This Island Earth

Some time ago (on Twitter) I observed that astrobiology is island biogeography writ large. I return to this idea regularly, but have not yet adequately fleshed it out. I touched on this again in From an Astrobiological Point of View, but it would take considerable exposition to do justice to the idea. This post is an unsatisfactory response to my return to an idea that deserves to be studied in his own right and at some length.

Chart of the Galápagos Islands

Chart of the Galápagos Islands

Island biogeography has its origins in the origins of Darwin’s Origin of Species. As we all know, Darwin visited the Galápagos Islands during the voyage of the Beagle that Darwin recounted in The Voyage of the Beagle. Decades of thought and gestation followed, but it was in part the peculiar mix of species in the Galápagos that was crucial for Darwin’s breakthrough to the idea of natural selection. I have myself visited the Galápagos Islands (I wrote about this in Happy Birthday Charles Darwin!) and it is a spectacular lesson in natural history that I cannot recommend highly enough.

theory of island biogeography

Although island biogeography begins with Darwin, it was brought to explicit formulation and theoretical maturity by E. O. Wilson and Robert H. MacArthur in The Theory of Island Biogeography. There the authors say in their opening remarks:

“By studying clusters of islands, biologists view a simpler microcosm of the seemingly infinite complexity of continental and oceanic biogeography. Islands offer an additional advantage in being more numerous than continents and oceans. By their very multiplicity, and variation in shape, size, degree of isolation, and ecology, islands provide the necessary replications in natural ‘experiments’ by which evolutionary hypotheses can be tested.”

Robert H. MacArthur and Edward O. Wilson, The Theory of Island Biogeography, Princeton: Princeton University Press, 1967, Chap. 1, p. 3

Much of this remains valid when translated, mutatis mutandis, into astrobiology. The key, however, is how one goes about arriving at the mutatis mutandis. How can all other things remain equal when we are translating from terrestrial ecosystems in miniature, thus a bit easier to understand than the whole of the terrestrial biosphere, or some major division such as a biome, into worlds entire isolated in the blackness of interplanetary and interstellar space? The analogy is not perfect, but it is suggestive of parallel avenues of approach.

How do you quantify the life of an entire world? Higher biological taxa. This graph shows families rather than species.

How do you quantify the life of an entire world? Higher biological taxa. This graph shows families rather than species.

Scaling up biogeography

While the flora and fauna of islands are sufficiently restricted in scope to make it possible to do a detailed count not only of species present (already in The Voyage of the Beagle we see Darwin noting the number of genera and species present on various islands), but sometimes also of individuals. Obviously we are not going to be able to count species, much less individuals, for entire worlds. We must draw back, look at the big picture, and employ the kind of metrics we see in studies of mass extinctions. In detailing the loss of biodiversity of mass extinctions it is not merely species or even genera that go extinct; sometimes entire families, orders, and classes go extinct. These we can count; in fact, we could reasonably expect to count higher taxa for entire worlds.

taxnomic rank

The reformulation of island biogeographical ideas for astrobiology will be the labor of the production of a new science. The scaling up of our scope to higher biological taxa is only one among many scaling changes in our thought we must pursue in order to develop concepts adequate to the fate of life in the context of galactic ecology.

galactic ecology

Flight and its Technological Equivalents

Geologically young islands — as with the well-known example of the Galápagos Islands, mentioned above — are primarily populated by birds and marine animals. Birds bring with them a variety of plant life; moreover, many plants can float, and are brought to islands by ocean currents. Least common to arrive and to survive are those terrestrial species that find themselves on islands due to sweepstakes dispersal routes, i.e., somewhat unusual circumstances in which a breeding pair of terrestrial animals are able to ride a floating log or mass of vegetation to an otherwise isolated island and can there reproduce, like the marine iguanas on the Galápagos, who have learned to feed by diving into the ocean and forage on inter- and subtidal algae. That is to say, the least common colonists are life forms that cannot swim or fly; being able to traverse planetary distances is a limiting factor in the distribution of a life form.

