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The selfish gene


召 な ″ ん ツ ツ ん 工 い 153 genes tO the new individual, and they alSO contribute equal amounts Of fOOd reserves. Sperms and eggs t00 contribute equal numbers Of genes, but eggs contribute far more in the way Of fOOd reserves: indeed sperms make no contribution at all, and are simply concerned with transporting their genes as fast as possible tO an egg. At the moment Of conception, therefore, the father has lnvested less than his fair share (). e. 50 per cent) Of resources ln the offspring. Since each sperm IS SO tiny, a male can afford tO make many millions 0f them every day. This means he is poten- tially able t0 beget a very large number of children in a very short period of time, using different females. This is only possible because each new embryo is endowed with adequate f00d by the mother in each case. This therefore places a limit on the number of children a female can have, but the number of children a male can have is virtually unlimited. Female exploitation begins here. Parker and others showed how this asymmetry might have evolved from an originally isogamous state 0f affairs. ln the days when all sex cells were interchangeable and of roughly the same size, there would have been some which just happened t0 be slightly bigger than others. ln some respects a big isogamete would have an advantage over an average—sized one, because it would get its embryo 0ff t0 a good start by givmg it a large initial 応 od supply. There might therefore have been an evolutionary trend towards larger gametes. But there was a catch. The evolu— t10n Of isogametes which were larger than was strictly necessary would have opened the door to selfish exploitation. lndividuals whO produced 〃 / ん r than average gametes could cash in, provided they could ensure that their small gametes fused with extra-big ones. This could be achieved by making the small ones more mobile, and able t0 seek out large ones actively. The advan- tage t0 an individual 0f producing small, rapidly movmg gametes would be that he could afford to make a larger number 0f gametes, and therefore could potentially have more children. Natural selection favoured the production Of sex cells which were small, and which actively sought out big ones t0 fuse with. SO we can think Of tWO divergent sexual 'strategles' evolving. There was the large-investment or 、 honest' strategy. This automatically opened the way for a small-investment exploitative or 、 sneaky' strategy. Once the divergence between the tWO strategies had

The selfish gene


ん ど ど 〃 ど 川 ac ん / 〃 ど 60 water-hole. Which is the best gambling strategy depends on all sorts 0f complex things, not least the hunting habit of the predators, which itself is evolved to be maximally efficient from their point 0f view. Some form of weighing up of the odds has to be done. But Of course we do not have to think of the animals as making the calculations consciously. All we have to believe is that those individuals whose genes build brains in such a way that they tend to gamble correctly are as a direct result more likely to survrve, and therefore tO propagate those same genes. We can carry the metaphor of gambling a little further. A gambler must think Of three maln quantities, stake, Odds, and prize. If the prize IS very large, a gambler is prepared to risk a big stake. A gambler who risks his all on a single throw stands to gain a great deal. He alSO stands tO lose a great deal, but on average high-stake gamblers are no better and no worse Off than other players wh0 play for 10W wmnings with low stakes. An analogous comparison is that between speculative and safe investors on the stock market. ln some ways the stock market is a better analogy than a caslno, because caslnos are deliberately rigged in the bank's favour (which means, strictly, that high-stake players will on average end up poorer than low-stake players; and low stake players poorer than those wh0 d0 not gamble at all. But this is for a reason not germane tO our discussion). lgnoring this, bOth high- stake play and low-stake play seem reasonable. Are there animal gamblers who play for high stakes, and others with a more con- servative game? ln Chapter 9 we shall see that it is often possible t0 picture males as high-stake high-risk gamblers, and females as safe investors, especially in polygamous specles in which males compete for females. NaturaIists wh0 read this book may be able to think of species which can be described as high-stake high-risk players, and Other specles which play a more conservative game. I now return tO the more general theme Of hOW genes make predic- tions' about the future. One way for genes to solve the problem of making predictions ln rather unpredictable envlronments IS tO build in a capacity for learning. Here the program may take the form of the following instructlons tO the survival machine: 'Here IS a list Of things defined as rewarding: sweet taste in the mouth, orgasm, mild temperature, smiling child. And here is a list 0f nasty things:

