Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.mso.anu.edu.au/~charley/papers/ConvergenceIntelligence10.pdf Дата изменения: Tue Nov 13 00:56:12 2007 Дата индексирования: Tue Oct 2 06:15:37 2012 Кодировка: Поисковые слова: http astrokuban.info astrokuban

To be published in From F ossils to Astrobiolog y Eds: J. Sec kbac h and M. Wals h, Springer 2008

PALEONTOLOGICA L TESTS: HUMAN- LIKE IN TELLIGENC E IS N OT A CONVERGEN T FEA TUR E OF EVOLU TION CHARLES H. LIN EWEA VER Planetary Science Institute, Research School of Astronomy and Astrophysics, Research Schoo l of Earth Scien ce, Austra lian Na tional University, Canberra, ACT 0200 Australia

1. The Planet of the A pes Hypothesis I taught a course called "Are We A lone?" at the Un iversity of New South W ales for a few years. The most popular lectur e was "The Great Drak e Equation Debate" ­ half a dozen "experts" would sit at the front of th e crowded lecture theater defend ing th eir estimates for the various terms in the Drake Equation ( an equation created by Frank Drake to estimate th e number of civilizations in the Milky Way with whom we might communicate via radio telescopes). Th e first terms of the equation ar e astronomical. How many stars are in our galaxy? -- most exper ts agreed -- about 300 billion. Wha t fraction of those stars are orbited by "Earth- like" p lanets? -- estimates ranged from ~100% to ~0.1 % dep ending roughly proportionally on ho w specific "Earth-like" was interpr eted to be. Th en came the more con ten tious bio logical terms: What fraction of these Earth-like plan ets would harbor life? I d efended a relatively high probability (~10%) based on how rapidly biog enesis occurred on Ear th ( Linew eav er & D avis 2002). We argued back and for th about how probable or improbable th e steps of mo lecular evolution wer e, that led to life on Earth -- and whether there were p laces on Ear th wher e lif e could still be emerg ing. We all learned a lot about bioch emistry, au tocataly tic cycles and hydrothermal ven ts. However , the most contentious ter m was: Once there is life of any kind, what is th e probability that it will evolve into a human-lik e in telligence th at can build and operate rad io telescopes? ( We defin e intelligence this way not ou t of some g eeky technophilic perversity but becau se posed this way, w e h ave the ability to answer the question by searching for other telescop es w ith our telescopes. So f ar, no signals from in telligent aliens h ave been iden tif ied , Tarter 20 01). In the "Great Dr ake Equ ation Debate" most of the invited experts assumed that once lif e got star ted it would get smar ter and smarter until one day, it would hit upon the idea of building a rad io telescope. Most students also subscr ibed to th is "stupid things g et smar ter" model of animal evolu tion and believed it to be a universal trend. I call this idea th e Plan et of th e Ap es Hypoth esis. The mov ie Plan et o f the Apes (1968) is set in the futur e af ter a catastrophic nuclear war between Homo sapiens. The surviving human s have lost th e ab ility to sp eak and have to forage in the w ild . Meanwhile, three species of apes (chimps, gorillas and orangutans) learn to speak English, rid e horses, farm corn, shoot rifles, and in gen eral begin to act like h airy Victor ian humano ids with human-like intellig ence. They mov e

