adaptationism fails to resolve fermi’s paradoxsaj.matf.bg.ac.rs/170/pdf/089-100.pdf ·...

Serb. Astron. J. } 170 (2005), 89 - 100 UDC 52–37Original scientific paper

ADAPTATIONISM FAILS TO RESOLVE FERMI’S PARADOX

M. M. Cirkovic1, I. Dragicevic2 and T. Beric-Bjedov2

1Astronomical Observatory, Volgina 7, 11160 Belgrade 74, Serbia and Montenegro

2Faculty of Biology, University of Belgrade,Studentski trg 3, 11000 Belgrade, Serbia and Montenegro

(Received: March 21, 2005; Accepted: April 12, 2005)

SUMMARY: One of the most interesting problems in the nascent disciplineof astrobiology is more than half-century old Fermi’s paradox: why, consideringextraordinary young age of Earth and the Solar System in the Galactic context, don’twe perceive much older intelligent communities or signposts of their activity? Inspite of a vigorous research activity in recent years, especially bolstered by successesof astrobiology in finding extrasolar planets and extremophiles, this problem (alsoknown as the ”Great Silence” or ”astrosociological” paradox) remains as open asever. In a previous paper, we have discussed a particular evolutionary solutionsuggested by Karl Schroeder based on the currently dominant evolutionary doctrineof adaptationism. Here, we extend that discussion with emphasis on the problemssuch a solution is bound to face, and conclude that it is ultimately quite unlikely.

Key words. Astrobiology – Extraterrestrial inteligence

When the stars were right, They couldplunge from world to world through thesky; but when stars were wrong, Theycould not live.

Howard P. Lovecraft (1928)

How can one hide from that which neversets?

Heraclitus of Ephesus (cca. 550 BC)

1. INTRODUCTION: FERMI’SPARADOX AND ASTROBIOLOGY

In a previous paper (Cirkovic 2005), we havedescribed an interesting solution of Fermi’s para-dox1, proposed in a qualitative form by the Canadiannovelist Karl Schroeder in his recent novel Perma-nence (Schroeder 2002), based among other thingsupon previous speculations of Raup (1992), Lipunov(1997), and others. Urban legend (corroborated byhistorical research; see Jones 1985) has it that thegreat Italian physicist Enrico Fermi at dinner withEmil Konopinski, Edward Teller, and Herbert York,about 1950, asked ”Where are they?” in reference

1It would be most appropriate to call it Tsiolkovsky-Fermi-Viewing-Hart-Tipler’s paradox (for much of the history, see Webb2002; see also Lipunov 1997). We shall use the locution ”Fermi’s paradox” for the sake of brevity, but with full respect forcontributions of the other important authors. Also known as the ”Great Silence” (Brin 1983) or ”astrosociological” paradox(Gindilis and Rudnitskii 1993).

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M.M. CIRKOVIC, I. DRAGICEVIC and T. BERIC-BJEDOV

to extraterrestrial visitors. The question belies aprofound understanding of the spatial and temporalscales of our universe. Even going at a fraction of thespeed of light, the time it would take to cross galacticdistances is small compared to the age of the Galaxy.Thus, the presumed fact that there are no extrater-restrials in the Solar System—neither now nor in ourpast light cone—requires an explanation. To this,we can today add the absence of extraterrestrial in-telligent manifestations detectable by modern as-tronomical instruments, like Dyson shells2 or tracesof burning antimatter fuel (Jugaku and Nishimura2003, Harris 2002). Hereby, we consider the adapta-tionist solution in some more detail and attempt toelaborate its weaknesses.

Before we briefly review the adaptationist so-lution to Fermi’s paradox, a word about the con-ceptual importance of this topic for biological sci-ence may be in order. In an interesting debate, thephilosopher of biology Eliot Sober has argued thatthe deployment of multiple radical/controversial hy-potheses is in itself an adaptive strategy in thescientific domain (Sober 1994). He makes the con-vincing case that early commitment to the reality oftheoretical constructs allows science to flourish. Thisis particularly interesting in the context of the rel-ative primacy of physics among the sciences in thelast century: giants of the XX century physics werepeople who were bold to put forward ideas not suf-fering, to paraphrase Niels Bohr’s famous rebuttal,from ”insufficient craziness”. With exactly this leit-motif in mind, we approach the present topic andproblems in astrobiology in general. Astrobiologyis, admittedly, still in its infancy as a scientific disci-pline. However, it seems natural to try to investigateextrapolations of our best biological theories to en-compass larger and larger, as well as more diversehabitats. Astrobiology is, as several authors have re-cently emphasized (e.g. Des Marais and Walter 1999,Knoll and Bambach 2000), our best chance of over-coming the ”provincial” (Munson 1975) or ”unfalsi-fiable” (Popper 2002) nature of biology in general,and evolutionary theory in particular. Great mindshave been aware of this for a long time; for instance,Henderson wrote in his classic 1913 monograph TheFitness of the Environment :

The properties of matter and the course ofcosmic evolution are now seen to be inti-mately related to the structure of the livingbeing and to its activities; they become,therefore, far more important in biologythan has previously been suspected. Forthe whole evolutionary process, both cos-mic and organic, is one, and the biologistmay now rightly regard the Universe in itsvery essence as biocentric.