The selfish gene


example, the geneticist L. L. Cavalli-Sforza, the anthropologist F. T. Cloak, and the ethologist J. M. Cullen. AS an enthusiastic Darwiman, I have been dissatisfied with explanations which my fellow-enthusiasts have offered for human behaviour. They have tried to 100k for 'biological advantages' in vanous attributes Of human civilization. For instance, tribal religion has been seen as a mechanism for solidifying group iden— tity, valuable for a pack-hunting species whose individuals rely on cooperation t0 catch large and fast prey. Frequently the evolutionary preconception ln terms Of WhiCh such theories are framed is implicitly group-selectionist, but it is possible to re- phrase the theories in terms Of orthodox gene selection. Man may well have spent large portions of the last several million years living in small kin groups. Kin selection and selection in favour Of reclprocal altruism may have acted on human genes tO produce many 0f our basic psychological attributes and tendencies. These ideas are plausible as far as they go, but I find that they do not begin to square up t0 the formidable challenge of explaining culture, cultural evolution, and the immense differences between human cultures around the world, from the utter selfishness Of the lk of Uganda, as described by CoIin TurnbuII, to the gentle altruism 0f Margaret Mead's Arapesh. I think we have got to start again and go right back t0 first principles. The argument I shall advance, surprrslng as it may seem coming from the author of the earlier chapters, is that, for an understanding of the evolu- tion Of modern man, we must begin by throwing out the gene as the SOle basis Of our ideas on evolution. I am an enthusiast1C Darwinian, but I think l)arwinrsm is t00 big a theory tO be confined tO the narrow context Of the gene. The gene will enter my thesis as an analogy, nothing more. What, after all, is so special about genes? The answer is that they are replicators. The laws 0f physics are supposed t0 be true all over the accessible unlverse. Are there any prlnciples Of biology which are likely to have similar universal validity? When astronauts voyage t0 distant planets and 0k for life, they can expect tO find creatures t00 strange and unearthly for us tO imagine. But is there anything which must be true 0f all life, wherever it is found, and whatever the basis Of its chemistry? If forms Of life exist whose chemistry iS based on silicon rather than 205

The selfish gene


or thundery weather. 、 lore recently, laboratory simulations of the chemical conditions of earth before the coming life have yielded organic substances called 2 当 当 and rimidine These are building blocks of the genetic molecule, り 、 A ー . ltse に 一 Processes analogous to these must have grven rise to the prmeval soup' which biologists and chemists believe constituted the seas some three to four thousand million years ago. The organic substances became locally concentrated, perhaps in dry- lng scum round the shores, or in tiny suspended droplets. Under the further influence of energy such as ultraviolet light from the sun, they combined into larger molecules. Nowadays large organic molecules would not last long enough to be noticed: they would be quickly absorbed and broken down by bacteria or other living creatures. But bacterla and the rest Of us are late—comers, and in those days large orgamc molecules could drift unmolested through the thickening broth. At some point a particularly remarkable molecule was formed by accident. We will call it the ざ / な 町 . lt may not necessarily have been the biggest or the most complex molecule around, but it had the extraordinary property of being able to create copies of itself. This may seem a very unlikely sort of accident to happen. SO it was. lt was exceedingly improbable. ln the 、 lifetime of a man, things which are that improbable can be treated for prac- tical purposes as impossible. That is why you will never win a big prize on the football POOIS. But in our human estimates Of what is probable and what is not, we are not used to dealing in hundreds of millions of years. If you filled in P001S coupons every week for a hundred million years you would very likely win severaljack- potS. Actually a molecule which makes copies of itself is not as difficult to imagrne as it seems at first, and it only had to arise once. Think of the replicator as a mould or template. lmagine it as a large molecule consisting ()f a complex chain ()f various sorts of building block molecules. The small building blocks were abundantly available in the soup surrounding the replicator. Now SUPPOSe that each building block has an affinity for its own kind. Then whenever a building block from out in the soup lands up next tO a part Of the replicator for which it has an affinity, it will tend t0 stick there. The building blocks which attach themselves