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into th e recently emp tied "intelligen ce n iche" and turn in to the "functional equivalent of humans" (to use Carl Sagan's ter m, Sag an 1995a). On the Plan et of the Apes, humanlike in telligen ce is so ad aptive that it is a convergen t feature of evo lution -- species are waiting in the wings to move in and occupy the in telligence niche. G.G. Simpson in "The Nonprevalence of Hu manoids" (1964 ) articu lated th e case that humans (or any given species) were a quirky product of terrestrial evo lution and therefore w e should not expect to find humanoids elsewh ere. Thus stupid things do not, in gener al acquire human- lik e intellig ence. The ev idence we h ave tells us th at once extin ct, species do no t re-evo lve. Evolu tion is irreversible. This is known as Do llo' s Law (Do llo 1893, Gould 1970). Th e re- evolution of the same sp ecies is no t someth ing that happens only r arely . I t n ever has happen ed. Simpson also argued that b iologists, not physicists, can best judge th is issue because the problem is one of evolution ary systematics, not deterministic physics. Wheth er th ere is a trend in the fossil r ecord indicating that stupid things tend to g et smar ter, is an importan t and controversial issue in which the discussion has b ecome polarized into two camps. In one camp ar e the non-conver gentists (mostly b iologists) who, af ter studying the fossil r ecord, insist th at th e series o f even ts that led to humanlike intelligence is not a tr end, but a quirky resu lt of ev ents that w ill nev er repeat themselves eith er on Earth or anywher e else in the universe. In the oth er camp are th e convergentists (mostly physical scientists) who believe that stupid things get smarter and that intellig ence is a convergent f eature of evolution here and elsewh ere. See Linew eav er (2005) for more on the protagonists in th is d ebate. Is there any real ev idence for the Plan et of the Apes Hypothesis? Is human-like intellig ence a convergent featur e of evolution? Should we expect to find extraterrestr ials with human-like in telligen ce? D esp ite the lack of d irect eviden ce, we would like to assemble and evaluate the b est ind irect eviden ce for or against the idea that life (terrestrial or extr aterrestrial) evolv es towards human- lik e in telligence. The study of the evolutionary tr ends in the p aleonto logical record of lif e on Ear th is probably th e mos t relev ant evid ence and that is what is critically ex amined her e. 2. Frank D rake, Carl Sagan and Ernst Mayr In 1960 Frank Drake conducted the f irst r adio sear ch for extr aterrestrial intellig ence. H e is the Dir ector of the SETI (Search for Extra Terrestrial Intellig ence) Institu te's Center for the Study of Life in the Un iverse. SETI work would seem much more promising if there has been an evolu tion ary tr end among terrestrial lif e forms tow ards h igher intellig ence. On a f ligh t to a confer ence I asked him: "Frank, why do you think there ar e intellig ent aliens who have built radio telescopes? What d o you think is the strongest eviden ce for th e id ea that such human-like intellig ence is a convergen t feature o f evolution?" Fr ank's answ er w ent someth ing like th is: "The Earth 's fossil record is quite clear in showing that the complex ity of the centr al nervous system - par ticularly the cap abilities of the brain - has steadily increased in the course of evolu tion. Ev en the mass ex tin ctio ns did not set back this steady incr ease in brain size. It can be argued that extinction even ts

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expedite the developmen t of cognitive abilities, since th ose creatures with superior brains are better ab le to sav e themselves from th e sudden change in their environmen t. Thus smarter creatur es ar e selected, and the growth of intellig ence accelerates. We see th is effect in all varieties of animals -- it is not a fluke th at h as o ccurred in some small sub-set of an imal lif e. This pictur e suggests strongly that, g iven enough time, a b iota can ev olve not just one intellig ent species, bu t many. So co mplex lif e should occur abundantly." (Drake 2006) During the flight Fr ank referred me to th e debate b etw een biologist Ernst Mayr and planetologist Carl Sagan (Sagan 1995a,b, Mayr 1995a,b). Sagan ar ticulated the concept of "functionally equivalen t humans": "...when w e'r e talk ing about extraterr estr ial intellig ence, we ar e not talking-despite Star Tr ek--of humans or humanoids. We are talk ing about the functiona l equivalen t of humans-- say, any creatur es able to build and operate radio telescopes." (Sagan 1995a) "We are not requir ing that they follow th e particu lar route th at led to th e evolu tion of humans. There may be many differen t evolutionary path ways, each unlikely , but the sum of the number of pathways to intelligence may nevertheless be quite substan tial." ( Sag an 1995a) "...other th ings being equal, it is b etter to be smar t than to be stupid, and an overall tr end toward in telligen ce can be p erceived in the fossil r ecord. On som e worlds, the selection pressure for intelligence may be higher; on others, lower. " (Sagan 1995b) To which Mayr replied : "Sagan adopts th e principle "it is b etter to be smar t th an to be stupid ," but life o n Earth refu tes this claim. A mong all the forms of life, neith er the prokaryotes nor protists, fungi or plants h as evolved smartn ess, as it sho uld have if it wer e "better." In the 28 plus phyla of animals, in telligence evolved in only one (chordates) and doubtfully also in the cephalopods. And in the thousands o f subdivisions of the chordates, high intelligence developed in only one, th e primates, and even there only in one small subdiv ision. So much for the putativ e inevitab ility of th e dev elopment of high intellig ence becau se " it is better to be smar t."( Mayr 1995b) To which Sagan r e-replied : "Mayr argues th at prokaryotes and protista have not "evo lved smartness." Despite the great respect in which I hold Professor Mayr, I must demur: Prokaryotes an d protista ar e our ancestors. They hav e evolv ed smartness, along with most of th e rest of th e gorgeous d iversity of life on Ear th." (Sagan 1995b).

