherlands, France and Germany, and experts were still busy describing their new discoveries.Marine life itself has also developed a new field of study: marine parasites.Some marine organisms are parasitized by the same parasites as terrestrial organisms (tapeworms, trematodes), but there are others that are restricted to the sea (mesozoans, parasitic copepods, rootheads).

Microscopes have opened up another realm of diversity: the biological world that is invisible, or at least not clearly, to the naked eye.Simple lenses have been used in ancient times to magnify small objects.The combined lens—that is, the microscope—was first successfully manufactured by Dutch manufacturers in the early 17th century. A research report on bees published in Rome in 1625 was carried out by the Italian Francisco Stelluti using a five-fold magnifying microscope. This is the first research work of biological microscopy. For the next two hundred years, very simple microscopes were used, mainly for the study of plant tissues (Hook, Grew, Malpighi) or for the study of minute details of animals. Structures, especially those of insects (Malpighi, Swammerdam). Motes (Daphnia) were discovered by Swammerdam in 1669, but not described in detail, nor continued to study other plankton (Schierbeek, 1967, Nordenskiold, 1928).

Equally important to these developments were historic advances in cytology and morphology of animals and plants.Leeuwenhoek took the diverse field of research one step further with the microscope.He is said to be able to magnify 270 times using a single-lens microscope.Since 1674, he has discovered protozoa (protozoa and unicellular algae) and other plankton (rotifers, planktonic crustaceans, etc.) in successive years, which later developed into the most active biology. The discipline lays the foundation.He even discovered and described bacteria.The fact that he discovered single-celled animals and plants had a huge impact on the theory of spontaneous generation and the thought circle at that time.Arguably Leeuwenhoek's most important feat was that he first made biologists aware of the vastness of the microbial world and posed entirely new questions to taxonomists. It was not until 1838 that Ehrenberg made a comprehensive discussion of protozoa for the first time, but this was before the cell theory was proposed. He regarded protozoa as a "complete organism" and endowed it with the same various organs (nerves, muscles, etc.) as higher organisms. , gut, gonads, etc.). 1848 C． T． von Siebold formulated the phylum Protozoa and specified its unicellular nature. In the first half of the 19th century, rapid progress was also made in the research of various zooplankton and algae.In short; every improvement in the microscope has brought our knowledge a step further, and the invention of the electron microscope in the 1930s allowed us to study even the morphology of viruses. The focus of what I have introduced so far has been on the diversity of animals, opening the curtain on the vast world of diversity.The same is true for the development of the plant world, where a series of fields are yet to be explored.Even before phagocytic plants (angiosperms) were fully described, some botanists had begun to specialize in the study of cryptogamic plants (ferns, mosses, lichens, algae) and a wide variety of fungi (Magdefrau, 1973). This is not the end of the matter!In addition to the diversity of the present world, there is also the diversity of life in the past era represented by fossils.According to the highest estimate, there are about 10 million species of animals and plants in existence.Considering that life on Earth began about 3.5 billion years ago, and that a relatively lush biota is estimated to have existed for 500 million years, while also acknowledging that the species composition of the biota has its reasonable turnover, it is estimated that at least 100 million an extinct species.The era of great discoveries in paleontology Fossils, such as the discovery of