Chapter 10 Chapter Eight: The Battle Between Generations

Let's start by addressing the first question posed at the end of the previous chapter.Should mothers have pets?Should she treat her children equally and not favor one another?As tiresome as it may be to say, I think it is necessary to babble a little more, and make a statement as usual, so as to avoid misunderstanding.The word darling carries no subjective connotations, and the word ought carries no moral imperatives.I view motherhood as a survival machine programmed to reproduce as many copies of the genes as possible in the body.You and I are human beings who know what it is to have a conscious purpose, so it is convenient for me to use purposeful language as a metaphor in explaining the behavior of survival machines .

What do we actually mean when we say that a mother has a favorite?This means that when it invests in its children, its resources are often distributed unequally.The resources a mother can invest in include many things.Food is the obvious one; also includes the energy expended to acquire it, since it has to pay a certain price to get it.The risk it takes to protect its offspring from predators is also a resource that it can spend or refuse to spend.In addition, the energy and time spent on household chores, weather protection, and, in some species, parenting are valuable resources.Mothers are free to decide how to distribute these resources among their children, either equally or unequally.

It is difficult to conceive of a currency as the unit of measure for all the resources the parents invest.Just as human societies use money as a currency that can be converted into food, land, or labor time at any time, we need a currency to measure these resources, the resources that individual survival machines use to invest in another individual, especially their own children.Certain units of measure of energy, such as the calorie, have merit and some ecologists have engaged in accounting for the cost of energy consumption in nature.But this accounting is incomplete because it cannot be accurately converted into a currency of practical significance, namely evolution's gold standard genetic survival.1972 Trivers proposed the concept of parental investment.and so neatly solves the problem (although reading his terse essay, we get the impression between the lines that this formulation is on par with Sir Ronald Fisher, the greatest biologist of the twentieth century. Parental expenditure, introduced in 1930, is very similar in meaning).

Parental investment (P.I) is defined as any form of investment by a parent in an individual offspring that increases the individual's chances of surviving (and thus successfully reproducing) at the expense of other parental investments in the offspring. individual's ability to invest.The beauty of Trivers' concept of parental investment is that it is measured in very close to meaningful units.A baby consumes a certain amount of mother's milk, measured not in calories or pints, but in units of damage to other babies from the same mother.For example, if a mother has two babies, x and y, and x eats a pint of breast milk, which in turn represents a major part of the parental investment, then the unit of measure is y for not eating the pint. A pint of breast milk increases the likelihood of his death.Parental investment is measured in terms of shortening the life expectancy of other children, both born and unborn.

Parental investment is not a perfect calculation because it overemphasizes the importance of parents and relatively devalues ​​other genetic relationships.The most ideal should be the conceptual unit of measurement of altruism investment.We say that individual A invests in individual B, meaning that individual A increases individual B's chances of survival, but at the expense of individual A's ability to invest in other individuals, including itself, all at the cost of Calculations are weighted by the appropriate kinship index.In this way, when calculating the amount of investment a mother has in any child, it is best to use the damage to the life expectancy of other individuals as the unit of measurement. The so-called other individuals refer not only to other children of the mother, but also nephews, nephews, Nieces, nieces, and the mother herself, etc.However, in many respects, this approach is too cumbersome to solve practical problems.However, Trivers' calculation method still has high practical value.

There is a certain amount of parental investment that any mother can use in her children (and other relatives, herself, etc., but for the sake of argument, we only consider children here) in her lifetime.This total parental investment includes all the food she can collect or produce during her lifetime, all the risks she is prepared to take, and all the energy and energy she can expend for the welfare of her children.How should a young female invest her life resources in adulthood?What kind of investment strategy is the best policy it should follow?Lacker's theory already tells us that it should not spread resources among so many children that each child gets a disproportionately small share.It would lose too many genes in doing so: it wouldn't have enough grandchildren.On the other hand, it should not concentrate its resources on a few spoiled children.It actually secures a certain number of grandchildren, but some of its rivals end up producing more grandchildren by investing in the optimum number of children.So much for the investment strategy of egalitarianism.We are now interested in whether it is beneficial for a mother not to invest in her children equally, that is, whether she should have favourites.

We say that there is no genetic basis for mothers not treating their children equally.It has the same relationship index with each child, which is one/two.The ideal strategy for it is to raise as many children as it can, but to invest equally until they start producing males and females of their own.However, as we have seen above, some individuals are more desirable life insurance than others.A litter of short, stunted litters has the same number of genes from the mother as its otherwise normally developing litter counterparts.But its estimated lifespan is shorter.In other words, it needs additional parental investment if it is to live as long as its brethren.A mother can decide on a case-by-case basis, and she may find it pays to refuse to raise a small, stunted young animal and give her siblings all of her share of the parental investment due to her name.In fact, it may sometimes pay for the mother to simply throw it away as food for other young animals, or eat it herself as raw material for making milk.The sow sometimes devours the piglets, but whether she preys on the smaller ones I don't know.