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Hold those poetic horses Carl! You're in Mayr's territory. By "prokaryotes and protists" Mayr is ref erring to ex tant organisms and their an cestors, after they d iverged from our lineag e. Th ese ancestors and their lineag es have continued to ex ist and evolv e and have not produced intellig ence. All together th at makes about 3 billion years of prokaryotic evo lution that did not produce high intelligence and about 600 million years of protist evolution th at did no t produce high intellig ence. 3. The Fossil Evidence for an Overa ll Trend Towards Intellig ence. The comments by Drak e (2006) and Sagan (1995b) abou t the fossil record showing eviden ce for a trend toward in creasing vertebrate en cephalization are ref erences primar ily to the work of paleoneurologist Harry Jerison ( Jerison 1973, 1975, 1991). Jerison has been measuring th e volume of modern and fossil animal skulls for sev eral decad es (Jer ison 1975). Jerison introduced the concep t of Encephalization Quotien t (E.Q.) , which is th e ratio of brain weight to some power (~2/3 or ~3/4) of the body weight. E.Q. is arguably th e most ob jective way to compare the in telligen ce of differ en t groups of encephalated an imals (J erison 1955, 1963, 1973). 4. Interpretation Problem # 1: Selection Bias: Choosing E.Q. because we hav e the highest E.Q. Every species has some uniqu e feature -- a feature th at makes it diff eren t from its closest liv ing relatives and from its ancestors. To make Fig. 1, Jerison first iden tif ied our unique featur e (high E.Q.) and then plo tted it as a f unction of time. Looking backward at the h istory of any existing extr eme tr ait w ill produce a similar app arent trend. The evo lutionary history of a featur e (iden tif ied as extreme today) is almost guaranteed to look something like Fig. 1. Therefore, we cannot consider th e trend seen in our lineage to b e a gen eral trend repr esen tativ e of any oth er lineages. If you choose a featur e becau se of its curren t extreme nature, it is no surprise that it had to get th at way and that its evo lution will display a tr end. But th is tr end has no claims to being represen tativ e of lif e in gen eral. Another examp le may mak e selection bias more obvious. Elephan ts have longer noses than their liv ing relativ es. Thus, wh en w e focus on this unique feature and p lot the sizes of the noses of its liv ing relativ es and of their evo lutionary ancestors (Fig. 2), w e find that in the series of progressively earlier an cestors, noses get progressively shorter . This is a selection effect that h as noth ing to do with a g eneral tenden cy that can be extrapolated to the rest of biology. Increasing nose size is not a gen eral feature of evolution. It is someth ing that occurred in the lin eag e th at led to elephants. After diverging from this lineage the N.Q . (nasalization quotient) of most groups stayed constan t.

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Figure 1. The Evolution of Relative Brain Size in G roups of Vertebrates Over the Past 200 Million Years (adapted and updated from Jerison 1976, p 96, Jerison 1991, Fig. 17). This plot seems to show an evolutionary trend towards increasing relative brain size ( = E.Q. = Encephalization Quotient) and is probably the most definitive evidence for such a trend. Average living mammal E.Q. is defined as 1. The broken lines indicate gaps in the fossil record. Variation within groups is not shown. The lineage that led to humans is drawn thicker than the other lineages.

Figure 2. The Evolution of Relative Nose Size (= N.Q. =Nasalization Quotient, ratio of nose length to body length) Over the Past 200 Million Years. Notice the apparent trend in the data as, over time, N.Q. reaches its ultimate value in extant pachyderms. Notice also that once the direct lineage that led to elephants is ignored, most of the species do not have an increasing N.Q. A few do (tapirs, aardvarks, proboscis monkeys) and such exceptions are discussed in "Interpretational Problem # 3". This preliminary plot is meant to illustrate a point, and should not be taken as more than a crude representation of a specious trend in N.Q. that has been largely ignored and poorly quantified by paleontologists. See Poulakakis et al 2002 and Benton et al 2005 for more detail.