Archaeopteryx, the transition between reptiles and birds, and the discovery of ichthyostega, the transition between fish and amphibians, may be coming to an end, yet still remains today Occasionally, new phyla of fossil invertebrates are discovered. It seems that the discovery of new orders, new species, and new genera is far from the end. The discovery of fossil plants and animals has a long history, dating back to ancient times (see Part II). Heradotus, Strabo, Plutarch, and especially Xenophan-es all mention fossilized molluscs as a result of the degradation of marine life.But fossil mammals, reptiles, and amphibians were not noticed until the seventeenth century, and new discoveries increased in the eighteenth and nineteenth centuries.The discoveries of mastodons, dinosaurs, ichthyosaurs, pterodactyls, ornithosaurs, and other large fossil mammals were sensational. Paleobotany also broadened people's horizons (Magdefrau, 1973: 231-251).Since it is difficult to piece together fossil stems, leaves, flowers, pollen, and fruits (seeds), research work in this area is problematic. Fortunately, the number of well-studied fossil plants has gradually increased, and their spatial and temporal The distribution on is also known more. The contribution of the Fossil Pollen Institute is particularly important in this respect.But there are still many puzzles to be solved, including the origin of angiosperms. The oldest known fossil until the 1950s (Late Precambrian) is about 625 million years old.Later, Barghoorn, Cloud, and Schopf discovered fossil protists in rocks with an age of about 3.5 billion years, which pushed back the age of the oldest fossils by about five times. Prokaryotes, both living and fossil, are currently the most urgently developed field in de-scriptive systematics.Intensive studies of bacterial biochemistry and physiology have revealed that they are more diverse than originally thought. Woese and his collaborators even proposed a separate kingdom (king-dom) for methane bacteria and related bacteria, which they called Archaebacteria.In addition, a separate realm is established for those protists that are considered to constitute the symbiotic organelles (such as mitochondria, plastids, etc.) of eukaryotes.Studies of ribosomal RNA and other molecules finally shed light on the previously controversial question of bacterial taxonomy (Fox et al., 198O).It is quite interesting that there is always something new, often startling, in taxonomy, the oldest branch of biology, such as the rediscovery of the genus Trichoplax, which was thought to be an epigenetic The most primitive of animals (Grell, 1972). When looking back at the history of biodiversity research, one cannot help feeling that diversity is aggressive in the face of: Space: continents of the world, Time: from 3.5 billion years ago to the present; Size: from viruses to whales; Habitat: air, land, freshwater, ocean; Lifestyle: independent living and parasitic.Naturally, one cannot ignore the extraordinary abundance of life phenomena in its surroundings, and in fact there are various reasons to study it.The first is man's constant curiosity about his surroundings, and his striving to know it, to understand it.In addition, it is also necessary to know which plants and animals are useful for practical purposes, especially as food or for medicinal purposes.When Linnaeus was asked what is the use of studying diversity, as a creationist, he replied: What is the use?Everything created has a purpose, some plants are used for medicine, some creatures are used for food, etc.Everything created by the Omniscient, Almighty Creator has a specific purpose, or benefit to someone or something else.It is our task to reveal these intended uses or benefits, which is the purpose of natural history. Certain scholars of the seventeenth and eighteenth centuries were interested in studying nature for another reason.The Greeks had long celebrated the harmony of nature: the whole world formed Kosmos (the word