22 May 2016
Some time ago in Humanity as One I considered the unity of the human species, and, perhaps as significantly, how we discovered that unity. Beyond the woolly thinking and feel-good platitudes that tend to swamp any discussion of human unity, we know now from the genetic evidence contained within each and every human being that humanity constitutes a single species. But while it has become a stubborn problem in the philosophy of biology of how exactly to define species, the real message of the Darwinian conception of species is that of species anti-realism (for lack of a better term). Nature is continuous, and dividing up the natural world into biological taxa — species, genus, family, order, class, phylum, kingdom — is a convenience of human knowledge but ought not to be conceived as a Platonic form in biology, i.e., a template imposed upon nature, and not nature itself. So it is with the human species: we are a convenience of taxonomy, not a natural kind.
Given species anti-realism, it should surprise no one that all species are not alike; it may be a mistake to seek a single definition for what constitutes a species, though it is a habit of the Platonic frame of mind to settle on an essentialist definition. In biology specifically, for example, there is a long-standing tension between taxonomies based on some structural criterion or criteria (as in the Linnaean system) and taxonomies based on descent (evolutionary biology since Darwin). Marc Ereshefsky in his book The Poverty of the Linnaean Hierarchy advocates completely abandoning the Linnaean taxonomy and offers as an alternative “species pluralism,” asking whether, “Given the theoretical and pragmatic problems facing the Linnaean system, should biologists continue using that system?” With our contemporary naturalistic conception of human beings as one biological species among others, any change in our conception of species becomes a change in our conception of ourselves as a biological species. Might we define the human species in several different but equally valid ways?
In saying that humanity constitutes a single species we could express this comparatively in relation to other species. Because all species are not alike, a given species might, for example, represent more or less genetic diversity. (If we defined species by their genetic diversity, we would have a rather different taxonomy than that which we currently employ.) Geneticists discuss diversity in terms of nucleotide distance and heterozygosity; I will consider the latter as a measure for human genetic diversity. For example, human genetic diversity is lower than C. brenneri, a “bacteria-eating, 1-millimeter-long worm” (cf. The most genetically diverse animal; C. brenneri has been called “hyperdiverse” with a heterozygosity of around 40%, cf. Molecular hyperdiversity defines populations of the nematode Caenorhabditis brenneri), and higher than the San Nicolas population of island foxes off the coast of California (cf. Foxes on one of California’s Channel Islands have least genetic variation of all wild animals and Genomic Flatlining in the Endangered Island Fox). As I have sometimes cited the cheetah as a mammal population with very low genetic diversity (cf. Multiregional Cognitive Modernity), it is interesting to read that, the San Nicolas island fox, “has nearly an order of magnitude less genetic variation than any other low-diversity species, including the severely endangered African cheetah, Mountain gorilla, and Tasmanian devil.” (cf. Foxes on one of California’s Channel Islands have least genetic variation of all wild animals).
Now, I will admit that the first comparison with a little-known worm is not very enlightening, as we human beings, being part of the explosive adaptive radiation of mammals after the extinction of the dinosaurs, better understand comparisons with other mammals (cf. A Sentience-Rich Biosphere), and so a better comparison would be the mammal with the greatest genetic diversity. For a non-specialist like myself it is difficult to extract the relevant numbers from the context of scientific papers, but there seem to be mammal populations with significantly higher genetic diversity than human beings, just as there are mammal populations with significantly lower genetic diversity than human beings (on human genetic diversity generally cf. Human heterozygosity: A new estimate). The striped-mouse, Rhabdomys pumilio, has a heterozygosity (in some populations) of 7.3 %, significantly higher than the mammalian mean (there is an established mean heterozygosity for mammals of about 3.6 %, or H = 0.036; cf. Genetic variation in Rhabdomys pumilio (Sparrman 1784) — an allozyme study). The house mouse Mus musculus has populations with a genetic diversity of 8.9 % (H = 0.089). The extremely endangered Rhinoceros unicornis has a heterozygosity of nearly 10%, which may be the highest of any vertebrate (cf. Molecular Markers, Natural History and Evolution by J. C. Avise, p. 366).
It would be an oversimplification to rely exclusively on heterozygosity as a measure of genetic diversity, but at least it is a measure, and having a quantifiable measure gives us a different way to think about the human species, and a way to think about our species in relation to other species. The intellectual superstructure of agrarian-ecclesiastical civilization, which our industrial-technological civilization has inherited but not yet overcome, gave us the scala naturae, also known as the great chain of being (cf. my post Parsimony and Emergent Complexity). This conception also placed human beings in a context, and near the middle: higher than the animals, but lower than the angels. Genetic diversity places human beings in a naturalistic context that can (or, at least, could, with the proper motivation) be studied scientifically.