2. THE ADAPTATIONIST SOLUTION

Let us now briefly review the adaptationist so-lution to Fermi’s paradox. Schroeder starts by crit-icising what he call providential view of life and in-telligence in the universe, which he links to Teillhardde Chardin, but which applies with equal force to anarray of very diverse secular thinkers, from HerbertSpencer to Carl Sagan: view of special properties oflife intelligence which make them in a very tangi-ble sense the ”pinnacle of creation” (either designedor naturalistic), and whose emergence demarkates anew epoch in the overall history of matter in theuniverse. In a simplified rendering, it is easy tosearch for life and intelligence because they are sodifferent from all other phenomena in nature, andthat applies even more forcefully to the tool-makingconsciousness, since it can intentionally influence itsphysical environment. Tool-making consciousness is,according to this view, the basic property of complexinformation-processing entities. This is the view be-hind the SETI projects of today, and much has beenwritten in its favor. But it is far from being limitedto astrobiology: this is also the default attitude ofAI researchers, popular science writers, and most ofthe public perception of the world science unveils inits progress is framed in its terms.

What should we contrast this providentialview of intelligence? Schroeder offers a clever alter-native, which he does not dub, but which we can, forreasons to be shortly described, call adaptationist:

What we found instead was that eventhough a species might remain starfaringfor millions of years, consciousness doesnot seem to be required for toolmaking. Infact, consciousness appears to be a phase.No species we have studied has retainedwhat we could call self-awareness for itsentire history. Certainly none has evolvedinto some state above consciousness. (p.108)

This is the crux of the problem (for the astrobiolo-gist protagonists of Schroeder’s novel; solution for us,wishing to resolve Fermi’s paradox!): our estimatesand expectations of the phenomenon of intelligence—which is, above all, a biological phenomenon—arewrong. Intelligence is significant only insofar as itoffers an evolutionary advantage, a meaningful re-sponse to the selective pressure of the fluctuating en-vironment. Only so far, and no further is the ”selfishgene” willing to carry that piece of luggage.

This approach to explanation in evolution-ary biology is known as adaptationism; its ma-jor proponents being distinguished biologists such asRichard Dawkins and John Maynard-Smith, as wellas contemporary philosophers such as Daniel Den-

2In a prescient 1960 study, Freeman Dyson suggested that the natural course of increase in the power consumption of a tech-nological civilization will lead to its utilizing most of the energy output of its parent star. To that effect, he suggested thatvery advanced societies will build an array of devices surrounding most of its parent star, thus from the outside looking likean (infrared emitting) shell. This idea is in accordance with Kardashev’s concept of the Type II society (Kardashev 1964)and has received many subsequent elaborations (e.g. Badescu 1995).

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nett or Eliot Sobber.3 Adaptation is a trait that hasbeen selected for by natural selection. Adaptationisthypothesis can be conventionally defined as a state-ment that asserts that a given trait in a populationis an adaptation. In other words, natural selectionis the major (if not the sole) cause of presence andpersistence of traits in a given population. The defi-nition of Sober (1993) in his influential book goes asfollows:

Adaptationism: Most phenotypic traits inmost populations can be explained by amodel in which selection is described andnonselective processes are ignored. (p.122)

Examples of adaptationist explanations abound.Camouflage colors of birds and insects, Eskimofaces, two-component spray of the bombardier bee-tle, horns of Ontophagus acuminatus, and myriadsof other observed properties of living beings are in-terpreted as giving their carriers an advantage inthe endless mill of natural selection. Their genesare more likely to propagate along the thousands ofgenerations of natural history. The most extremeversion of adaptationism is sometimes called gene-centrism and is expounded by Richard Dawkins, andneatly encapsulated in the title of his best-sellingbook The Selfish Gene (Dawkins 1989): genes areusing (in a sufficiently impersonal sense of the word,see Ref. 16) organisms to propagate their own copiesas efficiently as possible in time. It may be of histori-cal interest that adaptationism is usually traced backto Alfred R. Wallace, one of the two great biologicalrevolutionaries, who was also one of the forefathersof modern astrobiology with his intriguing and re-markably prescient book Man’s Place in the Universe(Wallace 1903).

Fig. 1. Adaptationist solution to Fermi’s paradoxschematized. Switching to technological adaptation isnecessarily followed by reverting to simpler, but morestable direct (”post-technological”) adaptation now invarious locales. Just as technological adaptation canbe thought of as intentional development of charac-ters mimicking and improving certain adaptive traitsfound in nature, the direct adaptation during the re-version phase can be described as appearance of traitsmimicking some features of technology.

The adaptationist view is the scientific foun-dation of Schroeder’s solution to Fermi’s paradox.Intelligence is an adaptive trait, like any other.Adaptive traits are bound to disappear once theenvironment changes sufficiently for any selectiveadvantage which existed previously to disappear.4

However, tool-making (technological) capacities ofadvanced intelligent communities actively influencetheir environment, and decrease selective pressure(”flattening” the fitness landscape, to use the popu-lar evolutionary picture). In the long run, the intel-ligence is bound to disappear, as its selective advan-tage is temporally limited by ever-changing physicaland ecological conditions. In Schroeder’s words:

Look at crocodiles. Humans might moveinto their environment— underwater inswamps. We might devise all kinds of so-phisticated devices to help us live there, orartificially keep the swamp drained. Butdo you really think that, over thousandsor millions of years, there won’t be po-litical uprisings? System failures? Re-ligious wars? Mad bombers? The in-stant something perturbs the social sys-tems that’s needed to support the tech-nology, the crocodiles will take over again,because all they have to do to survive isswim and eat... It’s the same with con-sciousness. We know now that it evolvesto enable a species to deal with unforeseensituations. By definition, anything we’vemastered becomes instinctive. Walking isnot something we have to consciously thinkabout, right? Well, what about physics,chemistry, social engineering? If we haveto think about them, we haven’t masteredthem—they are still troublesome to us. Aspecies that succeeds in really masteringsomething like physics has no more needto be conscious of it. Quantum mechanicsbecomes an instinct, the way ballistics al-ready is for us. Originally, we must havehad to put a lot of thought into throw-ing things like rocks or spears. We even-tually evolved to be able to throw with-out thinking— and that is a sign of thingsto come. Some day, we’ll become... ableto maintain a technological infrastructurewithout needing to think about it. With-out need to think, at all...

