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The Hierarchical Nature of Living Systems, Species, and Race

2100 words

Biology is one of the most interesting sciences since, at its core, it is the study of life and living systems. The biological organization of living systems and the ecosystems these living systems find themselves in are interesting to learn about, since we can then discern different species and learn how and when to delineate separate species based on a set of pre-conceived measures. The classification of human races in these systems will be discussed, along with why human races are not different species.

The organization of living systems

Living systems show hierarchical organization, each system—from the physiological to the physical—interacting with each other. However, a key factor in the organization of these interactions is the degree of the complexity of the interactions in question. We can look at the organization of the biological world as hierarchical—that is, each level builds on the preceding level, so we get from atoms to the biosphere and everything in between is what we call “life” and also show how these complex, living biological systems live and exist due to the hierarchical organization of living systems. The point is, life does not have a simple definition, but all living systems share similar characteristics that can describe life. Biologists organize living systems hierarchically, from the subcellular level to the entire biosphere, and then study the interactions that occur which cannot be predicted from just studying the sum of its parts. This is why a holistic—and not reductionistic—approach needs to be taken when studying and describing living systems.

The hierarchy is:

The cellular level, which includes: atoms, molecules, macromolecules, and organelles; the organismal level which include: tissue, organs, the organ system, and the organism; the populational level which includes: the population, species, and the community; and finally the highest level, the ecosystem level which includes the ecosystem and the biosphere.

At the cellular level, we have atoms which are the fundamental elements of matter and are joined together by chemical bonds called molecules. large and complex molecules are called macromolecules, DNA—which stores hereditary information—is a type of macromolecule. Complex biological molecules are then assembled into organelles, where cellular activities are organized. A mitochondrion is, for example, an organelle with a cell that extracted energy from consumed food molecules. And finally, we have cells, which are the basic unit of life.

Next, we have the organismal level, and cells of multicellular organisms make up three levels of organization. Tissues, which are groups of similar cells which function together as a unit. Tissues then are grouped into organs which are structures of the body which are composed of many different kinds of tissues which act in a structural manner and as a unit. Then we have organ systems, such as the nervous system which is the sensory organs, brain and spinal cord, and the network of neurons that convey signals to different parts of the body.

Then we have the populational level. This includes the individual organisms which occupy various hierarchical levels in the biological world. A population is a group of organisms all living in the same place. Together, all populations of a particular kind form a species—members of a species must look similar and be able to interbreed. Then finally, we have the biological community which consists of all of the populations coexisting together in one place.

Lastly, we have the ecosystem level. This is the highest tier of biological organization (the lowest being the cellular level). A biological community and its physical habitat (such as soil composition, available water etc) in which it finds itself in and lives and competes with other organisms constitute an ecosystem while the entire planet is the highest of all levels of biological organization—the biosphere. All of these systems together can be seen as the hierarchical organization of living systems.

(See Mason et al, 2018 for more discussion of the above points.)

Organismal classification

Now, in these differing biological hierarchies, we find differing Eukarya, Prokarya, and Bacteria. The in-use classification system is the Linnean hierarchy. Differences exist between organisms, this is obvious. But it is a bit more tricky to classify these organisms and place them into like groups. Then, in the 1750s, Carolus Linnaeus came along and instituted a binomial classification system for organisms—the most commonly-known binomial being Homo sapiens—which was much simpler than the polynomial names

The hierarchy is as follows:

1. Species;

2. Genus;

3. Family;

4. Order;

5. Class;

6. Phylum;

7. Kingdom; and

8. Domain. Domains can then be split into Archaea, Bacteria, and Eukarya. Domains are the largest taxons, being that they comprise every organism that we know of.

For example, our species is sapiens, our genus is Homo, our family is Hominidae, our order is primates, our class is Mammalia, our phylum is Chordata (with a subphylum Craniata), our kingdom is Animalia and our domain is Eukarya. This is our species’ taxonomic classification.

The traditional classification system—the Linnean system—groups species into genera, families, orders, classes, phyla, and kingdoms. Thus, these systems classify different organisms on the basis of similar traits, and since they consist of a mix of derived and ancestral traits, they do not necessarily take into account different evolutionary relationships.

There are of course limitations to the Linnean hierarchy:

1) Many “higher” taxonomic ranks are not monophyletic and so do not represent real groups (like Reptilia). For something to be a “natural group”, a common ancestor and its descendants must all derive from descent from a common ancestor, so any other type of taxonomic ranks are created by taxonomists, such as paraphyletic and polyphyletic.

2) Linnean ranks are not equivalent. Two families may not represent clades that arose at the same time, because one family may have diverged millions of years before the other family and so the two families had differing amounts of time to diverge and acquire new traits. So comparisons in the Linnean sense may be misleading and we should then use hypotheses of phylogenetic relationships.

What is a species?

It should first be noted that species are, indeed, real. New species arise when isolated organisms of one population become genetically/geographically isolated for a period of time. Over time, as the split population spends time geographically and genetically isolated, they cannot interbreed with the parent population and thusly attain separate species status. This is the received view, the biological species concept.

