Monday, November 22, 2021

You Are Here: Human Taxonomy

Click to see Vol. I, Issue 4 of the newsletter in which this article first appeared.

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As I'm sure you're aware, you and I and every person we know is referred to scientifically as Homo sapiens, which can be translated as "the hominid who knows." (We'll get to "hominid" in a minute.) Others have translated it "knowledgeable man" or even "wise man." (But it seems to me that saying "man" here begs the question.)

These two words, Homo and sapiens, are the genus and species of humans. There are (or actually were) other species in our genus, but we are, as it were, the last men standing.

Carl Linnaeus, the Swedish scientist who came up with the original naming system on which the one we use today is based, declared that all living beings would be referred to by both genus and species (this is called binomial nomenclature, or "two-named naming), though taken together they are called "the species name." So the species name of

  • one kind of hummingbird is Topaza pella (topaz is a gemstone; pellus is Latin for "dark-colored");
  • a certain water buffalo, Bubalus bubalis (from Greek boubalos meaning "buffalo");
  • a type of orchid, Ophrys apifera (the "bee orchid"); and
  • the giant sequoia tree, Sequoiadendron giganteum (the "giant tree of Sequoia," also called the giant redwood, among other names).
Hummingbird, Water Buffalo, Orchid, Sequoia

(Not to confuse you, but sometimes another, third, word is added to describe a subspecies, but never mind.)

Notice also that the genus name is always capitalized, and the species (or subspecies) is not. In fact, the names of any members of ranks above genus are always capitalized. For example, the water buffalo is in the family Bovidae (which includes cows, sheep, antelopes, and the like). (All names of ranks, including the species, are customarily italicized.)

Okay, but how are we related to hummingbirds, buffaloes, orchids, and sequoias, let alone bacteria and whatnot? In a moment we'll begin our slow climb up the family tree, from the most specific grouping - us - to the largest, but first let's get a little background.

Taxonomic Ranks

For the moment, let's start at the top and climb down to us. The largest divisions of living things are the domains, of which there are only three. (There is in fact a category outside of any domain--the viruses--though some dispute that they are "living" in any full sense of the word. We'll get to that.)

By the way, taxonomy is the science of categorization or classification. The units of classification are called taxa (singular taxon); -nomy, or course, means the "laws" or "science" of something. The word can be used generally for classifying things like library books, but here we're talking about a "hierarchical classification of living things."

Next are the kingdoms, of which there are five (usually), though most of us only think of the animal and plant kingdoms.

Continuing downward, in zoology we have the phyla (singular phylum), which in botany are called divisions. In the five-kingdom system, there are something like 31 phyla of Animals and 14 divisions of plants. For completeness's sake, let me add that there are 8 of Fungi, 19 of Protista, and 29 of Bacteria. Again, more details later.

Below phylum on our Ladder of Life is class. Things start to get messy here; as we get up to larger and larger groups, there are more of what we might call "inter-ranks." For example, around "class" we have superclass above; then subclass, infraclass, subterclass, and parvclass below. We will not spend a lot of time on these details!

Let's speed on down the ranks. The lowest four categories are orders (which may have superorders and/or suborders), families (with superfamilies, subfamilies, tribes, and subtribes), and the genus and species we've already met, the latter of which (as mentioned) may have a subspecies.

Let me note here that nothing in the science of taxonomy is fixed. New knowledge brings new classifications, and taxonomists may even disagree on what belongs where at any given moment. The introduction of DNA, a more certain indicator than physical descriptions, has revolutionized this science.

If you're planning to memorize the eight ranks, here's one of the many mnemonics used by students:

"Dear King Philip Came Over For Good Soup."

Look at the initial letters: they'll remind you of:

Domain, Kingdom, Phylum, Class, Order, Family, Genus, and Species.

Right? By the way, botanists can use "Dear King David" (remember they have Divisions) for "Dear King Philip."

Now that you've learned the eight ranks (can you name them?), let's move on to us.

Human Taxonomy

We will now climb up our family tree, from the specific to the general.

Genus and Species: We have already discussed our full species name (genus + species), but let's take a closer look at the genus name Homo.

Homo is the Latin word for man, as seen in the Latin translation of Pontius Pilate's words "Behold the man": Ecce homo (which has become a motif in religious art). It should not be confused with the Greek root homo-. meaning "same," as in homogeneous and homosexual. Latin Homo is the source word for human, and in turn may have come from humus meaning "earth" or "soil."