This chain of events is schematically shown in Fig. 1.An intelligent species can last long in the state of di-rect adaptation to their environment on the homeplanet (local)—several hundred thousand years inthe case of homo sapiens sapiens. A rather fasttransition from direct to technological adaptationcorresponds to building of a technical civilization,this crucial ingredient of all SETI studies. But thestage of technological adaptation, distributed all overthe various planets, is inherently less stable. In along run, it will tend to pass into a state of frag-mented habitats reverting to direct biological adap-

3For some of the many contemporary reviews, see Larson (2004), Tucic (2004), Gould (2002), Wallace (2004).

4The may get exapted (Gould and Vrba 1982, Gould 2002), i.e. get to be used for a purpose different from the original one.However, this does not seem relevant for the present purpose, since it is hard to imagine intelligence or tool-making capacitybecoming exaptations on the biological (and not cultural) level.

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tation (”crocodiles returning”). The second transi-tion is much slower and might be occassionally in-terrupted or arrested; yet, the general trend towardreturn to direct adaptation is inescapable. This bi-furcation is, in this view, tantamount to extinctionof the original intelligent species, and its remains aregradually submerged into the general astrobiologi-cal ”noise” of the Galaxy. The transient nature ofthe phase of technological adaptation constitutes thebulk of the ”Great Filter” explaining the silentiumuniversi. A colorful metaphor of the rise and fallof such advanced technological communities can befound, for instance, in a piece of the 1967-68 wood-cut Metamorphosis III by great M. K. Escher (Fig.2).

Fig. 2. A metaphor of the adaptationist solution toFermi’s paradox: emergence of complexity crownedby society (of social insects!) from the simple pat-tern, followed by reverting to simpler, but more sta-ble forms (imagine the time flowing along the addedhorizontal axis). This is a section from the three-color woodcut Metamorphosis III which Escher fin-ished (after considerable delays and even reluctance,as described in his diaries) in 1968. The metaphoris limited by the fact that the final state of the di-rect adaptation is not the mirror-image of the orig-inal pre-intelligence state (”evolution doesn’t repeatitself”).

Ironically enough, the application of adapta-tionism to Fermi’s paradox has some similarities withthe old biological heresy of orthogenesis, histori-cally the major rival to Darwinism on the oppositeside of the functionalism/formalism divide (Gould2002, Tucic 2004, Larson 2004). It was championedduring roughly 1870-1950 by distinguished natural-ists like Hyatt, Haacke, Cope, Eimer, Whitman, andSchindewolf. Darwin himself called it rather dismis-sively (but very aptly from the present point of view!)”Descent-theory” in the beginning, and Schindewolfcalled it typostrophism in its last blossom, but itamounts to the same idea: a global morphologicaltype of a species (or a higher taxon in some ver-sions) contains big, but ultimately finite, potentialfor variation. This pool of possibilities will be man-ifested through one or more internal channels whichdirect evolution of a species from its beginning to in-evitable end. Contra Darwin and subsequent adap-

tationists, orthogeneticists believed that variation isnot isotropic and although they did allow for nat-ural selection shaping some of the traits of species,the highest relative frequency must be ascribed tothe directional change along the preset channels ofa given, discrete morphological form. Famous ex-amples of orthogenesis included those cases whereevolution clearly led organisms toward extinction bymechanical continuation of unadaptive traits: ever-increasing teeth of saber-tooth cats which, after pass-ing through some optimum size, clearly impeded ef-ficiency of their feeding. The choice and nature ofthese orthogenetic channels differed from author toauthor, but most XX century orthogeneticists foundthem in the laws of embryological development, no-tably the (in)famous biogenetic law of Ernst Haeckel.Another aspect of orthogenesis, however, is interest-ing from the present point of view. In one of the his-torically last serious analysis of orthogenesis, Grene(1958) writes on Schindewolf’s typostrophism:

Furthermore, Schindewolf agrees with theolder paleontologists that within each type,once it had appeared, there is a progres-sive, orthogenetic development. In fact,there is a rhythm analogous to that ofbirth, maturation, and senescence: thesudden appearance of a new type, its or-thogenetic advance, and finally a stage ofthe breaking up of types which usuallyleads to extinction. (p. 112)

This presents a strong analogy with the adaptation-ist view of the generic history of tool-making civiliza-tions. How comes, we need to ask, that the applica-tion of the most rigorous functionalist programme,such as adaptationism, leads to a picture so similar tothe one portrayed by eminently formalist view suchas orthogenesis? The answer, one is tempted to con-clude, is that the function/form distinction becomesblurred when it comes to the evolution of culturalconcepts, notably technology. We may find a cluein the functionalism itself; as Grene cogently notes,there we perceive

...the ruling passion of Darwinism: [in]the determination not to look at structure.Structure must be explained away ; it mustbe reduced to the conditions out of which itarose rather than acknowledged as struc-ture in itself. (p. 126)

What exactly plays the role of structure (or form)in the case of technological civilization? It seemsthat at least part of that role has to lie with thetechnology itself ; and, indeed, this is what hasalready been either neglected or downplayed bythe ultra-Darwinian adaptationism applied—ratherroughly—to the evolution of humanity (e.g. Wright2000). Thus, treating technology as something mal-leable mainly by external factors and accommodat-ing purely functional needs, leads to something verysimilar to the orthogenetic fatum to which many ofthe historically raised criticisms apply. We shall re-turn to this topic in the subsection dealing with post-biological evolution below.