There are a wide range of species concepts and they all capture the differences that different theorists believe we should emphasize in our classification of organisms.

The phenetic species which appeal to the intrinsic similarities of organisms. The biological species concept which appeals to reproductive isolation (one version of the biological species concept is the recognition concept, which defines species as a system of mating recognition. The cohesion species concept which generalizes the biological species concept and it recognizes that gene flow isn’t the only factor that holds a population together and makes it different from other populations. The ecological species concept which defines species by appealing to the fact that members of a species are in competition with one another because of the need the same resources. And the phylogenetic and evolutionary species concept which define species as segments on the tree of life (the phylogenetic species concept, for instance, holds the term ‘species’ should be reserved for groups of populations that have been evolving independently of other populations.

Sterelny and Griffiths (1999) tackled this in their book Sex and Death: An Introduction to Philosophy of Biology:

While we think cladism presents the best view of systematics, biological classification nevertheless poses an unsolved problem. If we were to accept either evolutionary taxonomy, which builds disparity into its classification system, or phenetic taxonomy, which is based on the idea of nested levels of similarity, traditonal taxonomic levels would be quite defensible. Within those taxonomic pictures, the idea of genus, family, order, and so on makes quite good sense. If cladism is the only defensible picture of systematics, the situation is more troubling. From that perspective, these taxonomic ranks make little sense. Cladists do not think there is a well-defined objective notion of the amount of evolutionary divergence. That, in part, is why they are cladists. Hence, they do not think there will be any robust answer to the questions, when should we call a monophyletic group of species a genus? a family? an order? Only monophyletic groups should be called anything, for they are well-defined chucnks of the tree. But only science greets the question, are the chimps plus humans a genus? It has long been receieved wisdom in taxonomy that there is something arbitrary about taxonomic classification above species. These decisions are judgement calls. So cladists only show a somewhat more extreme version of a skepticism that has long existed. The problem of high taxonomic ranks would not matter except for the importance of the information expressed using them. Hence cladism reinforces the worry that when, for example, we consider divergent extinction and survival patterns, our data may not be tobust, for our units may not be commensurable. Unfortunately, it does this without suggesting much of a cure.

Where does race fit in?

Racehood is simple: A race is a group of humans that: Condition 1; is distinguished from other groups of humans by patterns of visible physical features; Condition 2: is linked by common geographic ancestry which is peculiar to members of this group; and Condition 3: originates from a distinctive geographic location.

So now all we need to do is go through four steps: 1) recognize that there are patterns of visible physical features which correspond to geographic ancestry; 2) observe that these patterns of visible physical features which correspond to geographic ancestry are exhibited between real, existing groups; 3) note that these real existing groups that exhibit these patterns by geographic ancestry satisfy C1-C3; and 4) infer that race exists.

Some may argue that the races are different species, citing the same patterns of visible physical features discussed above. However, if we are referring to the biological species concept, then the human races are not different species at all since all human races can produce fertile offspring with one another. Our genus, of course, is Homo, all of the human races are the same genus; though some may attempt to use the previously-discussed conditions for racehood as conditions for specieshood for humans, the most preferred method for delineating species currently is the biological species concept, and since all of the human races can produce fertile offspring then the human races are not different species.

In keeping with the classification system that is currently used today (see above), where would human races fit into our taxonomy? Falling within our species sapiens seems like a good start, and since the races can interbreed and have fertile offspring, then they are not different species but are the same species, despite phenotypic differences. Thus, human races would be within species but under subspecies. Using this line of logic, human races cannot be different species, despite claims to the contrary that human races are different species based on patterns of visible physical features which correspond to geographic ancestry. That’s enough to denote racehood, not specieshood.


The study of life—in all of its forms and in all of its environments—is one of the most important things we, as humans, can do. From it, we can learn where we came from and even—possibly—where we may be going. Once we understood the biological hierarchy and how upper levels are built from lower levels working together, then we were better able to understand how living systems act on the inside—cellularly and physiologically—to the outside—organismal and environmental interaction. From organismal and environmental interaction, speciation may occur. The highest level of the organization of living systems is the biosphere—and it is so because the living systems that are driven by the smallest cellular interactions interact with other species, the ecosystem and the biosphere.

Species do exist, but there are numerous species concepts—over twenty. One of the more popular species concepts in use is the cladistic species concept. In this species concept, a species is a lineage of populations between two specific branch points. The cladistic concept thusly recognizes differing species by differing branch points and how much change occurs between them (see Ridley, 1989).

The classification of different organisms into different species is pretty straightforward, though it falls prey to oversimplification since it only focuses on similar traits. Species exist, this is established. But races are not species, contrary to some beliefs. Different races can interbreed and, I would argue, that for there to be separate species, human races would not be able to interbreed. Yes, there are physical and morphological differences between races, but, as argued, this is not enough to denote speciation, but it is enough to denote raciation.