Darwin Greenhouse

Darwin conducted a simple yet ingenious ecological experiment in island biogeography that he recounted in The Origin of Species:

“I have before mentioned that earth occasionally, though rarely, adheres in some quantity to the feet and beaks of birds. Wading birds, which frequent the muddy edges of ponds, if suddenly flushed, would be the most likely to have muddy feet. Birds of this order I can show are the greatest wanderers, and are occasionally found on the most remote and barren islands in the open ocean; they would not be likely to alight on the surface of the sea, so that the dirt would not be washed off their feet; when making land, they would be sure to fly to their natural fresh-water haunts. I do not believe that botanists are aware how charged the mud of ponds is with seeds: I have tried several little experiments, but will here give only the most striking case: I took in February three table-spoonfuls of mud from three different points, beneath water, on the edge of a little pond; this mud when dry weighed only 6¾ ounces; I kept it covered up in my study for six months, pulling up and counting each plant as it grew; the plants were of many kinds, and were altogether 537 in number; and yet the viscid mud was all contained in a breakfast cup! Considering these facts, I think it would be an inexplicable circumstance if water-birds did not transport the seeds of fresh-water plants to vast distances, and if consequently the range of these plants was not very great. The same agency may have come into play with the eggs of some of the smaller fresh-water animals.”

Charles Darwin, On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life, London: John Murray, 1st edition, 1859, GEOGRAPHICAL DISTRIBUTION. CHAP. XII., pp. 386-387

Such is the power of flight to widely disperse species over the surface of Earth. Flight has a value beyond the differential survival and reproduction advantage that it confers upon those species so endowed; it also plays a co-evolutionary role at the largest scale of planetary ecology. That flight should develop within a biosphere is perhaps not inevitable, but we could say instead that a biosphere in which flight emerges is likely to achieve much higher levels of biodiversity, and hence prove a more robust ecosystem. A robust ecosystem, in turn, is more likely to survive existential threats (such as the mass extinctions that have repeatedly punctuated the evolution of life on Earth), so that planetary biospheres of a given longevity are more likely to have flight than not.

convergent flight

Natural selection found several different solutions to the problem of flight. Some small plant seeds, and some very small animals (e.g., spiders), are light enough to be carried by the wind. Some animals fly by gliding (flying squirrels), and some animals employ wings for flight. Wings have emerged separately among insects, dinosaurs, birds, and mammals. Flying fish might also be said to have wings. Given a biosphere not disrupted by the anthropocene, flying fish might eventually transition to a fully flying way of life; this may yet happen in the distant future.



The problem of flight at the level that concerns astrobiology is potentially as diverse as the solutions to the problem of flight in a planetary biosphere. We are only just beginning to understand the complexity of the universe in which we live, and we are continually discovering capacities of nature and of life that previously would have strained our credulity. Just last week on the second episode of The Unseen Podcast, host Paul Carr noted that, with all the exchange of material between the inner planets of the solar system, we would not be surprised to find that all this life comes to the same root, while we probably would be surprised, if found like the oceans of the moons of Jupiter and Saturn, if it came from the same root. That far out in the solar system, we would expect a second genesis if there is any life at all.

If there is life in the subsurface ocean of Europa, we expect that life to be the result of a second genesis.

If there is life in the subsurface ocean of Europa, we expect that life to be the result of a second genesis.

That perspective on the likelihood the relations of life within the confines of a single solar system may change as we learn more about astrobiology. But so far this discussion is primarily a matter of naturally occurring dispersal vectors for species. We must consider astrobiology both before and after technologically-driven dispersal vectors, as well as in regard to terrestrial and to extraterrestrial dispersal vectors. Just as technological dispersal vectors have began to play a major role in our planetary biosphere, especially in relation to the distribution and introduction of invasive species, we would expect a mixture of both natural and technical dispersal vectors in astrobiology.


Spaceflight is to astrobiology as flight is to biogeography.

Given the continuity of natural history and civilization, that spaceflight is to astrobiology as flight is to biogeography follows naturally in the strict sense of “naturally.” In other words, there is a continuity from flight as the result of biology and flight as the result of technology; there is idea diffusion (or idea flow) from nature to civilization: we observe the existence proof of powered, heavier-than-air flight in nature, and we seek to reverse engineer this development and to reproduce it with technology. Thus, in a sense, technology is the pursuit of biology by other means. Thus spaceflight, as the technological equivalent of biological flight, will play a co-evolutionary role at the largest scale of galactic ecology.

flight 2

It may be worth noting in this context that the cluster of developments dependent upon human activity — intelligence, technology, language, and civilization among them — could be said to represent a solution to the problem of survival, but it is a “solution” that we find no where else in nature except in ourselves. Now, in referring to “nature” in the previous sentence I here mean “in the terrestrial biosphere.” This is significant, because a viable solution to the problem of survival (as we can see from the example of flight, or I might also use the example of vision) tends to be repeatedly emergent in nature, so that we find multiple instances of homology and convergent evolution. We do not find this in regard to the human solution to the problem of survival.

If this is a solution to the problem of survival as posed by the terrestrial environment, why did no other species exploit this strategy?

