The most commonly used biological classification system is based upon that of Linnaeus' Systema Natura, first published in 1735. Linnaeus believed he was discovering the system of order that existed in God's mind during the creation. Today, the modified scheme can be viewed as a listing of our close and distant kin. The classification attempts to be phylogenetic in that at every level in its hierarchical structure, it is supposed to be grouping organisms that have common ancestors. The taxonomy represents phylogeny: evolution.
Resemblance's often indicate relationships. That is a principle we use every day. Although we live in different places, every once in a while I am somewhere with one or both of my two sisters. They are both older than I am, and we don't (in our opinion) look much alike. Yet whenever we go some place together, some stranger will state "you two (or three) must be sisters!" What they are assuming is that the physical similarities between the three of us are so great that it must indicate common ancestry. The three of us share certain physical traits because we share the genes that cause these traits. Like everyone else, we got our genes from our ancestors. Since we have so many traits in common, it is likely that our common ancestors are not too far back in the past, as indeed they are not: our parents.
Evolution, phylogeny, is based on the same principle. Similar physical structures that are due to common genes and common ancestors are referred to as homologous structures, or homologies. The wings of birds, the foreleg of a horse, and the arm of a human are examples of homologous structures. If you examine the skeletons of the three animals the similarities increase, and indeed much of the DNA involving these structures is identical.
Some structural similarities may occur in animals that are not due to common genes, but are the result of adaptation to similar function. These structures are referred to in biology as analogous structures, or analogies. The classic example of analogies is the wing of a bird, a bat, and a butterfly. There are resemblance's between all three structures due to the common function, but in fact each evolved separately and are not genetically similar.
Increasingly, it is possible to use direct DNA comparison between two structurally similar animals to determine if their similarities are indeed homologies. The more common ancestors two organisms have, the more nearly identical their DNA will be. In areas where DNA comparison has been done it has validated the taxonomic system as a listing of our close and distant relatives.
The biological classification system is a nested hierarchy. Each grouping contains other smaller groupings within it, all based on homologous traits. There are seven basic levels of classification. From largest to smallest, they are:
KINGDOM
PHYLUM
CLASS
ORDER
FAMILY
GENUS
SPECIES
Further divisions are possible since each grouping above can be further subdivided by use of the prefix SUPER, SUB, and INFRA, as in Subphylum, Infraorder, and Superfamily. In addition, Subfamilies may be subdivided into Tribes. In the following table, you can see how modern humans are classified in regard to the major categories. The table provides the most recent classification; the classification of humans and certain of the apes in the same Family and Subfamily is a recent trend based upon the enormous DNA resemblances between the two groups, and has not been adapted by all classifiers. [Though you text does not provide you with the complete classification of humans, it does use the correct term for our Tribe of Hominini, or hominins. However, on p. 40, the definition provided of the term hominin is correct within the text, but INCORRECT in the blue definition box at the bottom of the page. Hominin is a term that refers only to modern humans and the closely related fossil species that were clearly bipedal or evolving bipeds. Chimps and gorillas, as well as the bonobo, (and their immediate ancestors) are members of the Panini Tribe, or panins; NOT hominins. Also, you text is INCORRECT in its constant reference to Homo sapiens sapiens. The second "sapiens" is an old subspecies name that is NOT used by physical anthropologists and biologists today, since there have been no subspecies within our species since it evolved approximately 200,000 years ago. We are all Homo sapiens.]
| Taxon | Name | Traits | Members |
|---|---|---|---|
| Kingdom | Anamalia | Incapable of photosynthesis; must consume plants or other animals; mobile. | Insects, sponges, starfish, worms, shellfish, birds, fish, reptiles, cats, dogs, etc. |
| Phylum | Chordata | Internal skeleton; notochord (cartilaginous); dorsal nervous system | Turnicates, fish, birds, reptiles, pigs, amphibians, cats,dogs, etc |
| Subphylum | Vertebrata | True vertebral column/ bony spine | Fish,birds, reptiles, amphibians, pigs,cats,dogs,etc. |
| Class | Mammalia | warm blooded: reproductive efficiency; mammary glands; fur or hair | Pigs,cats,dogs,cows, horses, deer, bats,rodents, whales, monkeys,apes, etc. |
| Order | Primates | Hands specialized for grasping; specialized vision; large brains for body size | Lemurs, lorises, tarsiers, monkeys, apes, humans |
| Suborder | Anthropoidea | No moist nose; poorer sense of smell; similar senses; larger brains for body size | Monkeys (both Old and New World), Apes, Humans |
| Infraorder | Catarrhini | Down turned nose; 32 teeth; well developed thumb | Old World Monkeys; Apes, Humans |
| Superfamily | Hominoidea | Larger brains for body size; Specialized for semi-erect posture; Arm/shoulder structure identical; No bony external tail | Apes (gibbons, orangutans,gorillas, chimpanzees, bonobos), Humans |
| Family | Hominidae | Larger bodies, larger brains for body size | Great apes (orangutans, gorillas, chimpanzees, bonobos) and humans |
| Subfamily | Hominine | Larger brains for body size; near identical DNA | Chimpanzees, bonobos, and humans |
| Tribe | Hominini (hominins) | Specialized traits for bipedal locomotion | Humans (fossil and modern genera); this would include fossil members of the Genus Ardipithecus, Australopithecus, and Homo. |
| Genus | Homo | Larger brains for body size; near modern dentition | Modern humans, many fossil Hominins |
| Species | Homo sapiens | Modern skull morphology and size | Modern humans; first appeared ca. 200,000 ya |
As you move from the Kingdom level down to species, the listing of members on the right moves from a listing of distant to closer relatives. In other words, humans are related to cockroaches, since we are in the same Kingdom. We share some very basic animal traits with cockroaches, and yes, some of our DNA is identical. However, we are more closely related to birds and fish, which are in our same subphylum. We share more traits, and more DNA, with fellow Vertebrates. Since pigs, cats and dogs are fellow Mammals, we are more closely related to them than we are to birds. Of all mammals, we share the most traits, and the most DNA, with fellow Primates. Of all Primates, we share far more traits with apes (classified in our Superfamily) than we do with monkeys (who are only in our Suborder).
The only place we can get DNA is from our ancestors. The classification system is hence a listing of our close and distant relatives. We all share DNA, but we share more DNA with our closest relatives (in our case, the apes) because we have common ancestors closer to us in time than those we also share with the cockroach. (Thank goodness!) The classification system reflects our evolution and our relationship with all living things.