Kosmos for the Greeks meant beauty and order).Whether the natural world is regarded as the perfect creation of the creator, or regarded as equal to God by the Roman philosopher Seneca and the pantheists, many devout scientists, such as John Ray, Newton, Linnaeus, etc., believed that the natural world has a deep There is a deep hidden order and harmony, and it is their task to reveal and explain it. The laws of physics emphasize universality and consistency.Thus the natural scientists of the 17th and early 18th centuries believed that if only chance and the unforeseen blind action of the laws of physics were at work in the universe, there would be nothing but perfect uniformity or total chaos in the world.It thus appears that only the existence of a Creator can account for the actual and appropriate biological diversity.Newton once said: "We can only know him (God) by his supreme wisdom and wonderful design of things and the final cause; praise him because of his perfection; respect and worship him because of his authority; we are Worship him as his servant; God without authority, without wisdom, and ultimate cause is not God but only fate and nature. Blind metaphysical necessity (which must be the same at all times and places) cannot produce diversity. nature. The diversity of nature that we find, suitable for different times and places, can only come from the mind and will of a God who must exist." Therefore, the study of the absolute harmony and diversity of nature is the shortest way to know God.This became the fashion of natural theology in the eighteenth and early nineteenth centuries.Not only adaptation (which is evidence of design) but diversity itself is a theme of natural theology.No one else was more acutely aware of this than Agassiz, who considered natural systems to be the key evidence for the existence of God and articulated this view in his book Essays on Classification. The variety of biological organisms is almost unimaginable, which is also a challenge to human intelligence.Since the scientific revolution, the western world has devoted itself to discovering the laws of mechanics and physics.Yet the diversity of life has not succumbed to this trend.If we want to discover such a law, we can only sort out the diversity by means of classification.This is why naturalists in the seventeenth, eighteenth, and nineteenth centuries were keen on classification.Taxonomy, at a minimum, can bring order to a dizzying variety.Classification does eventually lead to the search for laws: descent from a common ancestor (modified).Such ordering procedures seem to have been so important to eighteenth-century zoologists and botanists that classification was then considered almost synonymous with science. Like other branches of science, taxonomy has its share of geniuses and dummies.There are some specialists who spend their lives doing nothing but describing new species.This is beyond reproach in the Linnaeus era when taxonomy was famous.At that time, other aspects of biology were neglected due to the dominance of systematics.But then, quite reasonably, the question was raised: Can such a mere description, which neither seeks laws nor seeks generalizations, qualify as science?From the 1730s to the 1750s, the brilliant achievements of von Baer, ​​Magendie, Claude Bernard, Schleiden, and von Helmholtz in other fields of biology caused the reputation of systematics to decline rapidly. But after 1859, systematics revived when Darwin's theory of common ancestors provided the first non-supernatural justification for the existence of higher taxa.However, this new pulse soon faltered, and the exciting advances in functional biology in the last third of the nineteenth century brought systematics into decline again.Physiologists and experimental embryologists believe that systematics is a purely descriptive work, not worthy of the attention of "true scientists".Physical scientists and experimental biologists agreed that natural history was just another way of