Chapter 7 Chapter 5 Aggressive Behavior: Stability and Selfish Machines

This chapter deals primarily with the largely misunderstood topic of aggressive behaviour.We shall continue to speak of the individual as a selfish machine programmed to do whatever is best for all of its genes as a whole.This way of speaking is for simplicity of description.At the end of this chapter we will return to the single gene. For a survival machine, another survival machine (not its own offspring, nor another close relative) is as much a part of its environment as a rock, a river, or a loaf of bread.This other survival machine can cause trouble, but it can also be exploited.One important difference between it and a rock or a river is that it tends to fight back.Because it is also a machine, with immortal genes on which its future rests, and in order to preserve these genes, it will go through fire and water.Natural selection favors genes that control their survival machines to make the most of their environment, including other survival machines of the same species and of different species.

At times, survival machines seem to have little effect on each other's lives.Moles and blackbirds, for example, do not eat each other, mate, or compete for territory.Even so, we can't think that they have nothing to do with each other.They may be competing for something, perhaps for earthworms.That doesn't mean you'll see moles and blackbirds vying for an earthworm; in fact, a blackbird may never see a mole in its life.But if you wiped out the mole population, there might be a noticeable effect on the blackbird, though I dare not speculate about the details of the effect, or by what indirect route of tortuous encounters.

Survival machines of different species interact with each other in a variety of ways.They may be predators or prey, parasites or hosts, or rivals for some rare resource.They can be exploited in various special ways, for example, flowers use bees as pollinators. Survival machines belonging to the same species tend to affect each other's lives more directly.This happens for many reasons.One reason is that half the members of one's own species are likely to be potential mates, and industrious and useful parents to their offspring; Both are machines that preserve genes in the same kind of place, and have the same way of life, so they are more direct competitors for all the resources necessary for life.The mole may be a rival to the blackbird, but it is not nearly as important as the other blackbird.Moles and blackbirds may compete for earthworms, but blackbirds and blackbirds compete with each other not only for earthworms but for everything else.They may also compete for mates if they are of the same sex.Usually male animals compete with each other for female mates, for reasons we shall see.This suggests that a male may be doing his own genes a favor if he does harm to another male he is competing with.

Thus, the logical strategy for a survival machine seems to be to kill its competitors and then, preferably, eat them.Although slaughter and cannibalism do occur in nature, to think that it is common is a naive understanding of the theory of the selfish gene.In fact, Lorenz emphasized the restrained and gentlemanly nature of animal fights in his book On Aggression.In his opinion, one thing to note about animal fights is that they are a normal competitive activity, played according to rules like boxing or fencing.Animal combat is a fight fought with a blunt sword or with gloves on.Threats and bravado have replaced real threats and bravado.The victor respects the gesture of submission, which does not mortally blow or bite the surrender, as our naive theories may assert.

Interpreting animal aggression as restrained and regulated behavior can be controversial.Especially to say that poor historic humans are the only species to slaughter their own kind, the sole heirs of the mark of cain and all the lurid accusations of the like.Whether a naturalist emphasizes the violent or restrained side of animal aggression depends partly on the kinds of animals he usually observes, and partly on his biases in evolution. Lorenz is, after all, an advocate of the interests of the species. people.Even if descriptions of how animals fight are somewhat exaggerated, there is at least some truth to the idea that animal civilizations fight.On the surface, this phenomenon appears to be a form of altruism.The theory of the selfish gene has to take on the difficult task of explaining this phenomenon.Why don't animals go out of their way to kill rivals of their own species at every possible opportunity?

The general answer to this question is that there are benefits as well as costs to that kind of doom and gloom, and not just the obvious loss of time and energy.For example, suppose both B and C are my competitors, and I happen to meet B.As a selfish individual, I should try to kill B.But take it easy and listen to me. C is both my opponent and B's opponent.If I kill B, I get rid of an opponent for C, and I do a good thing for C invisibly.It may be better if I let B live, because then B may compete or fight with C, and I can reap the benefits.There is no apparent benefit to killing an opponent indiscriminately, and that is the moral of this hypothetical simple example.In a large and complex competitive system, getting rid of a competitor is not necessarily a good thing, and other competitors are likely to get more benefits from it than you.Those officials responsible for controlling pests were taught such harsh lessons.You have a serious agricultural pest, you discover a good way to get rid of it, and you happily do it.Little do they know that the eradication of this kind of pest benefits another kind of pest, and its degree even exceeds the benefits to human agriculture.As a result, your situation is worse than before.

On the other hand, it seems like a good idea to discriminately kill, or at least wrestle, certain specific competitors.If B is an elephant seal with a large harem, and I am an elephant seal, and I can get his harem by killing him, then I might be wise to do so .But even in selective wrestling there are losses and risks.It is in B's interest to fight back to defend his valuable property.Had I provoked a fight, I would have ended as it had, probably in death.Maybe it is even more likely that I will die and it will not die.I want to wrestle it because it holds a valuable resource.But why does it have such resources?It may have been won in battle.It may have beaten off other challengers before it fought me.It could be a valiant fighter.Even if I win the fight and get the wives, I may be seriously injured in the fight and not be able to enjoy the benefits.Also, wrestling drains time and energy.It may be better to temporarily save time and energy.If I focus on eating and not messing around for a while, I grow bigger and stronger.Eventually I'll fight it for the wives, but I may have a better chance of winning if I wait a bit instead of rushing in now.

The above self-monologue is purely for illustration: before deciding whether to fight or not, it is best to make a complex, if unconscious, but complex weighing of gains and losses.While there are undoubtedly certain advantages to be gained from wrestling, it is not all advantages and disadvantages.Likewise, during the course of a fight, every tactical decision involving escalation or de-escalation has its pros and cons, and these pros and cons can in principle be analysed.Individual ecologists have known this for a long time, albeit not quite clearly, but only Smith, who is not usually considered an ecologist, has made it so forcefully and clearly .He collaborated with G.R. Price and G.A. Parker on a branch of mathematics called Game Theory.Their original insights can be expressed in words rather than mathematical symbols, though with some loss of precision.