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3. DIFFICULTIES WITH THEADAPTATIONIST APPROACH

Here we briefly consider some of the objec-tions to the application of adaptationism for solvingFermi’s paradox. Although some of them appearedin the literature in other contexts, none were appliedin this manner, and most of them are new. None ofthese arguments are decisive, but in the young fieldplagued with uncertainties this is not to be expectedeither. Taken together, they strongly indicate that,while undoubtedly adaptationism plays some role inthe overall astrobiological evolution of the Galaxy, itcannot pretend to bona fide resolve Fermi’s puzzlingquestion.

3.1. Cultural and postbiological evolution

In an important recent paper, the distin-guished historian of science Stephen J. Dick arguedthat there is a tension between SETI, as convention-ally understood, and prospects following exponentialgrowth of technology as perceived in recent times onEarth (Dick 2003):

But if there is a flaw in the logic of theFermi paradox and extraterrestrials are anatural outcome of cosmic evolution, thencultural evolution may have resulted in apostbiological universe in which machinesare the predominant intelligence. This ismore than mere conjecture; it is a recog-nition of the fact that cultural evolution– the final frontier of the Drake Equation– needs to be taken into account no lessthan the astronomical and biological com-ponents of cosmic evolution. [emphasis inthe original]

It is easy to understand the necessity of redefiningastrobiological studies in general and our view ofFermi’s paradox in particular in this context: forexample, postbiological evolution makes those be-havioral and social traits like territoriality or ex-pansion drive (to fill the available ecological niche)which are—more or less successfully—”derived fromnature” lose their relevance.

One approach we find promising is the conceptof megatrajectory, introduced by Knoll and Bambach(2000), who cogently argue that astrobiology is theultimate field for confirmation or rejection of our bi-ological concepts. In relation to the old problem ofprogress (or its absence) in the evolution of life onEarth, Knoll and Bambach offer a middle road en-compassing both contingent and convergent featuresof biological evolution through the idea of a mega-trajectory:

We believe that six broad megatrajecto-ries capture the essence of vectorial changein the history of life. The megatrajecto-ries for a logical sequence dictated by thenecessity for complexity level N to existbefore N+1 can evolve... In the view of-fered here, each megatrajectory adds newand qualitatively distinct dimensions tothe way life utilizes ecospace.

The six megatrajectories outlined by the biologicalevolution on Earth so far are, from the origin of lifeto the ”Last Common Ancestor” prokaryote diversi-fication, unicellular eukaryote diversification, multi-cellularity, invasion of the land, and appearance ofintelligence and technology. Postbiological evolutionmay present the seventh megatrajectory, triggered bythe emergence of artificial intelligence at least equiv-alent to the biologically-evolved one, as well as theinvention of several key technologies of the similarlevel of complexity and environmental impact, likemolecular nanoassembling or stellar uplifting.

In other words, it seems necessary to reject aparticular form of inductivist fallacy. As in earliertimes, inductivists argued (when criticized, for in-stance, by Karl R. Popper and others) that it is nat-ural to assume a ”meta-rule” of inference along thelines of ”future will resemble the past”, thus thereis a creeping prejudice that the present and futuremodes of evolution need to be the same as those lead-ing us to the present epoch. This is a consequenceof the (today typical) idolatry of adaptation: almostreflex and non-thinking assumption that any evolu-tion has to be adaptationist (e.g. Dennett 1995).Contra such fashionable views like evolutionary psy-chology/behavioral ecology/sociobiology, there is noreason to believe that all complex living systemsevolve according to the rules of functionalist natu-ral selection, and not, for instance, in a Lamarckian,orthogenetic or saltationist manner. Without enter-ing this excessively complex topic here, we may notethat however we assess our experience with intelli-gence, culture, tool-making and technology, every-thing points that it is non-Darwinian evolution, iffor nothing, then because the vector of change is notisotropic. The inductivist meta-rule has been suc-cessfully relegated to the history of epistemology, butthe prejudice in biology is still very strong, and thatexactly in the time when first serious quantitativemodels of complex cultural evolution begin to ap-pear in the literature (e.g. Fath and Sarvary 2005).

Herein lies one of the weaknesses of adap-tationist solution: there is no proof—or indeed aclear counterargument—that a chain of intentionalstrategies for preventing adaptationist devolutioncould not extend over an arbitrarily long time in thehistory of an advanced civilization. In other words,things certainly can and will go wrong at many lo-cations over a sufficient period of time, but one couldeasily imagine planning and building of ”concentricrings” of safety mechanisms, each projected to beactivated after all previous have failed. Intentional-ity brings an entirely new qualitative angle in thepicture. Each mechanism individually can and willeventually fail in deep time (geological or astrophys-ical), but there seems to be no reason why the entiresystem could not be simply vast enough and contin-uously assembled over time in order to counter thediverging trends of isolation and devolution.

3.2. Right wall of complexity?

Adaptationist solution assumes that the realmof knowledge and phenomenal experiences of ad-vanced intelligent beings is necessarily finite, no mat-

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ter how huge it is. While this may sound inno-cent enough (all meaningful physical quantities, incontrast to mathematical ones, are usually held tobe finite), and even in accordance with the cur-rently fashionable tendencies—at least within phys-ical science—of searching for the ”theory of every-thing”, this assumption is in no way incontrovertible.In other words, and to use another oft-discussed bio-logical metaphor (e.g. Shanahan 1999, Radick 2000,Gould 1996, 2002), adaptationist solution requiresthat besides the left wall of minimal complexity (inthe vicinity of which reside members of the realms ofBacteria and Archea), biological world is necessar-ily limited by the fixed right wall of maximal com-plexity (and we may assume that members of thetransient state of advanced, space-faring technologi-cal species reside just left of this unscaleable barrier).