Are human beings being studied scientifically today? Yes and no. If you search Google for “highest genetic diversity” and “lowest genetic diversity” the top search results are all related to the perennially troubling question of human races (which I discussed in Against Natural History, Right and Left). On this point contemporary thought is so compromised that objective scientific research is impossible. This is unfortunate. More than 150 years after Darwin, the biology of human beings is still controversial. This ought to make any rational person wince.
What Freud once said of religion — “Where questions of religion are concerned, people are guilty of every possible sort of dishonesty and intellectual misdemeanour” — now appears to be true of humanity, which suggests that, despite Comte’s failed attempt to explicitly formulate a religion of humanity, an implicit religion of humanity has grown up almost unnoticed around the idea. This quasi-religious conception of humanity — which Francis Fukuyama expressed by saying, “we have drawn a red line around the human being and said that it is sacrosanct” (cf. Human Exceptionalism) — militates against any scientific self-understanding by humanity. This suggests an interesting possibility for defining a scientific civilization: a scientific civilization is a civilization in which the intelligent agent responsible for the civilization reflexively applies scientific understanding to itself. Scientific medicine studies human beings scientifically in order to keep them healthy and alive, but, with a few exceptions, human beings are not yet understood in a fully scientific context.
The scientific revolution set the stage for the possibility of a scientific civilization and for studying human beings in a fully scientific context. Neither of these possibilities have yet come to full fruition, and science itself has continued to develop and evolve, so that any scientific civilization or any conception of humanity based on contemporaneous science would have continually developed in parallel with the development of science. It is interesting to note that the scientific revolution begins about the same time as the Columbian Exchange, which latter essentially unified the human species again after our global diaspora (this was the theme of my earlier Humanity as One), in which populations had become separated and did not know themselves to be one species. The sense of humanity as one that emerges from the global unification of the Columbian Exchange and the sense of humanity as one that emerges from science both give us a planetary conception of humanity that might well be called the overview effect as applied specifically to humanity. I would call this “The Human Overview,” except that I have already used this to indicate the comprehensive impression we derive from meeting with and speaking to another.
I would argue now that we are capable of transcending even this planetary conception of humanity because of the recent extrapolation of biology as astrobiology. Science from the scientific revolution to the middle of the twentieth century was the science of a species exclusively subject to planetary endemism, and even though we overcame geocentrism in a narrow sense, our conceptions of the world and of ourselves often remained subject to geocentrism in an extended sense; the intellectual equivalent of geocentrism is the projection of the assumptions of planetary endemism onto our categories of thought. With the first glimpse of the Earth from space (i.e., the overview effect) and a growing awareness of the cosmological context of our planetary system, we began to transcend this intellectual equivalent of geocentrism. One of the consequences of this has been astrobiology, which places biology in a cosmological context, and, in so far as we understand humanity scientifically, places humanity also in a cosmological context.
Astrobiology would be impossible without both contemporary cosmology and biology; cosmology gives the scope of the conception, and biology the depth. With our increasing knowledge of cosmology and growing sophistication in biology, we have the intellectual resources now to formulate the human condition in a cosmological context and hence to understand ourselves scientifically — if only we have the strength of mind to do so. While such a conception of humanity would be “mere humanity” without the overlay of theological, soteriological, eschatological and teleological concepts that have been used in the past to develop a more comprehensive conception of humanity — what I elsewhere called, “the hopeless tangle of rationalization and cognitive bias that we have painstakingly erected around the idea of humanity” — this “mere humanity” is far more noble and edifying in its simplicity than past attempts to guild the lily.
As a species we have a long and painful history of perverting the ideals we have chosen for ourselves and making the human condition much worse than it was before any such ideals were conceived. As Montaigne noted, men, in seeking to become angels, transformed themselves into beasts (cf. Transcendental Humors). Among these brutal ideals I would count all the theological, soteriological, eschatological and teleological concepts that have been used to flesh out the concept of humanity, while the “darkling aspiration” (“dunklen Drange”) of a Faust has proved not to be our undoing, but rather to be what is best in humanity. In the past, our aspiration to embody perverted ideals in our own lives resulted in raising up as false idols fragmented and partial conceptions of humanity; individuals sought to become some particular kind of humanity (rather than “Mere Humanity”), and accounted this striving as a form of virtue, when it is, in fact, the spirit of ethnic cleansing. The planetary conception of humanity, and indeed the astrobiological conception of humanity, gives the lie to all of this. Soon it will be vain to aspire to be anything other than merely human, and soon after that it will be vain to aspire to be human (i.e., exclusively human). But the way to this understanding is through science and a rigorously scientific conception of humanity.
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