The evolutionarily stable strategy (hereinafter referred to as ESS) is the basic concept proposed by Smith.He traced back to the source and found that the first to have this idea was Hamilton (W.D.Hamilton) and MacArthur (R.H.MacArthur).A policy is a pre-programmed policy of behavior.For example, attacking an opponent; chasing if it flees; fleeing if it fights back is one strategy.It is important to understand that the strategies we are talking about are not consciously formulated by the individual.Don't forget that we're picturing animals as robotic-like survival machines whose muscles are controlled by a preprogrammed computer.Writing a strategy into a simple set of instructions in words is just for our convenience.Animal behavior, produced by some mechanism that is difficult to specify, seems to be based on such instructions.

Most members of the population adopt a certain strategy, and the benefits of this strategy are not comparable to other strategies, this strategy is evolutionarily stable strategy or ESS.The concept is both subtle and important.In other words, the best strategy for an individual depends on what most members of the population are doing.Since the rest of the population is also made up of individuals all trying to maximize their respective achievements, what will persist will be a strategy that, once established, cannot be compared with the strategy of any individual behaving abnormally. Among them.After a major change in the environment, there may be a short period of evolutionary instability in the population, and there may even be fluctuations.But once an ESS is established, it becomes stable: deviations from the ESS will be punished by natural selection.

To apply this idea to explaining aggression, let's consider one of the simplest examples that Smith postulates.Suppose there is a particular species called eagle and dove. There are only two fighting strategies in the population.In our hypothetical population, all individuals are either hawks or doves.The hawk always fights with all his might, desperately, and never backs down unless he is seriously wounded; but the dove only threatens and intimidates in the customary and graceful manner, never harming other animals.If the hawk fights the dove, the dove runs away quickly, so the dove is not hurt.If hawks fight hawks, they will fight until one of them is seriously injured or dies.If pigeon meets dove, no one is hurt; they engage in a confrontation for a long time, until one of them gets tired, or gets bored and decides not to continue the confrontation, and thus makes a concession. .Let us assume for the moment that an individual cannot know in advance whether its opponent is a hawk or a dove.It only knows when it's wrestling with it, and it can't remember which individuals it has wrestled with in the past, so it can't learn from it. Now, as a purely arbitrary rule of the game, we stipulate the following scoring criteria for competitors: fifty points for a win, one point for a loss, one hundred points for a serious injury, and ten points for a protracted and wasted game.We can think of these scores as a currency that translates directly into genetic survival.Individuals with high scores and high average profitability will leave many genes in the gene pool.On a broad scale, the actual numbers don't mean much for analysis, but they help us think about it. It is not of interest to us whether the hawk has a tendency to beat the dove when the hawk fights the dove, which is important.We already know the answer to that question: Eagles always win.What we want to know is whether the hawk or the dove is the evolutionarily stable strategic type.If one of them is an ESS type and the other is not, then we think that the ESS type will evolve.Theoretically, it is possible that there are two ESS types.No matter what strategy happens to be adopted by the majority of members of the population (whether the hawk strategy or the dove strategy) for any individual, if the best strategy is to follow the crowd, then two ESS types are possible .In this case, the population generally remains in the one of its two stable states which it reaches first.However, as we shall see, both of these strategies, hawk or dove, are in fact unlikely to be evolutionarily stable on their own, so we should not expect either of them to evolve.To illustrate this, we have to calculate the average profit. Suppose there is a population consisting entirely of pigeons.No matter when they fight, no one is hurt.Such contests are long, ritualized contests, perhaps