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Figure 3. Same as Fig. 1 but we have removed the three lineages (dolphins, birds and ungulates/carnivores) with increasing E.Q. after diverging from our lineage. The lineage that leads to us provides no evidence of a generic trend towards increasing E.Q. because it has been selected to have that property. Notice that all of the increase in E.Q. is on the lineage that leads to humans. After diverging from us, all lineages shown here (lower vertebrates, archaic mammals, insectivores, prosimians, monkeys and apes) stayed at approximately the same E.Q. The lineages that remain flat represent the vast majority of all the species that evolved from the low E.Q. group shown in the lower left at 200 million years ago. The stasis of the E.Q. of the vast majority of species is evidence for an absence of selection pressure towards higher E.Q. The lineages whose E.Q. did increase after diverging from our lineage (dolphins, birds and ungulates/carnivores) are discussed in "Interpretational Problem # 3".

Another example: Humans hav e big brains with ex tremely small olf actory lobes. A similar analysis of the evolu tion of our olfactory lobe size would lead to the con clusion that the shrinkage of olf actory lob es is a gener ic tr end. Such a conclusion would b e misguid ed. By selecting an ex treme ou tly ing feature of an extant org anism (whether big or small, short or long, hard or sof t--anything as long as it is an outlier) th e evo lution of that feature in th at organ ism' s ancestors is very likely to show a monotonic tr end that leads up to th e outlier (Fig. 3). 5. Interpretationa l Problem # 2 Selection Bias: Non-Democratic Line Assignments In Fig. 1 some lines represen t one species (dolphin , humans) while o ther lin es repr esen t thousands of species ( archaic mammals) or tens of th ousands of species (low er invertebrates, see D awkins 2005). If our goal is to fairly r epresen t what has happened during evolution th en each lin e should r epresent an independent clad istic group: order, class or genus ­ someth ing demo cratic. However , hav ing some lines for single species and other lines for thousands of sp ecies is a biased non-representative form of gerrymandering. If one is look ing for a tr end, one n eeds to consider all the data, not just the data that support the tr end one wants to show. If the evolution of the E.Q .s of all

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species were plo tted, so me wou ld go up, some wou ld go down and the v ast major ity would stay the same. This variation is no t shown in Fig. 1 . 6. Interpretationa l Problem # 3: Non-independence of " convergence" on high E.Q. Consid er Fig. 1 again . After diverging from our lineag e, the incr easing E.Q . of birds, dolphins and ungulates/carnivores does seem to be evid ence for the trend in th e fossil record toward intelligence that Drake and Sag an were ref erring to. About three hundred and ten million years ago the last common ancestor of bir ds and humans had a small brain (E.Q . < 0.1). And 310 million years later birds and humans have bigger brains (E.Q. ~ 0.8 and E.Q. ~ 8 respectively) . About eigh ty five million years ago the last common an cestor of dolphins, humans and ungulates/carniv ores had a small brain (E.Q . ~ 0.2). And 85 million years later humans and dolphins hav e a b ig brain w ith E.Q . ~ 8 and ungulates/carnivores h ave an E.Q.~ 1. The E.Q. in all three lineages "indep endently" got bigger . Can we ex trapolate this indep endent convergence on high E.Q. to the evo lution of ex traterrestr ials? Simon Conway- Morris (2003, 2005) has documented man y cases of evolu tion ary convergence in evo lution: ­ bo th marsupial and p lacen tal mammals converged on sabertoothed carnivores (thylacosmilids and placental cats). The ability to fly evo lved in insects, pterosaurs (reptiles), b irds and bats (mammals). Conway- Morris and other authors have cited N indep endent examples of th e origin o f the ey e, wh ere N is some largish but indeter minate number . The co mmon an cestor of th ese "independen t" eye inventors did not hav e easily identifiable ey es, bu t it almost cer tainly d id have proto- eyes of some sort. The supposed independen ce of these converg ences is undermined by th e ~3.5 b illion years during which the cr eatures wer e biochemically and genetically id en tical, and during which they evolved their proto-eyes. They shared th e same genes, the same genetic machin ery of gene expression, regu lation, inhibition and activ ation that contro lled the g enetic exploration of morpho-space and the ability to tink er with the structure of the h ead and the placemen t and framing of photoreceptors. Many shared the same head and brain . The supposedly independ ent evolv ers of eyes, shar e the same basic bioch emistry and photorecep tor proteins and the same plasticity (West-Eb erhard 1989) that enabled an d constrained the morphological, preservable featur es that are sup erficially differ en t enough to be called "independen t". When consider ing convergen ce, a basic principle is of ten ignored: the extent of convergence cannot be larger than the extent of divergen ce from the common ancestor. With all terrestrial life having a common or igin, one must first qu antify th e degree o f divergence of two groups before one can discuss their convergence. For the species tha t converged on eyes, th is diverg ence could only take p lace during the relativ ely brief fraction of th eir existence as indep endent organisms. Roughly speaking, and depend ing on the eyes, the organisms w ere independen t for about 500 million years bu t shar ed a common an cestor for about 3500 million years. Thus they were ind ependent d ivergers for only ~10%-20% of their existen ce ( ~500 Myr / 4000 My r ~ 12%) and were identical for ~80%-90% of their existence. In other words, the common ancestor of the independen t ey es h ad, during ~ 3500 million y ears, alr eady evo lved the complex biochemical pathways for photorecep tion. In many detailed and fundamental