If this is a solution to the problem of survival as posed by the terrestrial environment, why did no other species exploit this strategy?

On a larger scale, a scale at which “nature” does not mean the terrestrial biosphere but rather means the whole of the universe, we may well yet see the cohort of complexities associated with human beings repeated elsewhere, though we have to scale up our perspective, just as with scaling up island biography until it coincides with astrobiology. Metrics appropriate to human activity in a terrestrial context will not be sufficient for human (or, more generally, intelligent) activity in an extraterrestrial context. Another way to understand this is that, confined to the surface of Earth, distinctions that would be significant to civilization are conflated by contingent circumstances; raised off the surface of the Earth, and given energy and resources almost without limit, previously conflated properties of civilization manifest themselves in an extraterrestrial context and eventually become obvious as spacefaring civilizations undergo rapid adaptive radiation and come to exemplify different civilizational properties.

Terrestrial civilizations from an extraterrestrial perspective appear homogenous, but this may be a function of their being subject in common to specific terrestrial selection pressures.

Terrestrial civilizations from an extraterrestrial perspective appear homogenous, but this may be a function of their being subject in common to specific terrestrial selection pressures.

But to return to the idea that technology is the pursuit of biology by other means, as I observed in my Centauri Dreams post, How We Get There Matters, existential ends are not indifferent to technological means. In the particular case of the pursuit of biological ends by technological means, this provides a context for thinking about astrobiology in an age of spacefaring civilizations.

starship classes

Many metrics have been proposed for spacefaring civilization. I mentioned some of these in my last post, Thinking about Civilization, including metrics that I have myself attempted to work out. In that post I did not mention the metric that I proposed in my Centuari Dreams post How We Get There Matters (and which I followed with SETI Under Conditions of Constraint for Spacefaring Civilization), which concerned classes of starships. This is a metric immediately relevant to the question of spaceflight understood as the development of a continuum that begins with the first wind-blown distribution of seeds and spores, and which might some day mean the greening of the galaxy.

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Grand Strategy Annex

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Orders, Stages, and Waves


Theoretical Frameworks for Civilization


The problem of an adequate conceptual framework (or, if you prefer, a theoretical or analytical framework) for civilization is simply the problem of how to think about civilization. It is my ambition not merely to think about civilization, but to do so well, i.e., clearly and rigorously, and, to that end, to think about civilization scientifically and philosophically. We need a scientific body of knowledge about civilization, and then a philosophical analysis of this body of scientific knowledge, before we can say that we are capable of thinking about civilization clearly and rigorously.

In my attempt to arrive at a scientific conception of civilization I have formulated many different conceptual frameworks — many of them mere fragmentary ideas without much connection to a wider scientific context, such as in the established social sciences — that I view as something like exercises or experiments, to be tested against the historical record, and also to be extrapolated into the future. Following Carnap’s tripartite distinction of scientific concepts into the taxonomic, the comparative, and the quantitative (cf. The Future Science of Civilizations), some of these ideas are taxonomic, some are comparative, and some are quantitative.

Rudolf Carnap's account of scientific concepts from his Philosophical Foundations of Physics.

Rudolf Carnap’s account of scientific concepts from his Philosophical Foundations of Physics.

Taxonomic, comparative, and quantitative conceptions of civilization

Implicitly I have been employing a taxonomy of civilizations when I used terms such as agrarian-ecclesiastical civilization or industrial-technological civilization, and recently I have suggested that these taxa may be placed within more general taxa. For example, classical antiquity and medieval Europe were both civilizations with an agricultural base, but profoundly different in other respects. Thus if we understand that industrial-technological civilization is a scientific civilization, we can see by analogy how this civilization might be superseded by another kind of scientific civilization but which was not an industrial-technological civilization (cf. David Hume and Scientific Civilization and The Relevance of Philosophy of Science to Scientific Civilization).

In Comparative Concepts in the Study of Civilization I sketched out some of the problems of employing comparative conceptions of civilization, which are of great utility despite the moral repugnance in which such comparisons are held today. Comparative concepts remain underdeveloped because of the moral opprobrium attached to explicit comparisons among civilization, which imply explicit rankings, such as “better than” or “worse than,” “higher” or “lower,” “more advanced” or “less advanced,” “more developed” or “less developed.” Even when rankings of civilizations are carefully and tightly circumscribed so to not to judge the worth of a civilization — presumably its contribution to human history — such rankings are still routinely misconstrued, often willfully so. Even to suggest such a thing is to invite hostile criticism.