eye-to-eye confrontations, which end only when one opponent backs down.The victor then gets fifty points for gaining the resource in question, but is penalized for wasting time by staring at each other for a long time - ten points, so a net forty points.And the loser was penalized - ten points for wasting time.On average, each pigeon can be expected to win and lose 50/50.The average profit per game is therefore the average of +40 points and -10 points, which is +15 points.So, every pigeon in the pigeon population seems to be doing well. But now suppose a mutant eagle appears in the population.Since he was the only hawk around, every fight he fought was with the dove.The hawk is always unbeaten against the dove, so he nets +50 points per fight, and this number is his average profit.Since the dove's profit is only +15 cents, the hawk enjoys a huge advantage.As a result, hawk genes spread rapidly through the population.But the hawk can no longer count on the doves for all its opponents.To take another extreme example, if the successful spread of the hawk gene causes the entire population to become dominated by hawks, then all fights become hawk-to-hawk fights.This time the situation is completely different.When hawk meets hawk and one of them is badly wounded, he gets -100 points, while the victor gets +50 points.Each hawk in a hawk population is expected to win a fight half and half.Its average expected profit per fight is therefore +50 cents and -100 cents in half, or ︱ twenty-five cents.Now let's imagine a solitary dove living in a population of hawks.There is no doubt that it loses every fight.But on the other hand it never hurts.Therefore, its average payoff in the hawk population is , while the average payoff for hawks in the hawk population is -25 cents.Pigeon genes therefore have a tendency to spread out in the population. According to the way I describe it, it seems that there is a continuous swing state in the population.The hawk genes skyrocket to rapid dominance; the result of the hawk majority is that the dove genes necessarily benefit, and the numbers increase until the hawk genes start multiplying again, and so on.It doesn't have to be that volatile, however.There is a steady ratio of hawks to doves.You just do the math on whatever prescribed scoring system we use, and the result is a steady ratio of doves to hawks of five/twelve:seven/twelve.Up to this steady ratio, the average payoff of hawks and doves is exactly the same.Therefore, natural selection does not favor A over B, but treats them equally.If the number of hawks in the population starts to rise, the ratio is no longer seven/twelve, and the doves start to gain an extra advantage, and the ratio returns to a steady state again.As we shall see the stable ratio of sexes is fifty:fifty, so in this hypothetical example the stable ratio of hawks to doves is seven:five.In both of the above ratios, if a swing from the stable point occurs, it need not be very large. This situation sounds a bit like group selection at first glance, but it actually has nothing in common with group selection.The reason this sounds like group selection is that it reminds us of a population in a stable equilibrium that tends to gradually recover whenever that balance is upset.But ESS is a far more subtle concept than group selection.It has nothing to do with the fact that some groups are more successful than others.This is well illustrated by applying the arbitrary scoring system in our hypothetical example.In a stable population consisting of seven/twelve hawks and five/twelve doves, the average payoff for an individual turns out to be sixty-one/four points.This is true whether the individual is a hawk or a dove.Sixty-one/four points is much less than the average profit per pigeon in a population of pigeons (fifteen points).As long as everyone agrees to be a pigeon, each individual benefits.According to pure group selection, any group whose individuals all agree to be doves will achieve much more than a competing group that stays at the ESS ratio. (Actually, a group consisting purely of pigeons is not necessarily the most successful group. In a group consisting of 1/6 hawks and 5/6 doves, the average profit per game is 162 /Three points. The group formed according to this ratio is the most likely to succeed. But as far as the current topic is concerned, we don’t need to consider this situation. For each individual, it is relatively simple to form a group composed entirely of pigeons , since the average profit of each individual is 15 cents, it