Systematics and Evolution 131underlined or italicized). For example, we belong to the genus Homo (Latin for “human”)
and the trivial name of our species is sapiens (Latin for “thinking”), so our full species name
is Homo sapiens or H. sapiens. The trivial name can never stand by itself, but must always be
paired with the genus because trivial names are used over and over, but a generic name can
never be used for another animal. The genus (plural, genera) can be composed of a single
species or more than one species. Our genus Homo includes not only H. sapiens, but also
H. erectus, H. neanderthalensis, H. habilis, H. rudolfensis, and several other extinct species, such
as the newly discovered H. naledi. Genera are clustered into larger groups called families,
which always end with the suffix “-idae” in the animals and “-aceae” in plants. Our family is
the Hominidae, while the Old World monkeys are the Cercopithecidae, and the New World
monkeys are the Cebidae. Families are clustered into orders (which have no standardized
ending or format), such as the order Primates (which includes all monkeys, apes, lemurs,
and humans), the order Carnivora (cats, dogs, bears, and their flesh-eating relatives), or the
order Rodentia (the rodents, the largest order of mammals on earth). Orders are then clus-
tered into classes such as the class Mammalia, or mammals, including all the orders just
listed. The class Mammalia is clustered along with the classes for birds, reptiles, amphibians,
and fish into the phylum Chordata (all animals with a backbone or its precursors). Finally,
there are a number of phyla (mollusks, arthropods, worms, echinoderms, etc.) that cluster
with the chordates in the kingdom Animalia.
Although this system is over 360 years old, it has powerful advantages. The Linnaean
classification scheme is flexible, allowing groups and new taxa to be changed, shuffled, and
inserted as the situation demands. Taxonomic names were traditionally based on Greek or
Latin roots, or Latinized forms of other words, because Latin was the language of scholars in
Linnaeus’s time. Although most scholars around the world no longer read Latin, the fact that
the names are accepted worldwide means that no matter what language a biologist speaks,
the names of the animals are consistent. You can pick up a journal article in an entirely
different orthography, like Russian Cyrillic or Mandarin Chinese, and still recognize the
Linnaean names. By contrast, every language has its own local names for familiar animals.
Even within the United States, “gopher” could mean a small burrowing rodent in some
regions, or a tortoise in others—but the scientific names for the rodent genus Geomys and the
tortoise genus Gopherus are universally recognized and unambiguous.
When Linnaeus set up his “natural system,” his goal was to understand the mind of
God by understanding how his handiwork was arranged. Ironically, the system he devel-
oped was hierarchical, showing that life has a branching structure like a tree or bush. That
branching structure of life became one of Darwin’s best arguments for the fact of evolution
(discussed in chapter 4). Taxonomy shifted its goals from theology to understanding life’s
evolutionary history. Consequently, the practice of systematics has had to make some impor-
tant decisions about what criteria are used in classification. Should taxonomy be based solely
on evolutionary history or should other components (such as ecology) also be included?
Ecologically speaking, many people lump all swimming vertebrates with fins together as
“fish.” But not all fish are the same. Lungfish are actually more closely related to amphib-
ians, reptiles, and us than they are to a tuna fish. In taxonomic terms, lungfish do not belong
with fish but with the four-legged land animals in a group known as the Sarcopterygii
(the lobe-finned fish and their descendants). Even though that is an accurate picture of evo-
lutionary relationships, many biologists have trouble with thinking about organisms this
way and prefer groups that reflect some ecology as well.