There are a number of well-known quantitative schemes for taking the measure of civilization, most especially the Kardashev rankings of Type I, Type II, and Type III (subsequently extrapolated by several authors to both higher and lower types). I wrote about Kardashev’s types at some length in What Kardashev Really Said on Centauri Dreams, so I will not repeat that analysis here. My dissatisfaction with Kardashev types led me to formulate a series of stages in the development of spacefaring civilization, which I wrote about in Beyond the Kardashev Scale and which I spoke about at the first 100YSS event 2011, and then put in essay form in The Moral Imperative of Human Spaceflight.

In brief, I treated the stages of spacefaring civilizations in terms of technological ability to overcome gravitational thresholds. These gravitational thresholds ascend from the surface of Earth (as, i.e., the difficulty of crossing mountain ranges) through planets, stars, and galaxies to the multiverse:

● Stage 0 spacefaring civilizations, or a planet-bound civilizations, have no capacity for spaceflight. (Pre-Sputnik civilization)

● Stage 1 spacefaring civilizations have the kind of minimal capacity that we now possess to loft satellites and human beings into orbit, and even to visit nearby heavenly bodies such as the moon. (Sputnik and after)

● Stage 2 spacefaring civilizations might be defined as those that have established a permanent, self-sustaining presence off the surface of the world of a given civilization’s biological origin. This could also be defined in terms of practical, durable, and routine inter-planetary travel. This is the minimal level of civilization to assure long-term survivability.

● Stage 3 spacefaring civilizations would have achieved practical, durable, and routine interstellar travel.

● Stage 4 spacefaring civilizations would be defined in terms of practical, durable, and routine inter-galactic travel.

● Stage 5 spacefaring civilizations would be defined in terms of practical, durable, and routine travel in the multiverse, i.e., beyond the known universe defined by the consequences of the big bang and observational cosmology.

I conceived my above schema of stages in the development of spacefaring civilization in terms of transportation — whether by foot, canoe, horseback, sail, rail, aircraft, or spacecraft, because it is by such means that human beings came to inhabit the world entire, and by such means that civilizations have spread — but I now see that transportation is a special case of change, and that some similar schema, generalized to address all forms of civilizational change, might be employed. Recently I have been experimenting with several different schematic formulations of change based on a generalization of the stages of spacefaring civilization. Since civilization is, roughly, about large scale social organization, the idea of demographically significant change is central to my formulation. Here is one delineation of stages based on any change whatsoever:

● Stage 0: Equilibrium No change; equilibrium state.

● Stage 1: Firsts Symbolic firsts that are demographically insignificant but mark a possible trajectory for change.

● Stage 2: Growth Building on symbolic firsts, gradual (arithmetical) increase in demographic significance.

● Stage 3: Inflection Passing a threshold at which demographically significant change occurs exponentially (geometrically).

● Stage 4: Predominance At predominance the change is now the norm; a corner has been turned, and the completion of the change is now only a matter of time.

● Stage 5: Integration Full integration. The trajectory of change has been fulfilled, and full integration eventually becomes indistinguishable from an equilibrium state, or Stage 0. This new equilibrium is a more comprehensive state if the change involved growth, and a less comprehensive state if the change involved contraction.

In this schema I assume that growth could be arrested at any stage, and that it can be reversed. The growth of a pandemic that does not kill the host species may reach an inflection point or demographic predominance, but “integration” would mean the pandemic had achieved totality, at which point this would result in the death of the host. The first summit of Mount Everest has been followed by growth in the number of climbers, but this growth will never reach integration because there will not be a time in human history when the whole of humanity has climbed Everest. However, the growth of agricultural civilization very nearly did reach totality as almost all practicable arable land had been brought under cultivation by the time the industrial revolution occurred and a new form of civilization began to take shape.

This is an admittedly imperfect attempt to provide a structure for describing large-scale change of the kind that results in the emergence, growth, decay, or death of a civilization.


Cluster and Series

In a couple of recent posts — The Philosophical Basis of Islamic State and The Seriation of Western Civilization — I have mentioned that I think about the origins of civilization in terms of clusters and series. A cluster is a geographical (or synchronic) conception, while a series is an historical (or diachronic) conception. (Earlier in Synchronic and Diachronic Approaches to Civilization I had made the synchronic/diachronic distinction without relating this to the ideas of cluster and series.)