is much superior to ESS.) Therefore, group selection theory believes that the evolution to a group composed entirely of pigeons is a development trend, because eagles account for 7/12 groups Less likely to succeed.The problem is that even those groups that offer benefits to each of its members in the long run are bound to have bad apples.It is true that every single pigeon in an all-pigeon colony is better off than a pigeon in an ESS colony.Unfortunately, in the group of pigeons, a single-handed hawk can do unparalleled deeds, and no force can stop the evolution of hawks.Therefore, the group could not escape the doom of disintegration due to internal betrayal. The stability of the ESS population is not because it is particularly beneficial to the individuals in it, but only because it has no hidden danger of internal betrayal. Human beings are able to form various alliances or groups, even if these alliances or groups are not stable in the sense of ESS, they are beneficial to each individual.This situation is possible only because each individual can consciously use his foresight ability, so that he understands that it is in his own long-term interest to abide by the provisions of the covenant.The temptation for some individuals to violate the covenant for the possibility of large short-term benefits can become overwhelming.This danger is always present even in the covenants made by human beings.Monopoly prices are perhaps the most telling example.It is in the long-term interest of all gas station owners to set the flat price of gasoline at some artificially high level.Those price-manipulating groups can exist for a considerable period of time because they make conscious estimates and judgments about the highest long-term interests.But every now and then an individual is tempted to lower the price by the temptation to make a quick profit.The peers near this kind of person will immediately follow suit, and the wave of lower prices will spread to the whole country.To our regret, the conscious foresight of the gas-station owners now resumes its role and concludes a new pact to monopolize prices.So, even in a species endowed with the gift of conscious foresight, human beings, pacts or groups based on the highest long-term interests are often on the verge of falling apart due to internal rebellion.Even less often, group interests or group strategies can develop in wild animals, where they are controlled by competing genes.What we can see must be: Evolutionarily stable strategies are everywhere. In the above example, we simply assumed that each individual was either a hawk or a dove.We end up with an evolutionarily stable ratio of hawks to doves.In fact, that is to say that the genes for the hawk and the genes for the dove achieve a stable ratio in the gene pool.This phenomenon is called stable polymorphism (polymorphism) in the terminology of genetics. As far as mathematics is concerned, a completely equal ESS without polymorphism can be achieved through the following approach.If each individual can behave either as a hawk or as a dove in each particular competition, an ESS can be achieved in which all individuals have exactly equal probability of behaving like a hawk.In our concrete example the probability is seven/twelve.In fact, this situation shows that each individual, participating in each competition, has decided arbitrarily in advance whether to act like a hawk or a dove in this competition; although the decision is made at will, it is always taken into account. To the ratio of hawks to seven doves to five.While these decisions are in favor of the hawks, they must be arbitrary, in the sense that it is crucial that an opponent cannot guess in advance what the other will do in any particular contest.For example, it is absolutely not advisable to play the role of the hawk for seven fights in a row, then the dove for five fights in a row, and so on.If any individual employs such a simple fight sequence, its opponents will quickly see through the tactic and take advantage of it.Against this strategist who uses simple fight sequences, you are only in a good position to fight with hawk moves knowing that he is acting as a dove in the fight. Of course, the story of the hawk and the dove is a bit childishly simple.It's a pattern that, while it doesn't actually happen in nature, can help us understand what's actually happening in nature.Patterns can be very simple, as in our hypothetical pattern, and still be useful for understanding an argument or developing a concept.Simple patterns can be