collecting stamps.A famous zoologist once said when visiting Cambridge University in the late 19th century: "Natural history is kept down as much as possible, and is regarded as a boring chore by many mathematicians at this revered university." In 1960, a The noted historian of the physical sciences also said: "Taxonomy does not appeal to historians of science at all." These nitpicking critics simply do not understand that the study of diversity is to a large extent the basis of research in every major branch of biology (Mayr, 1974b).Nor do they know what Aristotle, Cuvier, Weissmann, or Lorenz achieved with diversity.Natural history is the richest and most original branch of biology.Wasn't Darwin's work basically based on the study of natural history?Aren't ethology and ecology developed from natural history?If biology were confined to laboratory research, cut off from natural history to obtain constant nourishment, it would be a very narrow and poor science. Unfortunately, no one has yet written a history of the influence of natural history on the development of biology, although D. E． Allen's The Natu-ralist in Britain (1976) is an excellent exposition of nineteenth-century Britain, and Stresemann's Ornithology (1975) is The same thesis was expounded on birds.In every group of naturalists there are brighter and curious minds who ask deeper questions of all kinds.They made important contributions to some of the most valuable treatises in natural theology (eg Ray, Zorn, Kirby).They founded journals and societies, and they outlined fundamental questions that eventually became major topics in evolutionary biology, biogeography, ecology, and behavior.Interestingly enough, all the advanced people in this area are amateurs -- enthusiastic, dedicated amateurs.Natural history is the last of the various disciplines of biology to be professionalized.It is only in the modern era that the conceptually important contribution of natural history to biology has been recognized. There is no shortage of so-called histories of taxonomy, but they are invariably just histories of classification.These histories chronicle the gradual refinement (and occasional regression) of specific classifications of plants and animals from the time of Aristotle until the end of the nineteenth century.These historians point to the relentless efforts of scientists to repeatedly reclassify the genera, families, and orders of organisms in order to establish a more uniform classification system, that is, a classification system that reflects common ancestry and evolutionary divergence. A fascinating history of trial and error. A history of the kind described above, while paying close attention to classifications, does not deal seriously with the conceptual changes involved.The most important aspects of the history of systematics, like the history of evolutionary biology, are conceptual rather than factual, and certain competing (if not outright antagonistic) concepts have existed side by side from the early eighteenth century to the present Up to 250 years.Part of the reason for the inconsistency in conceptualization in taxonomy is that there are different traditions in the taxonomy of each group of organisms.This is true not only for bacteria, animals, plants, but also for different types of plants, insects or mammals.Some new concepts such as multi-character classification, polytypic species, sister species (as opposed to biological clan), or biological species, etc. have been introduced into the taxonomy of advanced taxa at different times. One's first impression is that the history of systematics is one of never-ending struggle with the same old problems. These old questions are: What is a species?What is kinship?How are higher taxa best distinguished?How to group species into higher taxa?What are the most dependable traits?On what basis should species be arranged in higher categories?What is the function of classification?etc. It is clear that the history of systematics is