The selfish gene


14 ど ゆ ″ 翩 知 ハ atoms are being formed in Stars all over the umverse, and were formed in the 'big bang' which, according to the prevailing theory, initiated the universe. This is originally where the elements on our world came from. Sometimes when atoms meet they link up together in chemical reactlon tO form molecules, which may be 1 ore or less stable. Such molecules can be very large. A crystal such as a diamond can be regarded as a single molecule, a proverbially stable one ln this case, but alSO a very simple one S1nce lts internal atomic structure is endlessly repeated. ln modern living organisms there are other large molecules which are highly complex, and their complexity shows itself on severallevels. The haemoglobin of our b 】 00d is a typical protein molecule. lt is built up from chains of smaller molecules, amlll() acids, each containing a few dozen atoms arranged in a precrse pattern. ln the haemoglobin molecule there are 574 amino acid molecules. These are arranged in four chains, which twist around each other to form a globular three- dimensional structure 0f bewildering complexity. A model of a haemoglobin molecule 100kS rather like a dense thornbush. But unlike a real thornbush it is not a haphazard approximate pattern but a definite invarlant structure, identically repeated, with not a twig nor a twist out Of place, over six thousand million million million times in an average human body. The precise thornbusw/ shape 0f a protein molecule such as haemoglobin is stable in the sense that tWO chains consisting Of the same sequences Of amino acids will tend, like two sprrngs, tO come to rest in exactly the same three—dimensional coiled pattern. Haemoglobin thornbushes are springing into their 'preferred' shape in your body at a rate of about four hundred million million per second, and others are being destroyed at the same rate. Haemoglobin is a modern molecule, used to illustrate the prin- ciple that atoms tend to fall into stable patterns. The point that is relevant here is that, before the coming of life on earth, some —rudimentary evolution of molecules could have occurred by ordinary processes Of physics and chemistry. There is no need to think of design or purpose or directedness. If a group of atoms rn the presence of energy falls into a stable pattern it will tend to stay that way. The earliest form Of natural selection was simply a selection Of stable forms and a rgection of unstable ones. There is

The selfish gene


18 7 ' ん ど が な 4 な Of human documents it is hard to think of examples where errors can be described as improvements. I suppose the scholars of the Septuagint could at least be said to have started something big when they mrstranslated the Hebrew word for 'young woman into the Greek word for 'virgin , commg up with the prophecy: 'BehoId a virgin shall concewe and bear a son. Anyway, as we shall see, erratic copyrng in biological replicators can ln a real sense glve r1Se tO improvement, and it was essential for the pro— gresslve evolution Of life that some errors were made. do not know how accurately the original replicator molecules made their copies. Their modern descendants, the DNA molecules, are astonishingly faithful compared with the most high-fidelity human copyrng process, but even they occasionally make mis- takes, and it is ultimately these mistakes which make evolution possible. Pr0bably the original replicators were far more erratic, but in any case we may be sure that mistakes were made, and these mistakes were cumulative. As mis-copyings were made and propagated, the primeval soup became filled by a population not of identical replicas, but of several varieties Of replicating molecules, all 'descended' from the same ancestor. Would some varreties have been more numerous than others? Almost certainly yes. Some varieties would have been inherently more stable than others. Certain molecules, once formed, would be less likely than others to break up again. These types would become relatively numerous in the soup, not only as a direct logical consequence of their 、 longevity', but also because they would have a long time available for making copies of them- selves. RepIicators of high longevity would therefore tend to become more numerous and, other things being equal, there would have been an 'evolutionary trend' towards greater longevity in the population of molecules. But other things were probably not equal, and another property Of a replicator variety which must have had even more importance ln spreading it through the population was speed of replication or 、 fecundity'. If replicator molecules of type 月 make copies Of themselves on average once a week while those Of type 召 make copies Of themselves once an hour, it is not difficult to see that pretty soon type 月 molecules are going to be far outnum- bered, even if they 'live' much longer than お molecules. There