enriched and extended to gradually form more complex patterns.If all goes well, as the patterns become more complex, they will become more like the real world.One way to develop the hawk-dove model is to introduce more strategies.Hawks and doves are not the only possibilities.A more complex strategy introduced by Smith and Price is called the Retaliator. The retaliator behaves like a dove at the beginning of each fight, that is to say, it is not like a hawk, which is desperate and ferocious at the beginning of the attack, but puts on the usual threatening confrontation posture, but once the opponent attacks it, It fights back.In other words, a retaliator behaves like a hawk when attacked by a hawk, behaves like a dove when confronted by a dove, and behaves like a dove when confronted by another retaliator .A riposte strategist is a conditional strategist.Its behavior depends on the behavior of the other party. Another conditional strategist is called a bully.It behaves like a hawk in every way, but when it is struck back it flies away.Another kind of conditional strategist is the prober-retaliator.It's basically like a riposte strategist, but also tentatively sometimes escalates the contest briefly.If the opponent does not fight back, it persists in acting like a hawk; on the other hand, if the opponent fights back, it reverts to the usual threatening posture of the dove.If attacked, it returns fire just like a normal riposte tactician. If all five of the strategies I mentioned were pitted against each other in a computer simulation, only one of them, the riposte strategy, was evolutionarily stable.Tentative retaliatory tactics are nearly stable.The dove strategy is unstable because hawks and bullies invade the dove population.The hawk strategy is also unstable since the hawk population is subject to attack by doves and bullies.The bully strategy is also unstable due to the fact that the bully population is subject to encroachment by hawks.In a population of retaliators, since no other strategy does better than retaliator itself, it will not be violated by any other strategy.However, the pigeon strategy can also perform equally well in a population composed of pure retaliators.This means that, other things being equal, the number of pigeons will slowly and gradually rise.If the number of doves rises to a considerable extent, the tentative retaliator strategy (and along with the hawk and the bully) starts to gain the upper hand, because they perform better against the dove than the retaliator strategy.The tentative-retaliator strategy itself, unlike the hawk and the bully strategies, performed better, and only slightly, in the population of tentative-retaliator strategies, the riposte strategy, than it.In that sense, it's almost an ESS.We can therefore imagine that a mixture of riposte and tentative riposte might tend to predominate, perhaps even with a modest swing between the two strategies, and at the same time the very small proportion of pigeons increase in number reduce.We no longer have to think about problems based on polymorphism, because according to polymorphism, each individual will never adopt this strategy, or adopt another strategy.Each individual can in fact employ a complex mix of riposte, heuristic riposte, and pigeon strategy. The conclusions of this theory are not far from the actual situation of most wild animals.In a sense, we have addressed the civilized side of animal aggression.As for the details, of course it depends on the actual score of wins, injuries and wasted time etc.For the elephant seal, the winning prize may have been the near exclusive right to a large group of wives.Therefore, the profit of this kind of winning should be said to be very high.It's no wonder that fighting is so vicious and the possibility of serious injury is so high.Compared with the cost of being injured in a fight and the benefits of winning, the cost of wasting time should be said to be small.But on the other hand, for a small bird in a cold climate, the cost of wasting time can be enormous.Great tits feeding chicks need to catch an average of one prey every thirty seconds.Every second of the day is precious.In hawk-to-hawk combat, the time wasted is relatively brief, but perhaps it should be considered a more serious matter than the risk of injury to them.Unfortunately, we know too little about the losses and benefits of various activities in nature to come up with actual figures.We cannot easily draw conclusions purely from our own arbitrarily chosen numbers. These general