completely inconsistent with the conception of scientific development articulated by Thomas Kuhn.Even the Darwinian Revolution of 1859 did not have the decisive impact on systematics as one might expect.The reasons for this state of affairs will be described in later chapters.It should also be mentioned here, however, that concepts have by no means remained static over the past 300 years.Concepts have changed and been clarified, as is well demonstrated by changes in the usage and meaning of some frequently used terms over time and by different scholars. As long as the following series of conditions exist, how can the unified theory of systematics develop? The word "affinity" can denote both mere similarity and genetic relationship; the word "variety" can be used to denote geographically isolated populations as well as variations within a species (individuals). ); "species" can refer to individuals with different shapes, but also to reproductively isolated populations; "classification" can be used to refer to identification schemes, and can also be used to refer to true classification.In addition, "natural system" has very different meanings in different periods, and some terms, such as "category", are often used by the same scholar to express very different concepts.Most scholars who use the same term (e.g., class, variety) to mean different things are not aware of their confusion at all.It may be true to say that much more progress has been made in clarifying taxonomic concepts in the past 40 years than in the previous two centuries. When we see elephants, giraffes, penguins, swallowtails, oak trees and mushrooms, the first striking impression we get is that of uniqueness.As mentioned earlier, uniqueness means diversity.If this diversity were really chaotic, it would be impossible to study it.Yet there are regularities, and as Darwin and many others have pointed out, these regularities can be explained.There are identifiable causes of diversity as well as factors of chance.It is therefore natural to admit that systematics is a science.The theme it studies is diversity.Simpson (1961) defined it as: "The study of systematics is the kind and diversity of biological organisms and all the relationships between them." He later further pointed out that systematics "is the most basic and extensive part of (biology); the most basic is that (organisms) can only be studied and dealt with scientifically after a certain taxonomy is established, The broadest scope is because all known knowledge about (organisms), including morphology, physiology, psychology, and ecology, is gathered, used, and generalized in various branches of (systematics), and is used for it. Provide research tools." Because systematics involves such a wide range of fields, scholars have tried to subdivide it.For example, it has been argued that the classification of a taxon has gone through different stages of development. "These stages of development are sometimes referred to informally as A, B, Y taxonomy. A taxonomy refers to the taxonomic level at which species are identified and named; B taxonomy refers to the arrangement of these species in the appropriate taxonomic order Middle, lower, and higher order elements make up natural systems, Y taxonomy refers to the study of evolution in terms of classification" (Mayr, Linslcy, and Usinger, 1953: 19).Actually A and B level work is done concurrently (they are not really phases) and Y taxonomy is not strictly a taxonomy.The history of taxonomy is best understood if it is subdivided into two categories: (1) microtaxonomy, the study of methods and principles for identifying and differentiating groups (species) of organisms, and (2) macroscopic taxonomy. Taxonomy (macrotaxonomy), the study of the methods and principles of the classification of species of organisms (that is, the arrangement of species in a classification system).Thus, taxonomy as a whole (narrower than systematics) is defined as "the theory and practice of distinguishing and