Stunted small animals are a special case.We can make some more general guesses about how the age of the young affects the mother's propensity to invest.If it can save only one of two young children, and the other will eventually die, it should save the older one.This is because if the older one dies instead of the younger brother, a greater portion of his lifetime parental investment will be lost.Maybe it's better to say that if it saves the little brother, it still needs to expend some expensive resources to raise the toddler to the age of the big brother. On the other hand, if the choice is not explicitly a matter of life or death, it may be better for the mother to gamble on the younger one.We may take the example of a mother who is in a dilemma because she does not know whether to give some food to the younger ones or to the older ones.Big brothers are more likely to forage for food on their own.So if the mother doesn't feed it, it doesn't necessarily die from it.On the other hand, the little brother is too young to find food by himself. If the mother gave the food to the big brother, the little brother is more likely to starve to death.In such a case, even if the mother would rather sacrifice the younger brother, she might still feed the younger brother, since the older brother is unlikely to starve to death after all.This is exactly why mammals wean their young, instead of feeding them for life.At some point, it is wise for a mother to stop feeding a young child and reserve its resources for future offspring.When this time comes, the mother will wean the infant.Sometimes a female animal may know that it is the last calf she has to give birth to, and she will spend all of her life's resources on the smallest young, perhaps suckling the young to adulthood.It should, however, weigh whether it would be more profitable to spend its resources on grandchildren or nephews, who, although only half as related to it as their children, are likely to benefit from the investment more than their children. It's more than twice the size of the toddler itself.

Here it seems appropriate to mention the puzzling phenomenon known as menopause.That is, the phenomenon of the sudden disappearance of the reproductive ability of human middle-aged women.In our savage ancestors, this condition may have been relatively rare, because not many women lived to the age of menopause.However, the apparent difference between a woman's physiological mutation and a man's gradual loss of fertility suggests that menopause may have some genetic purpose, that is, it is an adaptation.It is not easy to clarify this issue.At first glance, we might well think that a woman should keep having sons and daughters before she dies, even though as she gets older the chances of her babies surviving become lower and lower.At least, they should always do their best, right?But we should remember that her grandchildren are also her descendants, though only half as related.

For various reasons, perhaps connected with Medawar's doctrine of senescence (p. 54), women in a state of nature gradually lose their ability to raise children as they grow older.As a result, children born to older mothers have a shorter life expectancy than children born to young mothers.This means that if a woman and her daughter give birth on the same day, her grandson's life expectancy will probably be longer than her son's life expectancy.After a woman reaches a certain age, the average chance of each of her children surviving to adulthood is less than half the average chance of surviving to adulthood for her grandchildren of the same age.At this time, genes that choose grandchildren over children as investments tend to flourish.Only one in four grandchildren has the gene, and one in two children has its allele.But grandchildren enjoy a longer life expectancy, a positive factor that outweighs the quantitative disadvantage.Thus, the gene for grandchildren's altruistic behavior prevails in the gene pool.A woman cannot focus on investing in her grandchildren if she continues to bear children herself.Thus, there are more and more genes that make the mother infertile in middle age.This is because the grandchild Hugh has these genes, and the grandmother's altruistic behavior promotes the grandchild's survival.