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biochemical and genetic w ays, th e purported "independ ent" originators (although they were phylogenetically isolated) were working in the same w orkshop, with the same tools and the same materials w ith the same set of genetic r egulator y skills. Similarly, th e co mmon an cestor of dolphins and human s who lived ~ 85 million years ago had a head , a small brain and ~ 500 million year common history of regulatory genes that tinkered w ith th e char acter istics of that brain. It had the same, (or very similar) bio chemical neural pathways and genetic p lasticity and constr ain ts that dolphins and humans are still endowed w ith . This 500 million y ear history produced a fin ite number of correlated non-independent w ays to adap t to en vironmental challenges. In other words, there wer e a finite number of highly evolved toggle switches that could be successfully tinker ed with. A mong th e two thousand sp ecies of Laurasiather es that diverged from our lineage 85 million y ears ago with the do lphins and carnivores/ungulates, all had heads and all h ad a similarly constrained potential for modification. There w ere thousands of species, undergoing a variety of environmental challeng es, and their ab ility to adapt to these challenges w as provided by hundreds o r thousands of shar ed toggle switch es. W e would expect some apparen t converg ences. What I am calling genetic "toggle switch es" is more ar ticulately and authoritativ ely describ ed as "conserved cor e processes", "facilitated variation" and "invisible anatomy" by Kirschner and Gerh art (2005). Similar arguments can be made about the increased nasalization quotients in tapir s, aardvarks and proboscis monkeys (Fig . 2). Th ey too converged on large noses. On ce noses wer e presen t and a common genetic tinkering apparatus had become availabl e from a long shared history, nose sizes in creased and decreased but mostly (like brains) just stayed the same size. Three and a half b illion years of iden tical evolu tion co mes with much bio logical baggage and many constr ain ts and it is these limited choices that are larg ely responsible for the apparent convergen ce on big brains. What Dr ake, Sagan and Conway- Morris have done is interpret correlated parallel moves in evolution as if th ey wer e unconstrained by shar ed evo lution bu t highly constr ain ed by a universal selection pressure towards in telligen ce th at cou ld be extrapo lated to ex traterrestrials. I am arguing just the opposite -- th at the apparen tly independ ent evolu tion toward higher E.Q . is largely constrained by shar ed evo lution with no evid ence f or some universal selection pressure towards intellig ence. If this view is correct, we cannot extrapo late the trends toward higher E.Q . to the evolution of extraterrestrials. If the convergence of dolphins and humans on high E.Q . has much to do with th e 3.5 Gyr o f shared history (and I argue that it has ev erything to do with it) then w e ar e not justif ied to extrapo late this convergence to oth er extr aterrestrial life forms that did not share this h istory. Extraterr estr ials ar e related to us in the sense that they may be carbon and water based ­ they may h ave poly mer ized th e same monomers using amino acids to mak e proteins, nucleo tid es to make a g enetic cod e, lip ids to make fats and sugars to make polysacchar ides. Howev er, our "common ancestor" w ith extraterrestrials was probably pre-biotic and did not share a common limited set of genetic togg le sw itches that is responsible for the apparen tly indep endent convergen ces among terrestrial life forms.