We are the only extant example of the genus Homo; all others have gone extinct. The first emerged from the genus Australopithecus, let's say a couple of million years ago. The earliest known Homo was Homo habilis ("handy man"--heh heh). Others include Homo erectus ("upright man," who stood erect) and the famed Neanderthal Man, Homo neanderthalensis. All of these seem to have lived in groups whose lifestyles we might recognize; by the time of H. erectus we were probably living in societies of hunter-gatherers and using fire. (Everything this far back must be stated as "probable"; science itself evolves!)

Australopithecus went extinct not too long after Homo emerged. H. erectus may have gone "extinct" around a half a million years ago, probably by diverging into new species. H. habilis stuck around until around 1.65 million years ago, and H. neanderthalensis seems to have lived for quite some time side-by-side with us: they were here until around 40,000 years ago, and may have gone extinct through climate change, disease, or--very possibly--interbreeding with us.

The "chain" of our development looks like: Australopithecus --> H. erectus --> us. H. habilis and Neanderthal Man were on lateral branches.

We, the "anatomically modern humans," emerged roughly a quarter of a million years ago, probably in Africa. We then migrated into areas of Asia and Europe already occupied by Neanderthals.

A dictionary article describes us as "bipedal primates" characterized by

a large brain, a nearly vertical forehead, a skeletal build lighter and teeth smaller than earlier humans, and dependence upon language and the creation and utilization of complex tools.

(We'll talk more about primates in a minute.)


Family: Hominidae. These are the "great apes," sometimes called in English "hominids." Aside from our genus, Homo, there are three other genera (the plural of genus): the Pongos include three types of orangutan; there are two types of Gorillas; and two types of Pans (chimpanzees and bonobos).

Our family includes two sub-groups or "inter-ranks" into which we fall:

  • the subfamily Homininae and
  • the tribe Hominini.

Aside from our tribe, the subfamily Homininae includes the tribe Gorillini, the two species of gorillas (all tribes end in -ini).

And our tribe the Hominini has another genus besides us, the Pans (chimpanzees and bonobos). I hope this chart helps:

Don't trouble yourself too much about these details. I have included them here just to emphasize our close relatives. But in our long climb up the family tree, it's enough to know that we are of the Genus Homo and the family Hominidae.


Order: Primates. Now here's a word you may have heard before. Along with the other Hominidae (the "great apes"), we belong with the gibbons, monkeys (New World and Old), tarsiers, lemurs, and lorises to the order of Primates. As the groups get larger (and our relationships get more remote), I'll give up trying to cover all the members. It's enough to say that we are in the suborder Haplorhini, along with all that I've named except the lemurs and lorises; and in the infraorder Simiiformes, which we call "simians": the "great apes" (the Hominidae plus gibbons), the monkeys, and us. No tarsiers, lemurs, or lorises; the simians are more humanoid.


Class: Mammalia. Commonly known as "mammals," these are characterized by mammary glands for nursing the young with milk (mamma is the Latin word for "breast"), and are covered with hair or fur. We typically (but not always) have four limbs (the sea-going cetaceans, like dolphins and whales, have only two, modified into fins), and also typically (but not always) bear our young alive (the five species of monotremes, including the platypus, are egg-laying mammals).

Orders include rodents; bats; the Eulipotyphla (ground-dwellers like moles and shrews); Artiodactyla (including cetaceans and some hoofed animals); Carnivora (meat-eaters like big cats, wolves, and our mammalian companions, cats and dogs); and us Primates.


Phylum: Chordata. This essentially means "critters that at some point in their development have a notochord," a structure along the back similar to a spine. If, as we do, that chordate has developed a backbone made up of vertebrae, it's called, as we are, a vertebrate. The vertebrates are a subphylum that includes about 69,963 species, from frogs to the blue whale, including all fish, amphibians, reptiles, birds, and mammals (that's us). There are other, invertebrate, chordates, mainly marine animals like sea squirts.

A sea squirt


Kingdom: Animalia. Now here's a word we use all the time: animals. For most of us, that means "living things that aren't plants," but it's a little more complicated than that.

That, however, was the way the ancients saw things--before microscopes, anyway. With the introduction of new equipment, though, scientists could see little things that seemed to be neither plant nor animal (or maybe both/and). They called these protista, a third kingdom.

Then, once they recognized that some microscopic critters had cell nuclei and some didn't, they named those with "eukaryotes" (that includes us) and those without "prokaryotes." The prokaryotes are now called Monera, and include bacteria. Today the Monera rest in their own domain called Prokaryota; the rest of us, including the Protista, Plantae, and Animalia are in the domain Eukaryota.