classifying species of organisms" (Simpson, 1961; Mayr, 1969). When it comes to diversity, it has to be categorized.Thus there is the classification of languages, the classification of goods by manufacturers or markets, the classification of books in libraries, or the classification of plants and animals in nature.Classification (process) in the above case is the grouping of individual things into classes.There is no dispute over this basic procedure, what has been debated over the past few hundred years is: what is the best way to divide?What classification criteria (basis) should be used?What is the ultimate purpose of classification?The task of the history of macrotaxonomy is to enumerate and discuss in turn the various and often changing answers to these questions. Before addressing this task historically it is necessary to discuss critically certain concepts that have often, if not always, been confused in the history of taxonomy. Identification schemes are not classifications.Deductive reasoning is the basis of the identification process.The purpose of identification is to place the individual under study into a phylum within an existing taxonomic system.If successful, the specimen is authenticated.Identification involves only a small number of traits, which determine the position of the specimen in the key (Mayr, 1969: 4, 66, 112-115).Corresponding to this, according to the current understanding, classification is to group populations and taxa into classes, and then group these classes into larger classes in turn.Classification utilizes many traits. Understanding the distinction between classification and identification is crucial in evaluating so-called "special purpose classifications", such as the "classification" of medicinal plants according to their specific therapeutic properties.Such "classifications" are really nothing more than identification schemes (as far as modern taxonomists are concerned).Dioscorides, a doctor in ancient Greece, divided (classified) plants according to their medical functions, in order to find the right medicine and choose the right plants to ensure safety and curative effect.Since most medicines have come from plants almost until now, pharmacopoeias are at the same time handbooks of botanical identification. Some special purpose classifications, however, are not keys but actually serve a purpose assigned by name; this is the case, for example, in the ecology literature where plants are classified according to their habitat or growth form.Such classifications are of limited use, yet virtually all "classifications" before the sixteenth century were of this utilitarian nature.Therefore, when considering classification, it is very important to be clear about the various possible purposes of a classification. Philosophers and taxonomists have recognized almost from the beginning that classifications have a dual role, one practical and the other general (that is, scientific or metaphysical).But there are different views on the nature of these two roles.A practical use not emphasized by earlier scholars was the use of classifications as keys.Most often emphasized in recent years is the classification as an index of information storage and information retrieval systems.To maximize this effect, classifications should consist of subject subjects with the greatest number of common properties.This classification automatically becomes the key to the information stored therein. 易于检索一般是这样一些分类的主要或唯一目的，例如图书馆的图书和其它或多或少按任意标准归类的非生物体。与此对映，对于与原因联系的项目（例如疾病分类）或与起源有关的项目（如生物分类）的分类则受到某些限制，然而仍然具有可以作为影响深远的概括的基础的能力。 就生物学分类的一般作用（意义）来说，随着时间的不同发生了很大变化。就亚里斯多德而言，它反映了自然界的和谐，特别是表述在《自然界阶梯》中。就自然神学家来说，就正像阿伽西所明确表示的那样，分类论证了世界设计师（造物主）的创造方案。 自然系统就是这方案的表现。在达尔文提出了共同祖先学说以后，分类的形而上学解释就让位于科学解释。由于生物学中的各种比较学科的观察研究都是借助于“自然系统” （现在已按进化论观点下定义）组织进行，所以分类的主要功能就是区分分类单位并建立高级分类单位等级结构以便作出最大数量的正确概括。这种分类的根据是，假定某一分类单位的几个成员，作为后裔从一共同祖先处各自分享了一份共同遗产，它们彼此之间较之没有这种关系的物种将会有更多的共同性状。因而进化论观点的分类在一切比较研究中具有相当大的启发意义。这种分类随时要接受更多性状的检验，或者是通过与其它分类进行比较来检验。 生物学分类具有这两种（实际的和一般的）作用或目的就引起了争议。