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Figure 4. Phylogenic tree of terrestrial life based on the 16s subunit of ribosomal RNA. The last common ancestor of all life is at the center of the tree ( labeled "Root"). The distance from the root to the end of each branch corresponds to the same amount of time ­ roughly 3.5 or 4.0 billion years. Because the ticking of the 16s molecular clock is not exactly uniform, the distances from the root to the ends of the branches are not the same length. Among the Eucarya in the lower left are the three twigs of complex multicellular life: Coprinus (representing fungi), Homo (humans, representing animals) and Zea ( corn, representing plants). The common ancestor of fungi, animals and plants lived ~1.5 billion years ago (Hedges et al 2004). Thus, the 200 million year time frame shown in Figs. 1 and 2 corresponds to the last ~2 mm of the twig labeled "Homo". Diagram from Lineweaver and Schwartzman (2004) based on Pace (1997). This RNA tree should be compared to Fig. 6.

We can use Fig . 4 to iden tify tr ends in the evolution of lif e, or convergences on some specific feature, wh ether it be E.Q., N.Q ., olfactory lobe size or eyeballs. First we randomly select a few of the ~60 branches shown. Then w e deter min e if two or mor e of them hav e independen tly evolv ed the feature of interest. For example, human- lik e intellig ence probab ly depends on th e existence of heads. Thus, we wan t to know if the tree of lif e shows any convergen ce towards heads. If heads were a convergent f eature of evolution one would expect independen t lineag es to evolve h eads. Our short twig on th e lower left lab eled "Homo " has heads, but h eads are found in no other branch. Our two closest relativ es, plants and fungi, do not seem to h ave an y tenden cy toward evolving heads. The evo lution of heads (encephalization) is ther efore not a convergen t feature of evolution. Heads are monophyletic and were once th e possessions of only one quirky unique species th at lived about six or sev en hundred million years ago. Its ancestors, no

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doubt possessed some kind of proto-head related to neural crests and placodes (Wad a 2001, Manzan ares and Nieto 2003). Drake (2006) stated that "[ intellig ence] is not a fluk e th at h as occurred in some small sub-set of animal life." However, Fig. 4 shows that in tellig ence, heads, even all animal lif e or multicellular life, may well be a fluk e that is a small sub-set of terr estr ial life. One poten tial problem w ith th is con clusion: I t is possib le th at existing h eads could hav e suppressed th e emergen ce of subsequent h eads. Such suppr ession wou ld be diff icu lt to establish. 7. Interpretationa l Problem #4: The Tenuous Link Betw een High E.Q. and Humanlike Intelligence About 600 million years ago, two kinds of metazo ans, protostomes and deuterostomes, diverged from each oth er. Both evo lved separ ately for ~600 million years and were very successful. Today there are about a million sp ecies of protostomes and about 600,000 species of deuterosto mes (of which we are one) . We consider ourselv es to be the smar test deu terostome. The most intelligent protostome is probably the octopus. Af ter 600 million years of independ ent evolu tion and desp ite their big brains, o ctopi do not seem to be on the v erge of build ing rad io telescopes. The d olphinoidea evolved a large E.Q. between ~60 million years ago and ~20 million year s ago ( Mar ino et al 2004). Thus, dolphins have had ~20 million years to build a radio telescope and have not done so. This strongly suggests that h igh E.Q. may b e a necessary, but is not a sufficien t condition for th e construction of rad io telescopes. Thus, ev en if th ere were a universal trend toward high E.Q ., th e link between high E.Q. and the ability to build a radio telescope is not clear. If you live underwater and have no hands, no matter how high your E.Q., you may not be able to build, or be interested in building, a rad io telescope. 8. A Universal Int ellig ence N iche? Life has been evolving on this planet for ~ 4 billion years. If the Plan et of the Apes Hypothesis is correct and th ere is an in telligen ce n ich e that w e hav e only recen tly occupied -- Who occupied it 2 billion years ago, or 1 billion years ago or 500 millio n years ago? Stromatilites? Alg ae? Jellyfish ? Sagan def ines "the functional equiv alent of humans" so nar rowly (creatures ab le to build and operate rad io telescopes) that on ly one species o n Ear th belongs to it ­ and then assu mes th at it is so broad that many aliens will fit in to it (Fig . 5). He is postulating an imagin ary group of species with only on e species in it. Most bio logists r efuse to take the id ea of such an imagin ary group seriously. In studying the variety of lif e on this planet, they see th at g eneral groups with only on e species in them are self-contr adictions that do not exist ­ probably no t a sound foundation upon which to build our hypotheses about ex traterr estr ial lif e.