While I conceived clusters and series of civilizations in terms of the origins of civilization, the ideas could just as well be applied later in the development of civilization, if some new cluster could emerge. Since human civilization at present, however, already covers the entire planet, there are no opportunities for civilizations to originate de novo (on Earth’s surface). One could identify clusters and series of the origins of kinds of civilization (which requires a taxonomy of civilization), so that when industrial-technological civilization begins to emerge in the late eighteenth century, western Europe is the cluster for the origin of this kind of civilization, and from this cluster several diachronic series can be traced. More interesting in my view is to pull back our perspective and to consider the large-scale structure of civilization in the universe. From this perspective, we would speak of a terrestrial cluster, and as various terrestrial civilizations achieve spacefaring status each of these civilizations deriving from the terrestrial cluster would constitute a civilizational series, from which a seriation of spacefaring civilizations would follow.

Initially separate clusters, such as those that constituted the origins of civilization, or, later, the emergence of a new kind of civilization, grow together over time (what Whitehead would have called concrescence), and the growing together of originally separate civilization arguably results in a new cluster. At the present time of planetary civilization, this cluster is the terrestrial cluster. However, we can identify earlier instances when originally separate civilizations grew together, and many of these are marked by great ages of syncretism, which have arguably created some of the greatest symbols of civilization in terms of monumental architecture.

I have not yet made any systematic effort to relate these ideas of cluster and series to taxonomic, comparative, and quantitative concepts of civilization, but have employed the ideas opportunistically as they could be used to illuminate a particular problem. There are many possible ways to bring these ideas together.


The orders of civilization

Another partial conceptual framework that I have worked out for civilization is a hierarchical structure that I call the orders of civilization. These orders are as follows:

● Civilization of the Zeroth Order is the order of prehistory and of all human life and activity and comes before civilization in the strict sense.

● Civilization of the First Order are those socioeconomic systems of large-scale organization that supply the matter upon which history works; in other words, the synchronic milieu of a given civilization, a snapshot in time.

● Civilization of the Second Order is an entire cycle of civilization, from birth through growth to maturity and senescence unto death, taken whole. (Iterated, civilization of the second order is a series, as described above.)

● Civilization of the Third Order is the whole structure of developmental stages of civilization such that any particular civilization passes through, but taken comprehensively and embracing all civilizations within this structure and their interactions with each other as the result of these structures. (Clusters and series are part of the overall structure of civilization of the third order.)

This framework was primarily intended to clarify exactly what we are referring to when we invoke “civilization,” and in a sense it builds upon one of the earliest problems I took up in this blog, which I originally called The Phenomenon of Civilization, i.e., the attempt to speak about civilization as such, without referring to any particular civilization.

Notice that for every order of civilization, we can talk about one and the same civilization from these several points of view, i.e., given civilization CIVx, there is CIVx of the zeroth order, before and outside this civilization, CIVx of the first order, which is some contemporaneous snapshot of its structures, CIVx of the second order, which is the entire narrative of this civilization, and CIVx of the third order, which is the same civilization taken in the context of the life cycles of all civilizations, as one thread in a tapestry of civilization. In this context civilization can be treated formally, as any civilization could be substituted for CIVx.

Again, I have not made a systematic effort to unify these various theoretical frameworks, so that orders of civilization are precisely defined in relation to stages or clusters and series, but there are interesting ways to do this. Civilization of the second order, placed end to end, constitutes a series, while clusters and series are part of the overall structure of civilization of the third order; civilization of the third order is closest to what I previously called the phenomenon of civilization.


Orders, stages, and waves

Orders of civilization as I conceived them do not stand in isolation, but are part of a series of concepts — orders, stages, and waves — intended to offer an increasingly finely-grained account of civilization as one delves into the details of the seriation of civilizations. To a certain extent, then, my conception of the stages of spacefaring civilization mentioned above was intended from the first to be integrated into this model.

When I spoke at the second 100YSS in 2012 I had progressed farther on my typology of stages of spacefaring civilization, and had subdivided stages into waves of expansion (or contraction) — cf. my contribution to 100 Year Starship 2012 Symposium Conference Proceedings, “The Large-Scale Structure of Spacefaring Civilizations.” A wave of expansion that consolidates the achievement of a stage takes different forms depending on the technology available (because how we get there matters) and the strategy of implementing that technology in practice. At that time I distinguished between an incremental outward push in which the farthest regions are last to be inhabited and populations build up first closest to the center from which expansion starts and then later moves into the periphery, and a sudden “moon shot” outward jump (akin to what a biogeographist would call a “sweepstakes dispersal route”) in which the far frontier receives the brunt of the demographic impact, and it is only later with subsequent waves that the buffer between center and periphery is filled in. Needless to say, all of this can also be run backward in order to describe the collapse of civilization.

