spring books dimensions — the four dimensions of rela- zero) has always provoked the question of properties of replication, variation and tivistic space–time and six others of which whether spin is a property of particles or of competition is a “selfish replicator” that can we are unaware. Thus there is room for space. The materialization of particles from spread through populations by an analogue ample orthogonality to generate selection apparently empty space is similarly provok- of natural selection. Memes qualify as repli- rules that prevent bizarre happenings ing. String theory neatly answers them all. cators because bits of culture can be copied between particles. So what lies ahead? Not even Greene is by imitation and compete with other units The most persuasive part of Greene’s sure. String theory may not turn out to be for human attention. Thus, despite the dif- excellent book is that in which he persuades the cat’s whiskers he hopes. There are alter- ferences between memes and genes (genes, the reader that the problem of the six hidden natives, such as Roger Penrose’s twistor the- for example, are almost never passed to dimensions is not a problem but a matter of ory (which Greene reckons may say the same unrelated individuals), those memes most perspective. A garden hose seen from a great as strings). The most imaginative suggestion easily replicated and mimicked could prolif- distance looks like a one-dimensional object, in this imaginative book is that the time has erate, causing swift and important cultural but close up it is plainly a two-dimensional come to solve problems of quantum gravity change. Alarmed by the rampant and surface on which motion perpendicular to in strictly quantum language and not by uncritical adoption of this analogy by the length is perforce circular and repetitive. posing them in classical terms and then philosophers, psychologists and the popular The length of the hose is Greene’s analogy for ‘quantizing’ them. Meanwhile, there is a press, Dawkins downplayed the importance an ordinary extended dimension; the per- whole raft of algebraic geometry to be done. of memes in his later works. pendicular circular tracks stand for one of The thousand and more people working in However, in his foreword to Susan Black- the six wrapped-up dimensions. If the radius the field will need courage to do these largely more’s The Meme Machine, Dawkins notes of the circle (or of the garden hose) is small thankless chores, but this splendid book will that: “I was always open to the possibility enough, it is recognizable only in close-up cheer them on their way. that the meme might one day be developed (which means at the highest energy). Sir John Maddox is at 9 Pitt Street, London into a proper hypothesis of the human How small are the compact radii? It W8 4NX, UK. mind, and I did not know how ambitious seems to be agreed that the compact dimen- such a thesis might turn out to be.” The sions must be curled up with a radius in the thesis, called “memetics”, has now arrived, neighbourhood of the Planck length, which and it is indeed ambitious. Unfortunately, is the constant with the dimensions of The self-centred Blackmore’s book, aimed at both general length formed from Planck’s constant, New- readers and academics, proves to be a work ton’s gravitational constant and the velocity meme not of science, but of extreme advocacy. 3 of light. Formally, the length is £(hG/c ), The Meme Machine Teeming with untestable speculations, where h and G are the quantum and gravita- by Susan Blackmore indifferent to alternative theories and tional constants and c is the velocity of Oxford University Press: 1999. 258 pp. almost too grandiose to be taken seriously, light. Numerically, the length works out £18.99, $25 The Meme Machine offers a convoluted — 135 at 10 m, which is small enough for Jerry A. Coyne and wholly unsatisfying — explanation of Greene’s purposes. cultural and biological evolution. This is the kindergarten stuff of string The meme, defined as “any unit of cultural Blackmore defines memes as “units of theory, but Greene shrinks from no obstacle transmission or any unit of imitation”, was imitation”; her examples from humans in the path of understanding, instead turn- introduced by Richard Dawkins in the final include songs, fax machines, books, alcohol, ing each into an opportunity to make the chapter of The Selfish Gene. Dawkins’ mes- and any device, behaviour or idea that can be field exciting. The doctrine of supersymme- sage was that any entity with the gene-like copied. Memes can also be combined into try has become an intrinsic part of string ON T theory — otherwise ‘superstring’ theory. W The implication is that there are as many VID NE fundamental particles yet to be discovered A D as are now known, but all of them are much more massive. String theory will fall if it is ever shown that they do not exist. The essential