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Figure 5 Consider the subsets of life in the Universe. We know that humans (black dot) are a subset of Life on Earth and we know that metazoans, fungi and plants are our closest relatives on Earth (small circle around the black dot). Sagan and others postulate an imaginary group of "functionally equivalent Humans" to which we (and some aliens) belong but none of our closest relatives do.

It seems unreasonab le to defin e in telligence so narrowly that only Homo sap iens h ave it on Earth ( among th e ~100 million sp ecies that h ave ever lived) and then imagine th at the human- lik e in telligence niche is so gener ic that ev en life forms very differ ent fro m ours (not shar ing 3.5 b illion y ears of evo lution) would evolv e in to it. Any given species that has evolv ed on the Earth w ill have its closest relativ es here on Earth . Thus, if we consider humans to be unique and alone on Earth, th en humans are a fortiori un ique and alone in the Univer se. We are more clo sely related to the life forms with whom we have shar ed 3.5 billion years of common an cestors than we w ill be with any alien evolved independen tly on anoth er plan et. Our closest relativ es, g enetically , physiologically and mentally are h ere on this Earth . 9. Conclusion The sear ch for ex traterr estr ial intellig ence is a sear ch for ourselv es. And therein lies its strength and w eakness. Knowing that we are search ing for o urselves giv es us th e strength and motivation to exp lore and find our p lace in the Universe. The weakness is the labyrin th of d ead-ends created by our n atural sense of self-importan ce and by our bias about what our place should be. Figure 6 is an older tr ee th an Fig. 4 and d isplays more obviously what w e w ant to b eliev e about ourselves.

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Figure 6. The Schwarzeneggerization of Life. A muscle-bound man stands as the end product of a linear progression--the Great Chain of Being ­a ladder of life that leads to male Caucasian weight lifters. One can create such an apparent linear trend out of the crooked phylogenetic branch of any species. Looking back from any particular species we will f ind the evolution of the traits of that particular species. However, precisely because we can construct such a figure from the lineage of any species, such a construction should not be construed as a general linear trend applicable to all life. The sim ple appeal of this figure is a good example of how easy it is to believe that the important events and the major transitions in evolution that led to us, are important events for all organisms (Smith and Szathmary 1995). The problems with this view ar e detailed in Gould (1989). The prevalence and recurrence of this mistaken interpretation of evolution needs to be avoided as we try to use terrestrial evolution to give us hints about the evolution of extraterrestrial life. Figure from Gatland and Dempster (1957). This homo-centric tree should be compared with Fig. 4.

If human-like intelligence w ere so usefu l, we should see many independen t examp les of it in biology, and w e could cite many cr eatures who had in volved on ind ependent contin ents to inhab it the "intelligence n iche". But we can't. Human-like intelligence seems to be what its name implies -- species specif ic.

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I have argued that the fossil record strongly suggests that hu man-like intelligence is not a convergen t featur e of evolution. Th e eviden ce is indir ect and suggestive, but it is, I think, the best w e h ave. D espite th is evid ence, I am a strong supporter of SETI -because I may be wrong about how the ev idence is b est in ter preted , and b ecause SETI is relatively ch eap science. SETI is th e exp loration of n ew par ameter space with new instruments ­ a proven recipe for scientific d iscov ery. However, w e do not need to misinterpret th e fossil record to justify this in spiring r esearch .