This concept is suspicious on several grounds.Apart from the possibility of postbiological evolu-tion considered above, and concerns of Knoll andBambach (2000) about repeated scaling of the max-imal complexity within different macroevolutionaryregimes, this form of finitism is under fire in bothmathematical and cosmological domains. Godel’stheorem and subsequent results in the flourishingresearch field of incompleteness and randomness inpure mathematics (e.g. Chaitin 1987), show thateven the most abstract world of mathematical truthis inexhaustible in a very specific and quantitativeway. On the opposite end of the cognitive spectrum,modern cosmology strongly indicates the existenceof some form of the multiverse – the infinite set ofcosmological domains, of which our entire visible uni-verse is just an infinitesimal part (e.g. Linde 1990,Ellis et al. 2004). All this suggests that the domainof knowledge is indeed infinite (while, of course, theactual amount of knowledge at any particular epochis bound to be finite), which would remove a plankfrom the foundations of the adaptationist approach.5

3.3. Mass extinctions – the Galactic variety

What adaptationism fails to explain on Earth,it will fail to explain in the Milky Way. Perhaps theforemost problem with the adaptationist doctrine ascurrently presented by the evolutionary orthodoxy,is its failure to be useful in cases of brief and sud-den episodes in the history of life known as the massextinctions. In the words of Raup’s (1991) colorfulsubtitle, in such difficult times ”luck” is more impor-tant than ”genes”. In our (highly incomplete) fossilrecord, ”Big Five” mass extinction episodes standas the most remarkable features, after the Cam-brian Explosion, of the history of life (e.g. Jablonski1986, Raup 1994, Courtillot 1999, Ward and Brown-lee 2000).

For the present purposes, it is important tounderstand that the fact of mass extinction under-

mines the doctrine of extrapolationism, usually serv-ing to ”fill in the gaps” of the evolutionary record.In famous words of Gould (2002), mass extinctionsare found to be ”more frequent, more rapid, more in-tense, and more different in their effects” than nat-uralists have suspected prior to 1980. Broadeningof the stage of biological research, characteristic forastrobiology, brings new agents of destruction in ad-dition to the ”classical” terrestrial ones (for a pre-

liminary list, see Dragicevic and Cirkovic 2002). No-table (but far from unique!) examples are intermit-tent bursts of high-energy cosmic rays and electro-magnetic radiation of cosmic origin. For instance, ina recent study, Smith et al. (2004) write:

In any case, Mars should have been sub-jected to brief optically thin exposures tosterilizing γ-rays and hard X-rays from so-lar flares, supernovae, and γ-ray burstsmany times during the last Gyr. Similarly,if Mars began with a thick atmosphere,then its early evolution would have beenpunctuated with bursts of UV representingredistributed X-rays from the same astro-nomical sources.

If, as we may have some independent indicationsfrom planetology, Martian conditions are in fact veryfrequent and even more life-conducting than earlyEarth’s, the conclusion that such radiation-drivenextinction events are even more prominent in theoverall history of life in the Milky Way than judgedby the terrestrial record alone seems inescapable. Inother words, astrobiological evolution of the MilkyWay also possesses its ”third tier”, the overarchingglobal level of change (Gould 1985).

The important paper of Annis (1999) opensa new vista in studying Fermi’s paradox byintroducing—though not quite explicitly—the notionof the global regulation mechanism: a dynam-ical process preventing or impeding uniform emer-gence and development of life all over the Galaxy. InAnnis’ model, which he dubbed the phase-transitionmodel for reasons to be explained shortly, the role ofsuch global Galactic regulation is played by gamma-ray bursts (henceforth GRBs), collosal explosionscaused either by terminal collapse of supermassiveobjects (”hypernovae”) or mergers of binary neutronstars. GRBs observed since 1950s have been knownfor almost a decade already to be of cosmological ori-gin, arising in galaxies often billions of parsecs away,and it has been calculated that these are the mostenergetic events in the universe since the Big Bangitself. Astrobiological and ecological consequencesof GRBs and related phenomena have been inves-tigated recently in several studies (Thorsett 1995,Scalo and Wheeler 2002, Smith et al. 2004). To offerjust a flavor of the results, let us mention that Dar(1997) has calculated that the terminal collapse ofthe famous supermassive object Eta Carinae coulddeposit in the upper atmosphere of Earth the en-

5Adaptationist might retort that the amount of useful knowledge will still be finite, and that useless information (like positionsand momenta of molecules in a chunk of gas, or 10100th digit in the decimal expansion of π) does not count. However, thecriterion of usefulness is obviously culture- and circumstance-dependent! While the issue certainly deserves further scrutiny,we feel that the onus of the proof here lies with the finitist.

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ergy equivalent to the simultaneous explosions of 1kiloton nuclear bomb per square kilometer all overthe hemisphere facing the hypernova! Annis sug-gested that GRBs could cause mass extinctions oflife all over the Galaxy (or at least a big part ofit), preventing or arresting the emergence of complexlife forms. Thus, there is only a very small prob-ability that a particular planetary biosphere couldevolve intelligent beings in our past. However, sincethe regulation mechanism exhibits secular evolu-tion, with the rate of catastrophic events decreasingwith time, at some point the astrobiological evolu-tion of the Galaxy will experience a change of regime.When the rate of catastrophic events is high, thereis a sort of quasi-equilibrium state between the nat-ural tendency of life to spread, diversify, and com-plexify, and the rate of destruction and extinctions.When the rate becomes lower than some thresholdvalue, intelligent and space-faring species can arisein the interval between the two extinctions and makethemselves immune (presumably through technolog-ical means) to further extinctions, and spread amongthe stars. Thus the Galaxy experiences a phasetransition: from an essentially dead place, withpockets of low-complexity life restricted to planetarysurfaces, it will, on a very short timescale (essentiallyFermi’s colonization scale), become filled with high-complexity life. Consequences of such a scenario forSETI projects have been studied by Cirkovic (2004),where it has been shown that the difference in theoutcome of our estimates based on the Drake equa-tion can indeed be very different, depending on thedegree of gradualism assumed. All this lies firmlybeyond the scope of the adaptationist approach.