conclusions are important that ESSs tend to evolve; that ESSs are not the same as the best that can be achieved by any group group; and that common sense can lead people astray. Another type of war game that Smith contemplates is called a war of attrition.It may be thought that this war of attrition takes place in a species which never engages in dangerous combat, perhaps a well-armoured species, which is less likely to be injured.All disputes among this species are settled by posturing in the traditional manner.Contests always end with concessions by the party participating in the contest.If you want to win, all you have to do is keep your eyes on the opponent and hold on until the opponent finally runs away.It is obvious that no animal can be threatened indefinitely; for there are important things to do elsewhere.The resources it competes for are valuable, but not infinite in value.It was worth only so much time, and as at auction, everyone was prepared to pay only so much.Time is the currency used in this auction with only two bidders. We assume that all of these individuals estimate precisely in advance how long a particular resource (such as female animals) is worth spending.Then a mutant individual who intends to give it a little more time is always the winner.Therefore, a strategy with a fixed bid limit is unstable.Even if the value of the resource can be estimated with great precision and all individuals bid appropriately, this strategy is unstable.If any two individuals bid according to the limit strategy, they will stop bidding at the same instant, and no one will get this resource as a result!In this case, it is better to simply abstain from the beginning than to waste time in the competition.The important difference between a war of attrition and an actual auction is that in a war of attrition, after all, both parties in the contest pay the price, but only one gets the item.Therefore, in a population of extreme bidders, a strategy of abstaining from the start of the contest will succeed and spread through the population.The inevitable consequence is that for those individuals who do not abstain right away, but wait a few seconds before abstaining, some of the benefits they might have accrued begin to accrue.This is an advantageous strategy used against individuals who have already dominated the population and retreated without a fight.Thus natural selection favors holding out for a period of time before abstaining, gradually extending the period until again as far as the real economic value of the resource in question will allow. In talking, we unknowingly describe the phenomenon of swaying in populations.Yet again, mathematical analysis shows that this wobble is not inevitable.There is an evolutionarily stable strategy, which can be expressed not only in mathematical formulas, but also in words: each individual confronts for a period of time that cannot be estimated in advance, that is, it is difficult to estimate in advance in any specific situation , but according to the actual value of the resource, a level structure can be obtained.For example, suppose the actual value of the resource is five minutes of stamina.In an evolutionarily stable strategy, any individual may last more than five minutes, or less than five minutes, or exactly five minutes.The important thing is that the other party has no way of knowing how long it is going to last on this particular occasion. In a war of attrition it is obviously of the utmost importance that the individual should not give any hint as to how long it intends to last.The mere twitch of a whisker at the mere thought of throwing in the towel puts any individual at a disadvantage at once.If a twitch of the whiskers is a sure sign of retreat in less than a minute, a very simple strategy for winning is this: If your opponent's whiskers twitch, no matter how long you're prepared to hold on in advance, you'll have more wait a minute.If your opponent's beard is not yet shaking, and it is less than a minute before you are ready to surrender, then you abstain immediately and don't waste any more time.Never shake your own beard.Thus, whisker shaking, or any similar exposure that heralds future behavior, is quickly punished by natural selection.A calm facial expression will be developed. Why keep a straight face instead of openly lying?The reason is again that the act of lying is unstable.Assuming that it is the case that in a war of attrition most individuals only bristle the nape when they really want to fight for a long time, then what would