Finally, the Fungi were recognized as fundamentally different from plants (they do not carry out photosynthesis, for example) and so we now have a "five-kingdom system."

There have been suggestions of systems of six, seven, or even eight kingdoms, but five is the standard. These are, again:

  • Animalia
  • Plantae
  • Fungi
  • Protista (microscopic with cell nuclei)
  • Monera (microscopic without cell nuclei)

As for the Animalia, we can be recognized by the following traits: we usually consume organic material ("food"); breathe oxygen ("air"); are able to move intentionally; and can reproduce sexually. For the most part, we know an animal when we see one.


Domain: Eukaryotes. The first four of the kingdoms just listed belong to the domain of Eukaryota (creatures with cell nuclei); the last is in the domain Prokaryota (those lacking nuclei). We, of course, are Eukaryotes.

But here's a peculiar thing, that makes simple family trees difficult to draw: there are three domains. The Eukaryotes are all in one; that's easy. But the Prokaryotes are actually split into two domains: molecular analysis has shown that the RNA markers in Bacteria are significantly different from the Archaea (such as the methanogens, which produce methane gas), the third domain.

This leads the discussion in a whole new direction, one which may not be very useful for us. But while we're off-roading, let's add that no one knows quite where to place viruses. They cannot replicate outside of living hosts, so there is some speculation that they may not be "living things" at all. Are they a form of life? Or merely an organic molecule? It's hard to say, but it does point out that taxonomy, like all science, can be slippery.


Above all the ranks we've examined is the realm of life, or "all living things." We can say that rocks are not alive, and butterflies are. But the viruses make that distinction harder to prove.

Sticking with what we know, and using only the eight main ranks, we can say that we humans are members of the following, from the top down again:

  • Domain: Eukaryotes (which have cell nuclei)
  • Kingdom: Animalia (which eat food, breathe oxygen, move independently, and reproduce sexually)
  • Phylum: Chordata (which have a notochord at some point in development)
  • Class: Mammalia (which feed babies from mammary glands, have hair or fur, and usually bear live young)
  • Order: Primates (the great apes plus gibbons, monkeys, tarsiers, lemurs, and lorises)
  • Family: Hominidae (the great apes only--orangutans, gorillas, chimpanzees and bonobos, and us)
  • Genus: Homo (only us now, but many closely-related extinct ancestors and relatives)
  • Species: Homo sapiens

If I were to add one "inter-rank," I'd say it's most important to point out that we are of the Subphylum Vertebrata--creatures with backbones.


And that just about wraps things up. You should now be able to point to our particular twig on the "Great Tree of Life," and say: "I am here!"

Click here to see a HUGE version of Haeckel's Tree


Matching: Match the term for humans to its rank. Correct answers are in the first comment below.

  1. Domain
  2. Kingdom
  3. Phylum
  4. Class
  5. Order
  6. Family
  7. Genus
  8. Species

  1. Primates
  2. Animalia
  3. Homo
  4. Chordata
  5. Homo sapiens
  6. Mammalia
  7. Eukaryotes
  8. Hominidae


Choose the best answer. Correct answers are in the first comment below.

  1. A giraffe is a member of the Class:
    A. Mammals
    B. Plantae
    C. Prokaryotes
    D. Primates

  2. A duck is a member of the Kingdom:
    A. Plantae
    B. Mammalia
    C. Animalia
    D. Invertebrates

  3. Which rank is the highest (above the others)? Use the mnemonic!
    A. Class
    B. Family
    C. Phylum
    D. Order

  4. How many species of the genus Homo are alive today?
    A. one
    B. seven
    C. 69,963
    D. unknown

  5. Humans and orangutans belong to the same:
    A. family
    B. subfamily
    C. tribe
    D. genus

Questions to Think About: These questions do not have "right" or "wrong" answers. They only ask your opinion.

  1. Why do you think DNA is a more reliable guide to taxonomy than the observations of differences in organisms?
  2. Why do you think other species in the genus Homo have all gone extinct? Could the same thing happen to us?
  3. What practical value could there be in classifying every living organism on earth?

1 comment:


    Practice: 1. G; 2. B; 3. D; 4. F; 5. A; 6. H; 7. C; 8. E

    Questions to Answer: 1. A; 2. C; 3. C; 4. A; 5. A

    Questions to Think About do not have any single correct answer. However, any answers you give should be supported by what you read or by things you know ("I think... because...").