It will be obvious that these three concepts — orders, stages, and waves — were intended to be integrated into my conception of spacefaring civilizations distinguished according to gravitational thresholds attained. However, as noted above, expansion into space can be re-conceived more generally as any kind of change. Can the conceptual framework of cluster and series be fitted into the framework or orders, stages, and waves, or vice versa? I have integrated a more-or-less intuitive distinction between center and periphery into this model, as the various possibilities for civilizational expansion or retrenchment can be described in terms of the interplay between the center and the periphery of a given civilization. (Earlier I discussed the center/periphery dialectic in The Farther Reaches of Civilization.) This suggests that a place could also be made for clusters and series, which is a pretty elementary idea.

At one time I saw the analysis of civilization in terms of orders, stages, and waves to be the primary theoretical framework I would employ (I even began to assemble a PowerPoint presentation based on this framework, assuming that I would give a talk about it at some point), but I have been working on another framework that supersedes this (and hopefully resolves some of the problems with that schema) and which I hope to soon present in a systematical exposition. However, I tend to let ideas gestate for a long time before I write about them, so it may not be as soon as I hope that I write about it.



Any conclusions could only be provisional at best. As I noted above in the introduction, I consider all of these ideas to be experiments. Sometimes one idea fits a circumstance well, so I make use of it, while on another occasion that idea may not work, but another does. Each unique set of historical circumstances seems to call for a unique theoretical framework, but, of course, the challenge is to find a framework that works well generally to elucidate a wide variety of distinct civilizations. Such a framework could then with greater confidence be projected into the future and give us a glimpse of the shape of structure of civilization to come.

My views continue to evolve and I continue to formulate new concepts and frameworks. As I noted above, I am actively working an an alternative taxonomy that I hope will be more sophisticated and open to the degree of elaboration that would make it applicable not only to the past, but also to the future.

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Grand Strategy Annex

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What is astrobiology?

I suppose that “astrobiology” could be called one of those “ten dollar” words, but despite being a long word of six syllables and a dozen letters, it can be defined quite simply.

Astrobiology has been called, “The study of life in space” (Mix, Life in Space: Astrobiology for Everyone, 2009) and that, “Astrobiology… removes the distinction between life on our planet and life elsewhere.” (Plaxco and Gross, Astrobiology: A Brief Introduction, 2006). Taking these sententious formulations of astrobiology as the study of life in space, which removes the distinction between life on our planet and life elsewhere, together gives us a new perspective with which to view life on Earth (and beyond).

There are, of course, longer and more detailed definitions of astrobiology. There are two in particular that I have cited in previous posts:

“The study of the living universe. This field provides a scientific foundation for a multidisciplinary study of (1) the origin and distribution of life in the universe, (2) an understanding of the role of gravity in living systems, and (3) the study of the Earth’s atmospheres and ecosystems.”

from the NASA strategic plan of 1996, quoted in Steven J. Dick and James E. Strick, The Living Universe: NASA and the Development of Astrobiology, 2005


“Astrobiology is the study of the origin, evolution, distribution, and future of life in the universe. This multidisciplinary field encompasses the search for habitable environments in our Solar System and habitable planets outside our Solar System, the search for evidence of prebiotic chemistry and life on Mars and other bodies in our Solar System, laboratory and field research into the origins and early evolution of life on Earth, and studies of the potential for life to adapt to challenges on Earth and in space.”

from the NASA astrobiology website

I cited these two definitions of astrobiology from NASA in Eo-, Eso-, Exo-, Astro- and other posts in which I used parallel formulations to define astrocivilization.

Learning to take the astrobiological point of view

I‘ve posted a couple remarks about astrobiology on Twitter that I would like to repeat here to set the tone for what follows. More than two years ago I posted this on Twitter:

Astrobiology is island biogeography writ large.

This is one of the few “tweets” I’ve written that was “re-tweeted” multiple times (I’m not very popular on Twitter.) After I wrote this I began a more extensive blog post on this theme, but didn’t finish it; the topic rapidly became too large and started to look like a book rather than a post. Then last month I posted this on Twitter:

In the same way that Darwin provided a new perspective on life, astrobiology provides a novel perspective that allows us to see life anew.

Recently I’ve also been referring to astrobiology with increasing frequency in my blog posts, and I referenced astrobiology in my 2012 presentation at the 100YSS symposium in Houston and just last month in my presentation at the Icarus Interstellar Starship Congress in Dallas.

It will be apparent to the reader, then, then the idea of astrobiology has been slowly growing on me for the past few years, and the more I think about it, the more I come to realize the fundamentally new perspective that astrobiology offers on life and its evolution. Moreover, astrobiology also is suggestive for the future of life, and what we will discover about life the more we explore the cosmos.