be able to develop is the obvious opposite strategy: when the opponent puffs up the nape Immediately throw in the towel.But this is when the ranks of liars may begin to build up.Individuals that really had no intention of fighting for a long time bristled the scruff of their necks in every confrontation, and the fruits of victory were easily reaped.The liar gene thus spreads.When liars become the majority, natural selection favors those individuals who can force the liars to a showdown.Thus the number of liars will decrease again.Neither lying nor telling the truth is an evolutionarily stable strategy in a war of attrition.The nonchalant facial expression is an evolutionarily stable strategy.Even if the final surrender, it will be sudden and unpredictable. So far we have considered only what Smith calls the symmetric race.意思是說，我們所作的假定是，競賽參加者除搏鬥策略之外，其餘一切方面的條件都是相等的。我們把鷹和鴿子假定為力量強弱相同，具有的武器和防護器官相同，而且可能贏得的勝利果實也相同。對於假設一種模式來說，這是簡便的，但並不太真實。帕克和史密斯也曾對不對稱的競賽進行了探討。舉例說，如果個體在身材大小和搏鬥能力方面各不相同，而每一個體也能夠對自己的和對手的身材大小進行比較並作出估計的話，這對形成的ESS是否有影響？肯定是有影響的。 不對稱現象似乎主要有三類。第一類就是我們剛才提到的那種情況：個體在身材大小或搏鬥裝備方面可能不同；第二類是，個體可能因勝利果實的多寡而有所區別。比如說，衰老的雄性動物，由於其餘生不會很長，如果受傷，它的損失較之來日方長的、精力充沛的年輕雄性動物可能要少。 第三類，純屬隨意假定而且明顯互不相干的不對稱現象能夠產生一種ESS，因為這種不對稱現象能夠使競賽很快見分曉，這是這種理論的一種異乎尋常的推論。比如說，通常會發生這樣的情況，即兩個競爭者中的一個比另一個早到達競賽地點。我們就分別稱它們為留駐者（resident）和闖入者（intruder）。為了便於論證起見，我是這樣進行假定的，不論是留駐者還是闖入者都不因此而具有任何附加的有利條件。我們將會看到，這一假定在實際生活中可能與事實不符，但這點並不是問題的關鍵。問題的關鍵在於，縱令留駐者具有優於闖入者的有利條件這種假定無理可據，基於不對稱現象本身的ESS也很可能會得以形成。簡單地講，這和人類拋擲錢幣，並根據錢幣的正反面來迅速而毫不用爭執地解決爭論的情況有類似之處。 如果你是留駐者，進攻；如果你是闖入者，退卻，這種有條件的策略能夠成為ESS。由於不對稱現象是任意假定的，因此，如果是留駐者，退卻；如果是闖入者，進攻這種相反的策略也有可能是穩定的。具體種群中到底採取這兩種ESS中的哪一種，這要取決於其中的哪一種ESS首先達到多數。個體的大多數一旦運用這兩種有條件的策略的某一種，所有脫離群眾的行為皆受到懲罰，這種策略就因之稱為ESS。 譬如說，假定所有個體都實行留駐者贏，闖入者逃的策略。就是說它們所進行的搏鬥將會是輸贏各半。它們絕不會受傷，也絕不會浪費時間，因為一切爭端都按任意作出的慣例迅速得到解決。現在讓我們設想出現一個新的突變型叛逆者。假定它實行的是純粹的鷹的策略，永遠進攻，從不退卻，那麼它的對手是闖入者時，它就會贏；而當它的對手是留駐者時，它就要冒受傷的很大風險。平均來說，它比那些按ESS的任意規定的準則進行比賽的個體，得分要低些。如果叛逆者不顧慣常的策略而試圖反其道而行之，採取如身為留駐者就逃；如身為闖入者就進攻的策略，那麼它的下場會更糟。它不僅時常受傷，而且也極少有機會贏得一場競賽。然而，假定由於某些偶然的變化，採用同慣例相反的策略的個體竟然成了多數，這樣它們的這種策略就會成為一種準則，偏離它就要受到懲罰。可以想見，我們如果連續觀察一個種群好幾代，我們就能看到一系列偶然發生的從一種穩定狀態跳到另一種穩定狀態的現象。 但是實際生活中可能並不存在真正的任意不對稱現象。如留駐者實際上可能比闖入者享有更有利的條件，因為它們對當地的地形更熟悉。闖入者也許更可能是氣喘吁吁的，因為它必須趕到戰鬥現場，而留駐者卻是一直待在那裡的。兩種穩定狀態中，留駐者贏，闖入者退這種狀態存在於自然界的可能性更大，其所以如此的理由是比較深奧的。這是因為闖入者贏，留駐者退這種相反的策略有一種固有的自我毀滅傾向，史密斯把這種策略稱為自相矛盾的策略。處於這種自相矛盾中的ESS狀態的任何種群中，所有個體總是極力設法避免處於留駐者的地位：無論何時與對手相遇，它們總是千方百計地充當闖入者。為了做到這一點，它們只有不停地四處流竄，居無定所。It's pointless.這種進化趨勢，除無疑會招致時間和精力上的損失之外，其本身往往導致留駐者這一類型的消亡。在處於另一種穩定狀態，即留駐者贏，闖入者退的種群中，自然選擇有利於努力成為留駐者的個體。對每一個體來說，就是要堅守一塊具體地盤，盡可能少離開，而且擺出保衛它的架勢。這種行為如大家所知，在自然界中到處可見，大家把這種行為稱為領土保衛。 就我所知，偉大的個體生態學家廷伯根（Niko Tinbergen）所作的異常巧妙和一目了然的試驗，再精采不過地展示了這種行為上的不對稱性。他有一隻魚缸，其中放了兩條雄性刺魚。它們在魚缸的兩端各自做了巢，並各自保衛其巢穴附近的水域。廷伯根將這兩條刺魚分別放入兩個大的玻璃試管中，再把兩個試管並排放一起，只見它們隔著玻璃管試圖相互搏鬥。於是產生了十分有趣的結果。當他將兩個試營移到刺魚A的巢穴附近時，A就擺出進攻的架勢，而刺魚B就試圖退卻；但當他將兩個試管移到刺魚B的水域時，因主客易地而形勢倒轉。廷伯根只要將兩個試管從魚缸的一端移向另一端，他就能指揮哪條刺魚進攻，哪條退卻。很顯然，兩條刺魚實行的都是簡單的有條件策略：凡是留駐者，進攻；凡是闖入者，退卻。 這種領土行為有什麼生物學上的好處？這是生物學家時常要問的問題，生物學家提出了許多論點，其中有些論點稍後我們將會提及。但是我們現在就可以看出，提出這樣的問題可能本來就是不必要的。這種領土保衛行為可能僅僅是由於抵達時間的不對稱性而形成的一種ESS，而抵達時間的不對稱性通常就是兩個個體同一塊地盤之間關係的一種特點。 體積的大小和一般的搏鬥能力，據認為是非任意性不對稱現象中最重要的形式。體積大不一定就是贏得搏鬥不可或缺的最重要特性，但可能是特性之一。如果兩個個體搏鬥時比較大的一個總是贏的話，如果每一個體都能確切知道自己比對手大還是小，只有一種策略是明智的：如果你的對手比你體積大，趕快逃跑。同比你體積小的人進行搏鬥。假使體積的重要性並不那麼肯定，情況也就隨之更複雜些。如果體積大還是具有一點優越性的話，我剛才講的策略就仍舊是穩定的。如果受傷的風險很大的話，還可能有一種似非而是的策略，即專挑比你大的人進行搏鬥，見到比你小的就逃！稱之為似非而是的原因是不言而喻的。因為這種策略似乎完全違背常識。它之所以能夠穩定，其原因在於：在全部由似非而是的策略者組成的種群中，絕不會有人受傷，因為每場競賽中，逃走的總是參加競賽的較大的一個。一個大小適中的突變體如實行的是合理的策略，即專挑比自己體積小的對手，他就要同他所遇見的人中的一半進行逐步加劇的嚴重搏鬥。因為，如果他遇到比自己小的個體，他就進攻；而較小的個體拚命還擊，因為後者實行的是似非而是策略；儘管合理策略的實行者比似非而是策略的實行者贏得勝利的可能性更大一些，但他仍舊冒著失敗和嚴重受傷的實際風險。由於種群中的大部分個體實行似非而是的策略，因而一個合理策略的實行者比任何一個似非而是策略的實行者受傷的可能性都大。 即使似非而是的策略可能是穩定的，但它大概只具有學術上的意義。似非而是策略的搏鬥者只有在數量上大大超過合理策略的搏鬥者的情況下才能獲得較高的平均盈利。首先，這樣的狀況如何能夠出現實屬難以想像。即使出現這種情況，合理策略者對似非而是策略者的比率也只要略微向合理策略者一邊移動一點，便達到另一種ESS合理的策略的引力區域（zone of attraction）。所謂引力區域即種群的一組比率，在這個例子裡，合理策略者處於這組比率的範圍內時是有利的：種群一旦到達這一區域，就不可避免地被引向合理的穩定點。要是在自然界能夠找到一個似非而是的ESS實例會是一件令人興奮的事情，但我懷疑我們能否抱這樣的侈望（我話說得太早了。在我寫完了上面這句話之後，史密斯教授提醒我注意伯吉斯（Burgess）關於墨西哥群居蜘蛛oecobius civitas（擬壁錢屬）的行為所作的下述描繪如果一隻蜘蛛被驚動並被趕出其隱避的地方，它就急沖沖地爬過岩石，如岩石上面無隙縫可藏身，就可能到同一物種的其他蜘蛛的隱蔽地點去避難。如果闖入者進來時，這個蜘蛛正在家裡，它並不進攻，而是急沖沖爬出去再為自己去另尋新的避難所。因此，一旦第一個蜘蛛被驚動，從一個蜘蛛網到另一個蜘蛛網的一系列替換過程要持續幾秒鐘，這種情況往往會使聚居區的大部分蜘蛛從它們本來的隱蔽所遷徙，到另一隻蜘蛛的隱蔽所（群居蜘蛛，《科學美國人》，一九七六年三月號）。這就是第一百零九頁上所講的那種意義上的似非而是的現象）。 假如個體對以往搏鬥的結果保留某些記憶，情況又會是怎樣呢？這要看這種記憶是具體的還是一般的。蟋蟀對以往搏鬥的情況具有一般的記憶。一隻蟋蟀如果在最近多次搏鬥中獲勝，它就會變得更具有鷹的特點；而一隻最近連遭敗北的蟋蟀，其特點會更接近鴿子。亞歷山大（R．D．Alexander）很巧妙地證實了這種情況，他利用一個模型蟋蟀痛擊真正的蟋蟀。吃過這種苦頭的蟋蟀再同其他真正的蟋蟀搏鬥時多數要失敗。我們可以說，每個蟋蟀在同其種群中有平均搏鬥能力的成員作比較的同時，對自己的搏鬥能力不斷作出新的估計。如果把對以往的搏鬥情況具有一般記憶的動物，如蟋蟀，集中在一起組成一個與外界不相往來的群體，過一段時間之後，很可能會形成某種類型的統治集團。觀察者能夠把這些個體按級別高低的順序排列。