Modern comprehension of origin of life onEarth contributes to viability of Annis’ model. Fossilrecords indicate that unicellular, prokaryotic form oflife was originated more than once during early evo-lution of planet Earth and that their exterminationwas consequence of events in their astronomical envi-ronment (sudden and frequent collisions with mete-orites, radiation originated from near supernovae ex-plosion, gravitational perturbations, etc.). Complexform of life could evolve only when the frequency ofthat kind of events were reduced above some thresh-old. Nevertheless, mass extinction has played sig-nificant regulating role in development of life formsthat have led to intelligence. The most famous (andoften cited) example is sudden adaptive radiation ofmammals which after the dinosaur extinction, tooktheir place in empty ecological niches. Most spe-cialized forms of life suffered greatest damage whilemammals were much more primitive (vis-a-vis un-specialized teeth, nutriment, extremities, etc.) andthey simply have had more adaptive space to adjustto new environment conditions.

Astronomical events, such as supernovae ex-plosions could be source of high energy radiation thatcould have destroying effect on living beings. Al-though, radiation can cause hyperploidy, an increaseof DNA content in cells, and can induce DNA rear-rangements, so it is probable that evolution of life canbe affected by its radiation environment (e.g. Yanget al. 1994). Primary radiation damage does not di-

rectly lead to mutations, but requires modification,i.e. it has to be fixed so that it could be inherited.Big deletions are not the sole type of mutations thatdensely ionizing particles cause, but also point mu-tations that could be less lethal (Kiefer et al. 1994).

3.4. The problem of scales

In order to deploy the adaptationist solution,the relevant timescales for rise and devolution of tool-making intelligent species need to have particularrange of values. They, in turn, need to be accomo-dated within the know temporal framework of theGalactic chemical and dynamical evolution, as wellas the known stellar lifetimes. Although the detailedquantitative understanding of the age distribution ofthe potential life-bearing sites is still elusive, this isthe astrobiological field in which great strides havebeen made recently. And the results obtained so farindicate that the required concordance of timescalesmay not be so easy to achieve as it may seem.

The seminal work of Lineweaver and his col-laborators (Lineweaver 2001, Lineweaver et al. 2004)shows that the Earth-like planets began forming inthe Milky Way about 9.3 Gyr ago, while their aver-age age is 6.4 ± 0.9 Gyr. This is significantly largerthan the age of Earth (measured to be 4.56 ± 0.01Gyr; see Allegre et al 1995), indicating that the dif-ference between evolutionary ages of other biospheresin the Galaxy and ours should—on the Copernicanassumption of our average location and properties—be almost two billion years. This is exactly whatmakes Fermi’s paradox more serious than it was attimes of Fermi or even Hart-Tipler: considering rapidemergence of early life on Earth almost as soon asour planet became inhabitable (Oberbeck and Fogle-man 1989, Lineweaver and Davis 2002) the fact thatthe difference is so much larger than the Fermi’stimescale for crossing the Galaxy or creating astro-engineering projects detectable at huge distances isquite disturbing.

In principle, Fermi’s paradox in the original(or at least Hart’s [1975] form) can be written asthe relationship between timescales which should besatisfied at any life-bearing planet in the Milky Way:

tplanet + tbio + t↗ ≥ t0 (1)

where tplanet is the time of the planet formation (in

other words, the age of the Galaxy at the time of eachindividual planet formation); tbio is the timescaleof biological evolution (cf. Carter 1993) best un-derstood as the (mean) time required for reachingbiological complexity necessary for intelligence/tool-making; with t↗ we denote the rise of the advancedtechnological civilization, until its ”zenith” or, interms of the adaptationism, the timescale for flatten-ing of the fitness landscape; tFermi is the timescalefor large-scale Galactic colonization and/or creatingdetectable astroengineering markers; and t0 is thepresent epoch in the Galactic history (we can chooseto reckon it from the Galaxy formation, about 12

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Gyr ago). It should be kept in mind that all thesetimescales are indexed throughout the set of hab-itable planets (past and present). For the case ofEarth, tplanet is given by the value of about 4.5

Gyr, tbio is about 3.8 Gyr, and t↗ is at least about0.001 Gyr (i.e. since the appearance of the first in-telligent species of our hominid ancestors; the ex-act value is unimportant, as will be clearly seen).Finally, Fermi’s point was exactly that tFermi islikely to be of the order to magnitude of 0.01 Gyr,way smaller from either tplanet or t0. (In fact, a

non-trivial component of the paradox is the conjec-ture that for any location −→x in the Milky Way, thetimescale for reaching the vicinity of the Sun by mov-ing with average velocity 〈v〉, |−→x −−→x �| / 〈v〉, can beeffectively maximized by the timescale tFermi whichis orders of magnitude smaller than the present ageof the Galaxy.)