Astrobiology: the Fourth Revolution in the Life Sciences

The more I think about astrobiology, the more I realize that, like earlier revolutions in the life sciences, the astrobiological point of view gives a novel perspective on familiar facts, and in so doing it potentially orients science in a new direction. For this reason I now see astrobiology as the fourth of four revolutions that instantiated the life sciences in their present form and continue to shape the way that we think about biology and the living world.

Here is my list of the four major revolutions in biological thought that have shaped the life sciences:

● Natural selection Independently discovered by Charles Darwin and Alfred Russel Wallace, natural selection gave sharpness of focus to many vague evolutionary ideas that were being circulated in the nineteenth century. With natural selection, biology had a theory by which to work, that could unify biological thought in a way that had not previously been possible. Of the Darwinian revolution Harald Brüssow wrote, “How can biologists cope conceptually and technically with this enormous species number? A deep sigh of relief came for biologists already in 1859 with the publication of Charles Darwin’s book ‘On the Origin of Species’. Suddenly, biologists had a unifying theory for their branch of science. One could even argue that the holy grail of a great unifying theory was achieved by Darwin and Wallace at a time when Maxwell was unifying physics, the older sister of biology, at the level of the electromagnetic field theory.” (“The not so universal tree of life or the place of viruses in the living world” Phil. Trans. R. Soc. B, 2009, 364, 2263–2274)

● Genetics After Darwin and Wallace came Gregor Mengel, who solved fundamental problems in the theory of inheritance and so greatly strengthened the Darwinian theory of descent with modification. As Darwin had provided the mechanism for the overall structure of life, Mendel provided the mechanism that made natural selection possible. Mendel’s work, contemporaneous with Darwin, was forgotten and not rediscovered until the early twentieth century. It was not until the middle of the twentieth century that Crick and Watson were able to delineate the structure of DNA, which made it possible to describe Mendelian genetics on a molecular level, thus making possible molecular biology.

● Evo-devo Evo-devo, which is a contraction of evolutionary developmental biology, once again went back to the roots of biology (as Darwin had done by formulating a fundamental theory, and as Mendel had done by his careful study of inheritance in pea plants), and returned the study of embryology to the center of attention of evolutionary biology. Studying the embryology of organisms with the tools of molecular biology gave (and continues to give) new insights into the fine structure of life’s evolution. Before evo-devo, few if any suspected that the homology that Darwin and others notes on a macro-biological scale (the structural similarity of the hand of a man, the wing of a bat, and the flipper of a dolphin) would be reducible to homology on a genetic level, but evo-devo has demonstrated this in remarkable ways, and in so doing has further underlined the unity of all terrestrial life.

● Astrobiology Astrobiology now lifts life out of its exclusively terrestrial context and studies life in its cosmological context. We have known for some time that climate is a major driver of evolution, and that climatology is in turn largely driven by the vicissitudes of the Earth as the Earth orbits the sun, exchanges material with other bodies in our solar system, and the solar system entire bobs up and down in the plane of the Milky Way galaxy. Of understanding of life gains immensely by being placed in the cosmological context, which forces us both to think big, in terms of the place of life in the universe, as well as to think small, in terms of the details of origins of life on Earth and its potential relation to life elsewhere in the universe.

This is obviously a list of revolutions in biological thought compiled by an outsider, i.e., by someone who is not a biologist. Others might well compile different lists. For example, I can easily imagine someone putting the Woesean revolution on a short list of revolutions in biological thought. Woese was largely responsible for replacing the tripartite division of animals, plants, and fungi with the tripartite division of the biological domains of Bacteria, Archaea and Eukarya. (There remains the question of where viruses fit in to this scheme, as discussed in the Brüssow paper cited above.)

tree-of-life 2

Since I have included molecular phylogeny among the developments of evo-devo (in the graphic at the bottom of this post), I have implicitly place Woese’s work within the evo-devo revolution, since it was the method of molecular phylogeny that made it possible to demonstrate that plants, animals and fungi are all closely related biologically, while the truly fundamental division in terrestrial life is between the eukarya (which includes plants, animals, and fungi, which are all multicellular organisms), bacteria, and archaea. If any biologists happen to read this, I hope you will be a bit indulgent toward my efforts, though I certainly encourage you to leave a comment if I have made any particularly egregious errors.

Toward a Radical Biology

Darwin mentioned the origins of life only briefly and in passing. There is the famous reference to, “some warm little pond with all sorts of ammonia and phosphoric salts, — light, heat, electricity &c. present” in his letter to Joseph Hooker, and there is the famous passage at the end of his Origin of Species which I discussed in Darwin’s Cosmology:

“Thus, from the war of nature, from famine and death, the most exalted object which we are capable of conceiving, namely, the production of the higher animals, directly follows. There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.”