The selfish gene


122 4 川 / ケ が 聞 〃 g ogamous species, the female may be wedded tO a male's territory rather than t0 him personally. If the population gets t00 big, some individuals will not get territories, and therefore will not breed. Winning a territory is therefore, tO Wynne-Edwards, like winning a ticket or licence to breed. Since there is a finite number of territones available, it is as if a finite number of breeding licences is issued. lndividuals may fight over who gets these licences, but the total number of babies that the population can have as a whole is limited by the number Of territones available. ln some cases, for instance ln red grouse, individuals dO, at first sight, seem to show restraint, because those whO cannot win territories not only do not breed; they also appear t0 give up the struggle t0 win a territory. lt is as though they all accepted the rules of the game: that if, by the end of the competi- tion season, you have not secured one Of the official tickets to breed, you voluntarily refrain from breeding and leave the lucky ones unmolested during the breeding season, so that they can get on with propagating the species. Wynne—F_,dwards interprets dominance hierarchies in a similar way. ln many groups of animals, especially in captivity, but also ln some cases in the wild, individuals learn each Other's identity, and they learn whom they can beat in a fight, and who usually beats them. As we saw in Chapter 5 , they tend to submit without a struggle t0 individuals who they 'know' are likely to beat them anyway. AS a result a naturalist is able tO describe a dominance hierarchy or peck order' ()o called because it was first described for hens)—a rank-ordering of society in which everybody knows his place, and does not get ideas above his station. Of course sometimes real earnest fights do take place, and sometimes individuals can promotion over their former lmmediate bosses. But as we saw in Chapter 5 , the overall effect of the automatic submission by lower-ranking individuals is that few prolonged fights actually take place, and serious imuries seldom occur. Many people think of this as a good thing' in some vaguely group-selectionist way. Wynne-Edwards has an altogether more daring interpretation. High-ranking individuals are more likely to breed than low-ranking individuals, either because they are preferred by females, or because they physically prevent 10W ー

The selfish gene


156 召 な ″ ん 研 励 ど seen. SuperficiaIIy, therefore, we might expect the daughter- producing gene tO go on spreading until the sex ratio was so unbalanced that the few remaining males, working flat out, could Just manage. But now, think what an enormous genetic advantage is enjoyed by those few parents who have sons. Anyone who lnvests in a son has a very good chance of being the grandparent of hundreds of seals. Those who are producing nothing but daughters are assured of a safe few grandchildren, but this is nothing compared to the glorious genetic possibilities which open up before anyone specializing in sons. Therefore genes for producing sons will tend tO become more numerous, and the pendulum will swing back. For simplicity I have talked in terms of a pendulum swing. ln practice the pendulum would never have been allowed to swmg that far in the direction of female domination, because the pres— sure tO have sons would have started tO push it back as soon as the sex ratio became unequal. The strategy of producing equal numbers Of sons and daughters IS an evolutionarily stable strategy, in the sense that any gene for departing from it makes a net loss. I have tOld the story in terms of numbers of sons versus num— bers of daughters. This is to make it simple, but strictly it should be worked out in terms Of parental investment, meaning all the 応 Od and Other resources which a parent has t0 offer, measured in the way discussed in the previous chapter. Parents should / 〃 0 ど equally in sons and daughters. This usually means they should have numerically as many sons as they have daughters. But there could be unequal sex ratios which were evolutionarily stable provided correspondingly unequal amounts Of resources were lnvested in sons and daughters. ln the case of the elephant seals, a policy 0f having three times as many daughters as sons, but of making each son a supermale by investing three times as much 応 od and other resources in him, could be stable. By investing more fOOd in a son and making him big and strong, a parent might increase hiS chances Of winning the supreme Of a harem. But this iS a special case. Normally the amount invested in each son will roughly equal the amount invested in each daugh- ter, and the sex rati(), in terms ()f numbers, IS usually one t() one. ln its long Journey down the generations therefore, an average