Now, the adaptationist solution can be refor-mulated as adding a term corresponding to the effec-tive timescale for the ”decline” of the species, i.e. re-version to the direct adaptation in the post-culturalstage:

tplanet + tbio + t↗ + tFermi ≥ t0 − t↘ (2)

where t↘ now stands for this reversion timescale.Obviously, it is easier to satisfy (2) than (1), whichwas the goal of the solution in the first place, but isit even formally sufficient? To see this, we can plugsome values from the distribution of the planetaryages, and consider some further simplifications. Forthe earlier planets, and neglecting Fermi’s timescale(since it is at least an order of magnitude smallerthan others), we obtain that all plausible values ofbiological and cultural timescales need to satisfy

tbio + t↗ + t↘ ≥ 3.7 Gyr, (3)

again, for any particular location in space.Potentially, the plausible values of the

timescales t↗ and t↘ could be established usingstochastic simulations constrained with some of themethodology currently used, for instance, to infer thespeed limits on evolution from the fossil record (e.g.Kirchner 2002). Unfortunately, at our present levelof ignorance, this is likely to give just a very broaddistribution of timescales; this remains an importantconstraint for any particular model of astrobiologicaldynamics.

3.5. Detectability or existence?

In a beautiful passage in Book V of his fa-mous poem De Rerum Natura, Roman poet and late-Epicurean philosopher Lucretius wrote the followingintriguing verses:

If there had been no origin-in-birthOf lands and sky, and they had ever beenThe everlasting, why, ere Theban warAnd obsequies of Troy, have other bardsNot also chanted other high affairs?Whither have sunk so oft so many deedsOf heroes? Why do those deeds live no more,Ingrafted in eternal monumentsOf glory? Verily, I guess, becauseThe Sun is new, and of a recent dateThe nature of our universe, and hadNot long ago its own exordium.6

Neglecting here its cosmological context of arguingfor a finite past age of the universe, this passage indi-cates an oft-neglected aspect of Fermi’s paradox—itis not enough to somehow remove all advanced tech-nological civilizations from our past light cone, butwe need to erase their more durable and potentiallydetectable achievements as well. The very existenceof the fascinating discipline of archaeology tells usthat cultures (and even individual memes) producerecords significantly more durable than themselves.It is only to be expected that such trend will con-tinue to hold even more forcefully for higher levels ofcomplexity and more advanced cultures. There areeven some factors related to the properties of our cos-mic environment that enhance this trend; notably, ithas already been repeatedly suggested that the tracesof any hypothetical extraterrestrial visitations in thepast of Earth and the Solar System would be easierto locate on the Moon than on Earth, due to thevastly supressed erosion there.

For further example, let us, for the sake of dis-cussion, allow that a significant fraction of advancedtechnological civilizations evolves toward the Karda-shev Type II (i.e. a community completely man-aging the energy output of its parent star); for theinformation-processing need of advanced communi-ties, see Cirkovic and Radujkov (2001). The straight-forward way of achieving this is the construction ofa Dyson shell (Dyson 1960). Once constructed, suchan example of astroengineering, will be quite durabledue to the properties of the interplanetary and in-terstellar space itself; like the Pyramids of Egypt, aDyson shell is likely to outlive its creators for a vastperiod of time, thus being an advanced analogue ofLucretius’ ”eternal monuments”. The preliminarysearches (e.g. Jugaku and Nishimura 2003) show theabsence of such artefacts in the Galactic vicinity ofthe Sun.

Those who wish to argue for adaptationismas the solution of Fermi’s paradox should make apause before discarding this complication. Even onthe adaptationist scenario, the duration of the tech-nological apex of a technological community can bevery long, likely expressed in millions of years. Thereis plenty of time to build not only Dyson shells,but perform many other durable and detectable as-troengineering feats. Their absence (to the best ofour current knowledge) testifies that the boundarybetween conscious tool-making and the state of di-

6In translation of William E. Leonard, available via WWW Project Gutenberg (Lucretius 1997).

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rect adaptation to environment is much sharper thanadaptationism would allow.

3.6. Contingency argument and adapta-tionism

The historical fact that some of distinguishedevolutionary biologists like George G. Simpson(1964) or Ernest Mayr (1993) have been scepti-cal about extraterrestrial life, intelligence and SETIprojects have been flaunted around every now andthen (e.g. Barrow and Tipler 1986, Tipler 1980).Neglecting extrascientific part of their arguments,7

this scepticism has ostensibly been based on the con-tingency argument: since the compartment of thebiological morphospace occupied by intelligent, tool-making beings is infinitesimally small, probabilitythat the evolutionary random walk will reach thatcompartment twice—even if the number of sites forevolution is measured in billions—is practically zero.While we cannot enter this very complex topic here,we notice that this is tightly related to the perceivedrole of contingency in terrestrial evolution, as high-lighted particularly vividly in the case study of theCambrian fauna od Burgess Shale (Gould 1989); ifwe ”rewind the tape” of evolution and let the BurgessShale fauna evolve again over the half a billion yearsthat had elapsed since the end of Cambrium, chancesthat human beings would appear are nil!8

It is a bit ironic that adherents to strict adap-tationism in terrestrial evolution, who were the tar-get of Gould’s persistent criticism not only in TheWonderful Life, but over the last three decades, andthose extending the strict adaptationism into realmsof sociobiology, behavioral ecology, or evolutionarypsychology, like Edward O. Wilson, Robert Wrightor William D. Hamilton, have argued that the evolu-tion of high intelligence was likely from the start(e.g. Wright 2000). A particularly forceful form ofsuch biological determinism has been recently putforward by the distinguished British paleontologistSimon Conway Morris (one of the heroes of TheWonderful Life!) in his book on Life’s Solution:Inevitable Humans in a Lonely Universe (ConwayMorris 2003). Conway Morris emphasizes the roleof convergence which increases the effective size ofthe morphospace compartment containing intelligentbeings. We do not need to take his claim as stronglyas the subtitle indicates: even if humans are not ”in-evitable”, some other form of intelligent life may aswell be, due exactly to the selective advantagesoffered, in short and medium term, by intelligenceand tool-making.