Darwin, of course, had nothing to go on at this point. Trying to understand or explain the origins of life without molecular biology would be like trying to explain the nature of water without the atomic and molecular theory of matter: the conceptual infrastructure to circumscribe the most basic elements of life did not yet exist. (The example of trying to define water without the atomic theory of matter is employed by Robert M. Hazen in his lectures on the Origins of Life.)

Just as Darwin pressed biology beyond the collecting and comparison of beetles in the backyard, and opened up deep time to biology (and, vice versa, biology to deep time), so astrobiology presses forward with the project of evolutionary biology, pursuing the natural origins of life to its chemical antecedents. Astrobiology is a radical biology in the same way that Darwin was radical biology in his time: both go to the root to the matter to the extent possible given the theoretical, scientific, and technological parameters of thought. It is in the radical sense that astrobiology is integral with origins of life research; it is in this sense in which the two are one.

The humble origins of radical ideas

The radical biology of Darwin did not start out as such. In his early life, Darwin considered becoming a country parson, and when Darwin left on his voyage on the Beagle as Captain Fitzroy’s gentleman companion, he held mostly conventional views. It is easy to imagine an alternative history in which Darwin retained his conventional views, went on to become a country parson, and gave Sunday sermons that were mostly moral homilies punctuated by the occasional quote from scripture the illustrate the moral lesson with a story from the tradition he nominally represented. Such a Darwin from an alternative history would have continued to collect beetles during the week and would have maintained his interest in natural history.

Just as Darwin came out of the context of English natural history (which, before Darwin, gave us those classic works of teleology, Paley’s Natural Theology and Chambers’ Vestiges of the Natural History of Creation — a work that the young Darwin greatly admired), so too astrobiology comes out of the context of a later development of natural history — the scientific search for the origins of life and for extraterrestrial life. While the search for extraterrestrial life is “big science” of an order of magnitude only possible by an institution like NASA, in this respect it stands in the humble tradition of natural history, since we must send robots of Mars and the other planets until we can go there ourselves with a shovel and rock hammer. From such humble beginnings sometimes emerge radical consequences.

I think we are already beginning to see the potentially radical character of astrobiology, and that this development in biology promises a paradigm shift almost of the scope and magnitude of natural selection. Indeed, both natural selection and astrobiology can be understood as further (and radical) contextualizations of the theme of man’s place in nature. When Darwin wrote, he contextualized human history in the most comprehensive conception of nature then possible; today astrobiology must contextualize not only human history but also the totality of life on Earth in a much more comprehensive cosmological context.

As our knowledge of the world (which was once very small, and very parochial) steadily expands, we are eventually forced to extend and refine our concepts in order to adequately account for the world that we now know. Natural selection and astrobiology are steps in the extension and refinement of our conception of life, and of the place of life in the world. Life simpliciter is, after all, a “folk” concept. Indeed, “life” is folk biology and “world” is folk cosmology. Astrobiology brings together these folk concepts and attempts to bring scientific rigor to them.

The biology of the future

Astrobiology is laying the foundations for the biology of the future. Here and now on earth, without having surveyed life on other worlds, astrobiologists are attempting for formulate concepts adequate to understanding life at the largest and the smallest scales. Once we take these conceptions along with us when we eventually explore alien worlds — including alien worlds close to home, such as Mars and the ocean beneath the ice of Europa — it is to be expected that further revolutions in the life sciences will come about as a result of attempting to understand what we eventually find in the light of the concepts we have preemptively developed in order to understand biology beyond the surface of the Earth.

Future revolutions in biology will likely have the same radical character as natural selection, genetics, evo-devo, and astrobiology. Future naturalists will do what naturalists do best: they will spend their time in the field finding new specimens and describing them for science, and in the process of the slow and incremental accumulation of scientific knowledge new ideas will suggest themselves. Perhaps someone laid low by some alien fever, like Wallace tossing and turning as he suffered from a fever in the Indonesian archipelago, will, in a moment of insight, rise from their sick bed long enough to dash off a revolutionary paper, sending it off to another naturalist, now settled and meditating over his own experiences of new and unfamiliar forms of life.

The naturalists of alien forms of life will not necessarily have the same point of view as that of astrobiologists — and that is all to the good. Science thrives when it is enriched by new perspectives. At present, the revolutionary new perspective is astrobiology, but that will not likely remain true indefinitely.

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four revolutions

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Grand Strategy Annex

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