step forward, and the cause of Greene’s rekindled enthusiasm, was taken by Witten in 1995. He showed that the five alternative string theories then defined are essentially equivalent. A weak coupling con- stant (or the strings’ equivalent of electric charge) in one will be the equivalent of another theory with a strong coupling con- stant. So, says Greene, the road points ahead to the age-old dream of predicting both the contents of the Universe and the properties of those contents. Already there are people working on the notion that black holes are merely very massive elementary particles. Even if the dream proves false, Greene has brought an absorbing field of enquiry to vivid life. The supposition that particles are not points but strings fits well with familiar phenomena. The fact that all particles of matter have intrinsic spin (which may be NATURE | VOL 398 | 29 APRIL 1999 | www.nature.com © 1999 Macmillan Magazines Ltd 767 spring books “co-adapted meme complexes” that include support the sociobiological theory that some memes spread and not others — is a stimulus for imitation (“good girls don’t humans (especially females) are attracted by completely neglected. Why did Christianity have sex before marriage”), and into even power and its attendant resources. take hold during the waning days of the larger “memeplexes”, such as religion, with Narrower hypotheses have additional Roman Empire? You won’t find the answer, many copy-able elements. Like Sherlock difficulties. A frequent problem is that the or any way to attain it, in memetics. (This, Holmes, Blackmore sees our brain as a room supposed meme seems to discourage its own by the way, makes memetics utterly unlike of limited size that can store only so many propagation. Such a case is Blackmore’s view biological evolution. The spread of genes memes. A meme’s success depends not on its that celibacy in Catholic priests is a meme through natural selection is not tautological benefits to the carrier, but on its ability to be that spreads by forcing clergy to divert their because one can predict their fate through replicated, retained and imitated. As she sexual energy into serving their religion. But their known effects on replication and the declares persistently: “If a meme can get what memes spring from this suppressed reproduction of their carriers.) itself successfully copied it will.” According sperm? If priests beseech their flocks to for- In a final effort to propagate her ideas, to Blackmore, this shibboleth explains ever refrain from reproduction, it is news to Blackmore constructs an extremely clever major aspects of our biology and culture, me. Other religions with non-celibate cler- coadapted meme complex: “Evolutionary including oversized brains, language, tech- ics, such as Islam, seem to have no trouble theory faced enormous opposition because nology, writing, contraception, adoption, attracting believers. it provided a view of humans that many altruism, vegetarianism, New Age ideas Finally, Blackmore sees consciousness as humans do not like. The same will probably such as alien abduction, and consciousness. a “selfplex”, an insidious band of memes that be true of memetics.” Well, call me Bishop Such an ambitious theory demands close conspire to give their carrier a false sense of Wilberforce, but in my view memetics is but scrutiny, but space restricts me to exploring self. Consciousness permits personal con- a flashy new wrapping around a parcel of old only a few of Blackmore’s views. She sug- viction, said to be especially good for and conventional ideas. gests, for example, that enlargement of the encouraging imitation (for example, “I love Jerry A. Coyne is in the Department of Ecology and human brain began when natural selection beer”). However, consciousness cannot be Evolution, The University of Chicago, 1101 East 57 improved the ability to imitate, followed by illusory: as the American philospher John Street, Chicago, Illinois 60637, USA. selection for ever more neurons to store suc- Searle has argued, thinking one is conscious cessful memes. Blackmore contends that is identical to being conscious. Moreover, such selection has occurred only in Blackmore’s scenario denies the possibility hominids and birds that learn songs. Subse- of consciousness to meme-less animals, and Shady secrets of the quently, memes further expanded our brain fails to explain the hardest problem of through sexual selection: as better imitators, human consciousness: subjective sensation. Enlightenment bigger-brained individuals are more attrac- How can memes account for the pain I feel Sex and the Gender Revolution, tive mates and leave more offspring. when I pinch myself? Volume 1: Heterosexuality and the One immediately smells trouble. First, But this is mere quibbling, for Black- Third Gender in Enlightenment there is no evidence that brain-size increase more’s enterprise has two fatal flaws.