There is a clear message here, which tends tobe overheard, due to the often extrascientific noise(of which Conway Morris, with his worries aboutethics and the contemporary loss of values, is notinnocent). Those biologists wishing to uphold both

contingency argument and adaptationist solution toFermi’s paradox are operating a double standard:either a tool-making compartment is small every-where, convergence is unimportant, contingency all-important, and we are alone in the Galaxy (if notin the entire Hubble volume), or convergence sup-presses contingency at some level of complexity andselective advantages of tool-making are indeed more-or-less quickly found by Mother Nature; but notboth. To insist on both depending on the aspect ofthe problem (convergence dominant on Earth, butcontingency elsewhere) is a poor scientific attitudesmelling badly of anthropocentrism.9

4. DISCUSSION

We have hereby argued that adaptationist so-lution of Fermi’s paradox is insufficient in purely ex-planatory sense. Stressful physical and biotic envi-ronments resulting in adaptation and speciation arecrucial for evolution of life, especially high complex-ity forms of life with intelligence and consciousness.

Of course, one should keep in mind that inevolutionary biology term ”adaptation” is used inmore than one meaning. In contrast to adaptation,i.e. traits of specimens or populations, intelligencecould be appointed as ”adaptability”, i.e. the abil-ity of specimen and population to remain or be-come phenotypically (specimen) or genetically (pop-ulation) adaptive to variable conditions of environ-ment (Tucic 2003). According to that wider view,intelligence, and consciousness as her following phe-nomenon, could not be considered on a par with anyother trait of living beings.

Adaptationist solution to Fermi’s paradox is,in a sense, the counterpoint of the classical ”manda-tory self-destruction” solution, often repeated in theCold-War days by such SETI dissidents like von Ho-erner or Shklovskii (in his later writings). While self-destruction solution emphasized catastrophic frus-tration of being prevented by internal reasons of ful-filling the creative potential of our (and, by analogy,other) civilization, the adaptationist solution empha-sizes (in a gradualist manner) exactly the ultimatefutility of such fulfillment. We have tried to showhere that, however, in spite of its wider pretensions,adaptationism is as limited in astrobiology as is theCold War politics a form of relations in the humanhistory as a whole.

This conclusion is not entirely unexpected.Through dramatic increase of the very physical scopeof ecosystems considered, astrobiology offers strongincentive to explanatory pluralism. On the most ab-stract epistemological level, small systems are morelikely to have a satisfactory monist explanation thanthe large ones; to explain the topography of a village

7E.g. the worry about the magnitude of the U.S. federal debt in Mayr (1993).

8But see Dennett (1995) and Conway Morris (1998) for a critical assessment of the Burgess Shale argumentation.

9To add another ironic twist, Gould himself was one of the small number of evolutionists actively supporting SETI projectsthrough signing petition and public defense of its budget (Gould 1987).

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usually does not require any knowledge on the platetectonics. Similarly, even if the adaptationist ”shinyhappy consensus” is sufficient to account for the to-pography of the terrestrial design space, its chancesof being a universal explanatory strategy are reducedeven prior to any further inquiry into a particular as-trobiological problem.

Acknowledgements – Many helpful discussions withNick Bostrom, Fred C. Adams, Karl Schroeder, andZoran Zivkovic are deeply appreciated. Techni-cal help of Milan Bogosavljevic, Branislav Nikolic,Samir Salim, Dusan Indjic, Masan Bogdanovski,Sasa Nedeljkovic, and Vesna Milosevic-Zdjelar infinding several references is also acknowledged. Thisis an opportunity to thank KoBSON Consortium ofSerbian libraries, which enabled overcoming of thegap in obtaining the scientific literature during the

tragic 1990s in the Balkans. M. M. C. has been par-tially supported by the Ministry of Science and En-vironment of Serbia through the project no. 1468,”Structure, Kinematics and Dynamics of the MilkyWay.”

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ADAPTACIONIZAM NIJE REXEǋE FERMIJEVOG PARADOKSA

M. M. Cirkovic1, I. Dragicevic2 and T. Beric-Bjedov2

1Astronomical Observatory, Volgina 7, 11160 Belgrade 74, Serbia and Montenegro

2Faculty of Biology, University of Belgrade,Studentski trg 3, 11000 Belgrade, Serbia and Montenegro

Originalni nauqni radUDK 52–37

Jedan od najinteresantnijih problema umladoj oblasti astrobiologije jeste vixe odpola veka stari Fermijev paradoks: zaxto,kad uzmemo u obzir malu starost Zemǉe iSunqevog sistema u galaktiqkom kontekstu, nezapa�amo daleko starije inteligentne zajed-nice ili tragove ǌihove aktivnosti? Uprkossna�noj istra�ivaqkoj aktivnosti u posled-ǌim godinama, posebno podstaknutim uspesi-ma astrobiologije u pronala�eǌu ekstraso-larnih planeta i ekstremofila, ovaj prob-

lem (tako�e poznat kao problem ”Velike ti-xine” ili ”astrosocioloxki” paradoks) os-taje otvoren kao i uvek. U prethodnom qlanku,razmatrali smo jedno konkretno evolucionorexeǌe koje je predlo�io Karl Xreder nabazi danas dominantne evolucione doktrineadaptacionizma. Ovde mi proxirujemo tustudiju sa naglaskom na probleme sa kojimase takvo rexeǌe suoqava, i zakǉuqujemo da jeono u krajǌem ishodu malo verovatno.

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adaptationism fails to resolve fermi’s paradoxsaj.matf.bg.ac.rs/170/pdf/089-100.pdf ·...

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