例如，信息检索的目的和概括的目的是否互不矛盾？分类所包涵的概括的本质是什么？这些概括能否看作是学说？ 对分类各种作用有关问题的上述简单介绍可以使读者在追踪对这些问题的态度历史性变化时提高辨别力。 4．1亚里斯多德 分类学的历史要从亚里斯多德（公元前384－322）开始写起。虽然在他以前人们对动植物已知道得不少，但流传下来的早期着作中根本没有分类的知识。就实际知识而言，亚里斯多德显然把他从前人所能得到的（很可能绝大多数是从希波克拉底学派得到的）都写进了他的着作中。但是亚里斯多德对某些海洋动物的细节描写得如此逼真，这就表明这些知识都是第一手的，至少也是他亲自从渔民或“民间”来源得到的。一般认为他在勒斯波斯岛居住时专心致志于博物学研究。他在叙述性动物学方面的主要着作是《动物历史》（Historia animalium），但是在《动物解剖》（De partibus）和《动物繁殖》（De generatione）中以及其它着作中都有很多关于分类的论述。 传统上一般都把亚里斯多德视为分类科学之父，但是从文艺复兴一直到现代对他的真正分类原则是什么都有怀疑和分歧意见。这看来部分原因是由于亚里斯多德在他早期的着作（在其中他提出了他的逻辑学原理）和他后来的生物学着作中采用了不同的方法，另一部分原因是他认为按逻辑区分下定义的方法不可能为动物提供合理的完整描述和表明动物类别的特征。 亚里斯多德的逻辑方法最好是用众人皆知的室内游戏来说明。一位客人被引进室内让他猜他不在室内时其它人选定的一样东西。他提出的第一个问题可能是“它是活的吗？”。这样就把他所想像的东西分成了两类：生物与非生物。如果答案是“对”，他就可以问：“它是动物吗？”这样就将活的生物又分成了动物与非动物两类。由此，总是把剩下的东西的类别分成两个部分（一分法，dichotomous division）的方式继续下去他迟早就会猜中。 用亚里斯多德的逻辑（即形式逻辑）来表示，最大的类别，“总类”（例如植物），按演绎法分成两个（或多于两个）其下属的亚类，称为“种”。每个“种”在下一轮较低级的划分中成为“属”，“属”再细分为“种”。如此反复继续进行，直到最低级的种不能再分为止。当然，逻辑学家的“种”和生物种勿须有关，虽然在划分生物的种类时最后一步的结果可能事实上就是生物种。按逻辑分法的分类称为下行分类（downwardclassifi-cation），它既适用于无生物（如家具可分为椅，桌，床等等），也适用于生物。 使后来的学者感到伤脑筋的是当亚里斯多德在阐述他的逻辑方法时实际上是将之作为应用于动物的区分依据（标准）的例子，诸如“有毛或无毛”，“有血或无血”，“四支脚或非四支脚的。”但是，逻辑的分法并不是亚里斯多德用于动物分类的方法，这可以从亚里斯多德的动物系统并不是一个细致复杂的等级结构这个事实看出，特别是他还特地嘲笑了把二分法作为分类原则的作法（De partibus animalium 642b5一644all）并进一步指出为什么这样做不行。尽管亚里斯多德并不采用它，但是从文艺复兴（Cesalpino）到林奈（见下）的生物分类中，逻辑分类法一直是优先被采用的方法。 和大多数历史文献所记载的正相反，我认为将这种分类方法强加在亚里斯多德身上是没有道理的。 那么亚里斯多德是怎样为形形色色的动物分类的呢？他是按非常现代化的方式进行的：他通过观察将动物分成类：“正确的办法是按类来了解动物，按照大多数人的方式，他们是根据很多特点而不是按二分法来分类”。（643b9—14）。“是根据身体的各部分，或整个身体的形状相似性将各个类彼此分别开”（644b7－9）。只是在他确立了类之后，亚里斯多德才选用一些方便的鉴别性状。在这个常识性的表现性状的方法上亚里斯多德又加上了一个评价可以表示这些类（别）特征的性状系统并按某种序列将这些性状排列起来。亚里斯多德分类学中的这种排列是现代学者最难于理解的。大家都知道，亚里斯多德对四种元素——火，水，土，空气——的重要性非常重视。因此，性状热与冷，或潮湿与干燥对他来说至关重要。他把热排在冷之上，潮湿排在干燥之上。血液既热又潮湿，因而成了特别重要的性状。结果，亚里斯多德对不同的生理功能就有一个价值尺度，因为生理功能似乎也是不同种类动物的性状。比较热又比较潮湿的动物被认为是有理性的；而较冷、较干燥的动物会有较少的与生命有关的热，就缺少较高级的“灵魂”。这种形式的臆测特别适合文艺复兴时代亚里斯多德学派的口味，并促使他们按设想的生理重要性提出了分类学性状的具体等级尺度。 如果要理解为什么亚里斯多德的分类并不就是鉴定方案或纯粹的表现性状方案，上述这一点必须记牢。亚里斯多德之所以辨别动物的某些类别主要是为了解释他的生理学说并且能将关于生殖，生活史（后代的完善程度）和生活环境（空中、陆地、水域）的有关知识组织起来。因此就他的意图来说，把水生的鲸和陆地的哺乳动物分开，将软体自由游动的头足类同海洋、陆地的硬壳软体动物分开，就是十分合理的。尽管有某些不合适的组合以及一些剩下来未分类的动物，但就整体而论亚里斯多德的动物高级分类单位显然优于林奈的，后者主要兴趣在于植物。 在研究亚里斯多德的动物学着作时，有三点予人印象最深。首先，亚里斯多德对世界的多样性具有特别浓厚的兴趣。其次，并没有证据表明他对动物分类本身特别感兴趣，他也从来没有在任何地方将他所识别的九个高级分类单位列表加以说明。第三，再重复一遍，他的分类并不是逻辑分类的结果。特别值得注意的是，亚里斯多德的逻辑体系在《动物的历史》中反映得非常之少。在他的着作中人们感受最深的是一种经验式的、几乎是实用主义的方法而不是演绎的逻辑方法。 亚里斯多德仅仅是想通过最有效的途径告诉人们他对动物的了解以便“我们对明显的性状和共同的性质首先有一个明确的概念”（491a8）。达到这一目的的最简捷有效的途径是比较。的确，《动物解剖》全书就是在比较的基础上编写成的：结构的比较（比较解剖学），生殖生物学以及行为学（动物心理学）的比较。为了便于比较他将所提到的580种动物归类成群，如鸟、鱼，而且往往是运用像希腊文字一样古老的类、群。 他将动物分类成“有血的”和“无血的”，这种分类一直被人们接受直到拉马克将之改名为“脊椎动物”与“无脊椎动物”为止。在有血动物中，亚里斯多德将鸟和鱼分为不同的属，但是对其余的动物就遇到了一些麻烦。他认为胎生或卵生是重要性状，就将有毛的胎生动物（现在称为哺乳动物）和冷血的卵生动物（爬虫类和两栖类）分开。 他明确地将鲸从鱼和陆地的哺乳动物区别开来。他还把不同的飞翔动物如羽毛翼的鸟，皮革翼的蝙蝠和膜翼的昆虫彼此远远地分开。但是在无脊椎动物中他的介壳类（甲壳软体动物）却包括藤壶，海胆，蜗牛和蚝等等杂七杂八的东西。 亚里斯多德对好几类动物的结构差异，特别是消化系统和生殖系统，提供了丰富的观察资料。然而他似乎对动物生态学（它们的生境和生活方式），生殖生物学以及动物的气质也同样有兴趣。“各种动物在其生活方式，活动、习惯与才能上都有所不同”，特别是在和水、空气与陆地的关系上（487all－12）。现在已经清楚亚里斯多德并不是为了便于鉴定而提出动物的分类。 那么亚里斯多德在系统学历史上的重要意义究竟是什么？他的最重要贡献可能是他，一位卓越的哲学家，对动物及其性质如此感兴趣。这就大大有利于动物学在中世纪末期和文艺复兴中复苏。无论是在动物结构、食性、行为，还是生殖方面他都提出了意义重大的问题从而使对动物的研究成为一门科学。他还为后来生物学分成形态学，系统学，生理学，胚胎学以及行为学奠定了基础。此外，他还教导研究人员应当怎样进行工作。 他将个别的种类（种）和集合的类（属）加以区分并使之定型化也成为后来更细致更透彻的分类的转辙点。 亚里斯多德现在已不再被认为仅仅是经院哲学之父而且也是一位哲学化了的生物学家，他的着作在很多方面都投射出了新的光芒。但是对他的分类学概念结构还缺乏现代的分析。 作为广泛的概括也许可以说自从亚里斯多德辞世以后博物学的水平一直是江河日下。 Pliny与Aelian都是忙忙碌碌的编纂家，他们不加批判地将优秀的博物学和荒诞的神话传说揉合在一起。在随后的年代里撰写动物不是为了提供关于动物的知识而是为了说教；动物成了象征。如果为了将勤恳道德化，就写蚂蚁；为了赋予勇敢以道德意义就写狮子。 随着基督教兴起，关于动物的故事往往成为宗教小册子中的一部分。动物还成为基督教教义中某种思想概念的象征或标志，并被引进到油画和其它艺术中去。可以说研究动物成为一种纯粹精神性的或美学的活动，几乎完全脱离了博物学。广泛的来说，情况就是这样，最低限度从Pliny（死于公元后79年）到十五世纪这一千多年中就是如此（Stannard，1979）。FrederickⅡ的《猎鹰训练术》（1250年）以及AlbevtusMagnus（约1200－1280年）的着作却是突出的例外。 在随后的几个世纪中情况发生了迅速的变化，一些事态的发展更加速了这种变化。 其中之一是重新发现了亚里斯多德的生物学着作以及这些着作的新译本问世。另一个是生活水平的普遍提高以及随之而来的对医疗技术与相应的医用植物的更加重视。最后，一种“回到自然”的运动，放弃片面地追求精神生活，在中世纪后期兴起。从Hildegard von Bingen（1098－1179年）以及Albevtus Magnus以后，越来越多的人都到野外观赏活的动植物，而且还编写关于动植物的书。随着印刷术的进步，这一类的书也就印刷出版了开来。但是这是一个迟缓的渐进过程。着名而又缺乏批判性的编纂家Pliny的百科全书式的传统一直延续到Gesner和Aldrovandi的时代。但是，在十六世纪时，一切关于自然的书都是由医生写的。