The selfish gene


On the other hand, if the choice IS not such a stark life or death choice, her best bet might be to prefer the younger one. For instance, suppose her dilemma is whether to give a particular morsel of 応 od to a little child or a big one. The big one is likely t0 be more capable 0f finding his own food unaided. Therefore if she stopped feeding him he would not necessarily die. On the other hand, the little one who is t00 young to find 応 od for himself would be more likely to die if his mother gave the food to his big brother. Now, even though the mother would prefer the little brother to die rather than the big brother, she may still give the food to the little one, because the big one is unlikely to die anyway. This is why mammal mothers wean their children, rather than going on feeding them indefinitely throughout their lives. There comes a time in the life of a child when it pays the mother tO divert investment from him into future children. When this moment comes, she will want to wean him. A mother who had some way of knowing that she had had her last child might be expected tO continue tO invest all her resources in him for the rest of her life, and perhaps suckle him well into adulthood. Never- theless, she should 'weigh up' whether it would not pay her more tO lnvest in grandchildren or nephews and nieces, srnce although these are half as closely related to her as her own children, their capacity tO benefit from her investment may be more than double that of one of her own children. This seems a good moment to mentlon the puzzling phenomenon known as the menopause, the rather abrupt termin— ation 0f a human female's reproductive fertility in middle age. ThiS may not have occurred t00 commonly in our wild ancestors, S1nce not many women would have lived that long anyway. But still, the difference between the abrupt change of life in women and the gradual fading out of fertility in men suggests that there IS something genetically 'deliberate' about the menopause—that it is an 'adaptation'. lt is rather difficult to explain. At first sight we might expect that a woman should go on having children until she dropped, even if advancmg years made it progressively less likely that any individual child would survive. Surely it would seem always worth trying? But we must remember that she is also related to her grandchildren, though half as closely. For varrous reasons, perhaps connected with the Medawar 135

The selfish gene


召 4 ″ ん 研 励 ど x for the particular arbitrary numbers which we started out with, but it is easy tO work out what the stable ratios would be for any Other arbitrary assumptions. As in Maynard Smith's analyses, we do not have to think of there being two different sorts Of male and two different sorts of female. The ESS could equally well be achieved if each male spends of his time being faithful and the rest 0f his time philan- dering; and each female spends 暑 of her time being coy and of her time being fast. Whichever way we think of the ESS, what it means is this. Any tendency for members Of either sex tO deviate from their appropriate stable ratio will be penalized by a con- sequent change in the ratiO Of strategies Of the Other sex, which is, ln turn, tO the disadvantage Of the original deviant. Therefore the ESS will be preserved. We can conclude that it is certainly possible for a population consisting largely 0f coy females and faithful males to evolve. ln these clrcumstances the domestic—bliss strategy for females really does seem tO work. We dO not have tO think in terms Of a consprracy 0f coy females. Coyness can actually pay a female's selfish genes. There are varlous ways in which females can put this type Of strategy into practice. I have already suggested that a female might refuse t0 copulate with a male who has not already built her a nest, or at least helped her to build a nest. lt is indeed the case that in many monogamous birds copulation does not take place until after the nest is built. The effect 0f this is that at the moment Of conception the male has invested a good deal more the child than just his cheap sperms. Demanding that a prospective mate should build a nest is one effective way for a female to trap him. lt might be thought that almost anything that costs the male a great deal would d0 in theory, even if that cost is not directly paid in the form 0f benefit to the unborn children. If all females of a population forced males to do some difficult and costly deed, like slaying a dragon or climbing a mountain, before they would consent tO copulate with them, they could in theory be reducing the temptation for the males tO desert after copulation. Any male tempted tO desert his mate and try t0 spread more 0f his genes by another female, would be put off by the thought that he would have to kill