在這一順序中級別低的個體通常要屈從於級別高的個體。這倒沒有必要認為這些個體相互能夠辨認。習慣於贏的個體就越是會贏，習慣於失敗的個體就越是要失敗。實際情況就是如此。即使開始時個體的勝利或失敗完全是偶然的，它們會自動歸類形成等級。這種情況附帶產生了一個效果：群體中激烈的搏鬥逐漸減少。 我不得不用某種類型的統治集團這樣一個名稱，因為許多人只把統治集團（dominance hierarchy）這個術語用於個體具有相互辨認能力的情況。在這類例子中，對於以往搏鬥的記憶是具體的而不是一般的。作為個體來說，蟋蟀相互辨認不出，但母雞和猴子都能相互辨認。如果你是一個猴子的話，一個過去曾經打敗過你的猴子，今後還可能要打敗你。對個體來說，最好的策略是，對待先前曾打敗過它的個體應採取相對的帶有鴿派味道的態度。如果我們把一群過去相互從未見過的母雞放在一起，通常會引起許多搏鬥。一段時間之後，搏鬥越來越少，但其原因同蟋蟀的情況不同。對母雞來說，搏鬥減少是因為在個體的相互關係中，每一個體都能安分守己。這對整個群體來說也帶來好處，下面的情況足資證明：有人注意到，在已確立的母雞群體中，很少發生兇猛搏鬥的情況，蛋的產量就比較高；相比之下，在其成員不斷更換因而搏鬥更加頻繁的母雞群體中，蛋產量就比較低。生物學家常常把這種統治集團在生物學上的優越性或功能說成是在於減少群體中明顯的進犯行為。然而這種講法是錯誤的。不能說統治集團本身在進化的意義上具有功能，因為它是群體而不是個體的一種特性。通過統治集團的形式表現出來的個體行為模式，從群體水平的觀點上來看，可以說是具有功能的。然而，如果我們根本不提功能這個詞，而是按照存在有個體辨認能力和記憶的不對稱競賽中的各種ESS來考慮這個問題，這樣甚至會更好些。 迄今我們所考慮的競爭都是指同一物種的成員間的競爭。物種間的競爭情況又是如何呢？我們上面已經談過，不同物種的成員之間的競爭，不像同一物種的成員之間那樣直接。基於這一理由，我們應該設想它們有關資源的爭端是比較少的，我們的預料已得到證實。例如，知更鳥保衛地盤不准其他知更鳥侵犯，但對大山雀卻並不戒備。我們可以畫一幅不同個體知更鳥在樹林中分別佔有領地的地圖，然後在上面疊上一幅個體大山雀領地地圖，可以看到兩個物種的領地部分重疊，完全不相互排斥，它們簡直像生活在不同的星球上。 但不同物種的個體之間也要發生尖銳的利害衝突，不過其表現形式不同而已。例如，獅子想吃羚羊的軀體，而羚羊對於自己的軀體卻另有截然不同的打算。雖然這種情況不是通常所認為的那種爭奪資源的競爭，但從邏輯上說，不算競爭資源，道理上難以講通。在這裡，有爭議的資源是肉。獅子的基因想要肉供其生存機器食用，而羚羊的基因是想把肉作為其生存機器進行工作的肌肉和器官。肉的這兩種用途是互不相容的，因此就發生了利害衝突。 同一物種的成員也是肉做的，但為什麼同類相食的情況相對來說這樣少呢？這種情況我們在黑頭鷗中見到過，成年鷗有時要吃自己物種的幼鷗。但我們從未見到成年的肉食動物為吞食自己物種的其他成年動物而主動去追逐它們。為什麼沒有這種現象呢？我們仍舊習慣於按照物種利益的進化觀點去思考問題，以致我們時常忘記擺出這樣完全有道理的問題：為什麼獅子不去追捕其他獅子？還有一個人們很少提出的其實是很好的問題：羚羊為什麼見到獅子就逃，而不進行回擊呢？ 獅子之所以不追捕獅子是因為那樣做對它們來說不是一種ESS。同類相食的策略是不穩定的，其原因和前面所舉例子中的鷹策略相同。遭到反擊的危險性太大了。而在不同物種的成員之間的競爭中，這種反擊的可能性要小些，這也就是那麼多的被捕食的動物要逃走而不反擊的道理。這種現象可能源出於這樣的事實：在不同物種的兩隻動物的相互作用中存在一種固有的不對稱現象，而且其不對稱的程度要比同一物種的成員之間大。競爭中的不對稱現象凡是強烈的，ESS一般是以不對稱現象為依據的有條件的策略。如果你比對手小，就逃走；如果你比對手大，就進攻，這種類型的策略很可能在不同物種成員之間的競爭中得到發展，因為可以利用的不對稱現象非常之多。獅子和羚羊通過進化上的趨異過程而形成了一種穩定性，而競爭中本來就有的不對稱現象也因此變得日益加強。追逐和逃跑分別變成它們各自的高超技巧。一隻突變型羚羊如果採取了對峙並搏鬥的策略來對付獅子，它的命運同那些消失在地平線上的其他羚羊相比，可能要不妙得多。 我總是有一種預感，我們可能最終會承認ESS概念的發明，是自達爾文以來進化理論上最重要的發展之一。凡是有利害衝突的地方，它都適用，這就是說幾乎在一切地方都適用。一些研究動物行為的學者沾染了侈談社會組織的習慣。他們動輒把一個物種的社會組織看作是一個具備作為實體的條件的單位，它享有生物學上的有利條件。我所舉的統治集團就是一例。我相信，混跡於生物學家有關社會組織的大量論述中的那些隱蔽的群體選擇主義的各種假定，是能夠辨認出來的。史密斯的ESS概念使我們第一次能夠清楚地看到，一個由許多獨立的自私實體所構成的集合體，如何最終變得像一個有組織的整體。我認為，這不僅對物種內的社會組織是正確的，而對於由許多物種所構成的生態系統以及群落也是正確的。從長遠觀點來看，我預期ESS概念將會使生態學發生徹底的變革。 我們也可以把這一概念運用於曾在第三章擱置下來的一個問題，即船上的槳手（代表體內的基因）需要很好的集體精神這一類比。基因被選擇，不是因為它在孤立狀態下的好，而是由於在基因庫中的其他基因這一背景下工作得好。好的基因應能夠和它必須與之長期共同生活於一系列個體內的其餘基因和諧共存，相互補充。磨嚼植物的牙齒的基因在草食物種的基因庫中是好基因，但在肉食物種的基因庫中就是不好的基因。 我們可以設想一個不矛盾的基因組合，它是作為一個單位被選擇在一起的。在第三章蝴蝶模擬的例子中，情況似乎就是如此。但現在ESS概念使我們能夠看到，自然選擇純粹在獨立基因的水平上如何能夠得到相同的結果，這就是ESS概念的力量所在。這些基因並不一定是在同一條染色體上連接在一起的。 其實，划船的類比還沒達到說明這一概念的程度。它最多只能說明一個近似的概念。我們假定，一個賽艇的全體船員要能真正獲得成功，重要的是獎手必須用言語協調其動作。我們再進一步假定，在槳手庫中，教練能夠選用的槳手，有些只會講英語，有些只會講德語。操英語的獎手並不始終比操德語的槳手好些，也不總是比操德語的槳手差些。但由於通話的重要性，混合組成的槳手隊得勝的機會要少些，而純粹講英語的或純粹講德語的所組成的槳手隊得勝的機會要多些。 教練沒有認識到這點，他只是任意地調配他的槳手，認為得勝的船上的個體都是好的，認為失敗的船上的個體都是差的。如果在教練的槳手庫中，英國人碰巧占壓倒優勢，那麼，船上只要有一個德國人，很可能就會使這條船輸掉，因為無法進行通話；反之，如果在槳手庫中湊巧德國人佔絕對優勢，船上只要有一個英國人，也會使這條船失敗。因此，最理想的一隊船員應處於兩種穩定狀態中任何一種，即要麼全部是英國人，要麼全部是德國人，而絕不是混合陣容。表面上看起來，教練似乎選擇清一色的語言小組作為單位，其實不然，他是根據個體槳手贏得競賽的明顯能力來進行選擇的。而個體贏得競賽的趨向則要取決於候選槳手庫中現有的其他個體。屬於少數的候選槳手會自動受到懲罰，這倒並非因為他們是不好的槳手，而僅僅是由於他們是少數而已。同樣，基因因能相互和諧共存而被選擇在一起，這並不一定說明我們必須像看待蝴蝶的情況那樣，把基因群體也看成是作為單位來進行選擇的。在單個基因低水平上的選擇能給人以在某種更高水平上選擇的印象。 在這一例子中，自然選擇有利於簡單的行為一致性。更為有趣的是，基因之被選擇可能由於它們的相輔相成的行為。以類比法來說明問題，我們可以假定由四個右手划槳手和四個左手划槳手組成的賽艇隊是力量勻稱的理想隊；我們再假定教練不懂得這個道理，他根據功績盲目進行挑選。那麼如果在候選槳手庫中碰巧右手划槳手占壓倒優勢的話，任何個別的左手划槳手往往會成為一種有利因素：他有可能使他所在的任何一條船取得勝利，他因此就顯得是一個好槳手。反之，在左手划槳手佔絕對多數的槳手庫中，右手划槳手就是一個有利因素。這種情況就同一隻鷹在鴿子種群中取得良好成績，以及一隻鴿子在鷹種群中取得良好成績的情況相似。所不同的是，在那裡我們講的是關於個體自私的機器之間的相互作用；而這裡我們用類比法談論的是關於體內基因之間的相互作用。 教練盲目挑選好槳手的最終結果必然是由四個左手划槳手和四個右手划槳手組成的一個理想的槳手隊。表面看起來他好像把這些槳手作為一個完整的、力量勻稱的單位選在一起的。我覺得說他在較低的水平上，即在單獨的候選槳手水平上進行選擇更加簡便省事。四個左手划槳手和四個右手划槳手加在一起的這種進化上穩定狀態（策略一詞在這裡會引起誤解）的形成，只不過是以表面功績為基礎在低水平上進行選擇的必然結果。 基因庫是基因的長期環境。好的基因是作為在基因庫中存活下來的基因盲目地選擇出來的。這不是一種理論，甚至也不是一種觀察到的事實，它不過是一個概念無數次的重複。什麼東西使基因成為好基因才是人們感興趣的問題。我曾講過，建造高效能的生存機器軀體的能力是基因之成為好基因的標準，這是一種初步的近似講法。現在我們必須對這種講法加以修正。基因庫是由一組進化上穩定的基因所形成，這組基因成為一個不受任何新基因侵犯的基因庫。大部分因突變、重新組合或來自外部而出現的基因很快就受到自然選擇的懲罰：這組進化上穩定的基因重新得到恢復。新基因侵入一組穩定的基因偶爾也會獲得成功，即成功地在基因庫中散佈開來。然後出現一個不穩定的過渡階段，最終又形成新的一組進化上穩定的基因發生了某種細微程度的進化。按進犯策略類推，一個種群可能有不止一個可選擇的穩定點，還可能偶爾從一個穩定點跳向另一個穩定點。漸進的進化過程與其說是一個穩步向上爬的進程，倒不如說是一系列的從一個穩定台階走上另一個穩定台階的不連續的步伐。作為一個整體，種群的行為就好像是一個自動進行調節的單位。而這種幻覺是由在單個基因水平上進行的選擇所造成。基因是根據其成績被選擇的，但對成遺的判斷是以基因在一組進化上穩定的基因（即現存基因庫）的背景下的表現為基礎的。 史密斯集中地論述了一些完整個體之間的進犯性相互作用，從而把問題闡明。鷹的軀體和鴿子軀體之間的穩定比率易於想像，因為軀體是我們能夠看得見的大物體。但寄居於不同軀體中的基因之間的這種相互作用猶如冰山的尖頂。而在一組進化上穩定的基因基因庫中，基因之間絕大部分的重要相互作用，是在個體的軀體內進行的。這些相互作用很難看見，因為它們是在細胞內，主要是在發育中的胚胎細胞內發生的。完整的渾然一體的軀體之所以存在，正是因為它們是一組進化上穩定的自私基因的產物。 但我必須回到完整動物之間的相互作用的水平上來，因為這是本書的主題。把個體動物視為獨立的自私機器便於理解進犯行為。如果有關個體是近親兄弟姐妹，堂兄弟姐妹，雙親和子女這一模式也就失去效用。這是因為近親體內有很大一部分基因是共同的。因此，每一個自私的基因卻同時須忠於不同的個體。這一問題留待下一章再加闡明。