10. References
Benton, M. Cook, E. Hooker, J.J. (2005) Mesozoic and Tertiary Fossil Mammals and Birds of Great Britain, Geological Conservation Review Series, No. 32, Joint Na ture Conservation Committee, Peterborough, UK Conway Morris, S. (2003). Life's Solution: Inevitable Humans in a Lonely Universe, Cambridge University Press, Cambridge, UK Conway-Morris, S. (2005). Extraterrestrial Aliens like us? Astron. and Geophysics, 46, 4 Aug,. Dawkins, R. (2005). The Ancestor's Tale : A pilgrimage to the Dawn of Life, Weidenfeld and Nicolson Dollo, L. (1893) Les Lois de l'evolution Bull. Soc. belge Geol. Pal. Hydr., 7 164-166. Drake, F. (2006). On-line Debate Astrobiology Magazine, http://www.astro bio.net/news/article239.html Gatland, K.W. and Dempster, D.D. (1957). "The Inhabited Universe: an enquiry staged on the frontiers of knowledge" McKay, NY Gould, S.J. (1970). Dollo on Dollo's law: Irreversibility and the status of evolutionary laws, Journal of the History of Biology, Springer, Vol. 3, Number 2, September, 1970, 189-212 Gould, S.J. (1989). The iconography of an expectation. In W.W. Norton, Wonderful Life, , New York, pp. 23­ 52. Hedges, S.B. Blair , J.E., Venturi, M.L. and Shoe, J.L. (2004) A molecular timescale of eukaryote evolution and the rise of complex multicellular life, BMC Evolutionary Biology, 4,2 Jerison, H.J. (1955) Brain to body ratios and the evolution of intelligence. Science, 121: 447­449. Jerison, H.J. (1963) Interpreting the evolution of the brain. Hum. Biol. 35: 2 63-291 Jerison, Harry. (1973) Evolution of the Brain and Intelligence. New York: Academic Press Jerison, H.J. (1975) Fossil Evidence of the Evolution of the Human Brain. Ann. Rev. Anthropology, 4 27-58 Jerison, H.J, (1976).(see Fig. 17) - Paleoneurology and the Evolutionof Mind. Scientific American 234 (1): 90100 (plot on page 96) Jerison, H.J. (1991). Brain Size and the Evolution of Mind, American Museum of Natural History, New York. Kirschner, M.W. and Gerhart, J.C. (2005) The Plausibility of Life: resolving Darwin's dilemma Yale Univ. Press, 2005. Lineweaver, C.H. (2005). Book Review of Ulmschneider (2003) Intelligent Life in the Universe: From Common Origins to the Future of Humanity, Astrobiology 5,5,658-661 Lineweaver, C.H. and Davis, T.M. (2002), Does the Rapid Appearance of Life on Earth Suggest that Life is Common in the Universe? Astrobiology, Vol. 2, No. 3, 293-304 Lineweaver, C.H. and Schwartzman, D. (2004), Cosmic Thermobiology: Thermal Constraints on the Origin and Evolution of Life in the Universe, In: J. Seckbach (ed.) Origins: Genesis, Evolution and Diversity o f Life. Kluwer Academic, Dordrecht, pp. 233-248. , also available on-line at astro-ph/0305214 Manzanares, M. and Nieto, M.A. (2003) A Celebration of the New Head and an Evaluation of the New Mouth Neuron, Vol. 37, 895­898, March 27, 2003, Marino, L. McShea, D.W. Uhen, M.D. (2004) Origin and Evolution of Lar ge Brains in Toothed Whales TH E ANATOMI CAL RECOR D PA RT A 281A:1247­1255 Mayr, E. (1995a). Can SETI succeed? Not likely. Bioastron. News 7(3). Available online at: http://www.planetary.org/html/UPDA TES/seti/Contact/debate/Mayr.htm. Mayr, E. (1995b) The SETI debate Ernst Mayr reponds. http://www.planetary.org/html/UPDATES/seti/Contact/debate/Mayr2.htm Pace, N.R . (1997) A molecular view of microbial diversity and the biosphere. Science 276: 734-740. Poulakakis, N. Theodorou, G.E. Zouros, E, Mylonas, M. (2002), Molecular Phylogeny of the Extinct Pleistocene Dwarf Elephant Palaeoloxodon antiquus falconeri from Tilos Island, Dodekanisa, Greece, Mol. Evol 55: 364-374

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Sagan, C. (1995a) The Abundance of Life-Bearing Planets. Bioastron. News 7(4). Availab http://www.planetary.org/html/UPDA TES/seti/Contact/debate/Sagan.htm. Sagan, C. (1995b) Carl Sagan responds http://www.planetary.org/html/UPDATES/seti/Contact/debate/Sagan2.htm Simpson, G.G. (1964). The Nonprevalence of Humanoids. Science 143, 769-775. Smith, J .M and Szathmary, E. (1995). The Major Transitions in Evolution, WH Freeman, Oxford Tarter, J. (2001) The Search for Extraterrestrial Intelligence (SETI) Ann. Re v. Astron. Astrophys. Ulmschneider, P.(2003). Intelligent Life in the Universe: From common origins to the future Springer, Berlin Wada, H. (2001) Origin and evolution of the neural crest: A hypothetical reconstruction of its history Development, Growth and Differentiation 43 (5), 509­520 West-Eberhard, M.J. (1989) Phenotypic Plasticity and the Origin of Diversity, Ann. Rev. of Systematics, 20, 249-278

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