This may be the reason for the formation of women's menopause.The reason why male fertility declines gradually rather than suddenly is probably because fathers do not invest as much in each child as mothers do.Even for an old man, it pays to invest in children rather than grandchildren, so long as he can still procreate young women. So far, in this and the last chapter, we have looked at everything from the point of view of the parent, mainly the mother.We've asked questions like: Should parents have favorites, and generally speaking, what's the ideal investment strategy as far as the father or mother is concerned?However, as parents invest in their offspring, each young child may be able to exert influence over the parents for additional care.Even if parents don't want to show favoritism among their children, shouldn't the children be the first to act first and grab more things?Are they doing themselves any good?More strictly speaking, would genes that predispose children to plunder for selfish purposes to become more numerous in the gene pool than alleles that merely cause children to accept their fair share?Trivers brilliantly analyzed this problem in a 1974 paper entitled Parent-offspring Conflict. A mother is equally related to her present and unborn children.We have learned that, from a purely genetic point of view, it should have no favourites.If it actually has a preference, it's because of differences in life expectancy due to age or other differences.As far as relatedness is concerned, a mother, like any individual, is twice as close to herself as she is to any of her children.With other conditions unchanged.This means that it is entitled to selfishly monopolize most of its resources, other things being equal.So if it can spend a substantial portion of its resources on offspring, that will do its genes a greater good.This is because the children are younger and more needy than him, so they must benefit more from each unit of investment than he himself does.Genes that promote investment in individuals who are more in need rather than in themselves can gain an advantage in the gene pool, even if the beneficiary has only some of the individual's genes.This is why animals exhibit parental altruism, and indeed why they exhibit any form of kin selection. Let us now look at this question from a young child's point of view.In relation to any one of its brothers or sisters it is exactly as closely related to any one of its brothers or sisters as its mother is to her children.The kinship index is all one/two.It thus expects its mother to invest a portion of its resources in its brother or sister.Genetically, both he and his mother want to work for the good of its siblings, and they do so to an equal degree.But, as I said above, he is twice as close to himself as he is to any of his siblings, so, other things being equal, he would expect his mother to invest in him a little more .In this case, other things may in fact remain the same.If you and your brother are the same age and benefit equally from a pint of mother's milk, you should try to grab a larger than your fair share, and your brother should try to grab a bigger share than your older brother deserves. share of breast milk.You must have seen a litter of piglets screaming and scrambling to get to the sow when she was lying down to nurse.You've seen a group of little boys fighting for the last piece of cake.Selfishness and greed seem to be characteristic of young children's behavior. But the problem is not that simple.If I'm competing with my brother for a morsel and he's much younger than me, it's definitely going to be better for him than it is for me, so it might pay off my genes to give him the morsel of.Brotherly and parental altruism can have exactly the same basis.As I said before, the relatedness index of both is one/two, and younger individuals are always able to make better use of this resource than older ones.If I have the gene for food humility, there's a 50 percent chance my penis has it.Even though I have a 100% greater chance of having this gene in me than my brother because the gene is definitely in me, I probably don't need this food half as badly.In general, a young child should grab more than his fair share of parental investment, but only in moderation.How can enough be enough?The net loss of its surviving and unborn brothers or sisters due to its grabbing of food.cannot be greater than twice the benefit it derives from it. Let's consider the question of when is the best time to wean.A mother who is planning to wean a nursing toddler in preparation for a second child.The toddler, on the other hand, does not wish to be weaned so quickly, since breast milk is a convenient, low-effort source of food, and he does not want to travel to make ends meet.Rather, he eventually wants to go out and earn a living, but only if his mother is free to raise his younger siblings, thus doing his genes a greater good.A toddler gets less and less relative benefit from each pint of breast milk as he gets older.This is because as he grows larger, a pint of breast milk becomes smaller and smaller in proportion to his needs, and because he has a greater ability to live independently if necessary.Thus, when an older toddler consumes a pint of breast milk that would have been given to a younger toddler, it consumes a relatively greater parental investment than a younger toddler consumes the pint. Parental investment consumed by weaning.In the course of every young child's development, there must come a time when its mother stops feeding it and it is advantageous to invest in a newborn child.Otherwise, after some time, older infants are also automatically weaned in order to maximize the benefits of their genes.At this point, a pint of mother's milk does more good for the copies of its genes that might exist in its younger siblings than it does for the genes that actually exist in itself. The contradiction that exists between mother and child is not absolute but relative.In this example, the contradiction involves only timing issues.The mother intends to continue feeding the infant until it has received its fair share of the total investment spent on it.This entitlement depends on the child's estimated lifespan and the amount of parental investment already spent on it.So far, the contradiction has not yet arisen. Similarly, it is not appropriate for a baby to be suckled for too long. When the loss suffered by its unborn siblings due to it continuing to suckle exceeds twice the benefit it gains from it, it should not Keep eating; mother and child are on the same page on this one.But the conflict arises in the intervening period when, in the eyes of the mother, the infant is getting more than its fair share, and the younger siblings have not yet lost twice as much as it has benefited. Weaning time is just one example of what can cause arguments between mother and child.We can also see the situation as a dispute between an individual and all his unborn siblings who are protected by the mother.However, more direct disputes may occur between sibling rivals, or between nest mates, in order to compete for parental investment.So mothers usually try to be fair. Many birds raise their young in nests.The chicks chirp while the mother drops worms or other food into the gaping mouths.It stands to reason that the size of a chick's cry is directly proportional to its hunger.If the hen always feeds the one who crows the loudest first, sooner or later each chick will get its fair share, for a well-fed chick will stop yelling.This is the case, at least in the best of circumstances.In this environment, everyone follows the rules and does not falsify.But according to our selfish gene concept, we must estimate that individuals will cheat and pretend to be hungry.This escalation of deception obviously does not have the desired effect, because if all the chicks yelled and pretended to be starving, the yelling would become the norm and would not achieve the desired effect. The effect of lying.However, upgrading is easy and downgrading is difficult. No matter which chick takes the lead in lowering its voice, it will get less food, and it may really starve to death.Besides, for various reasons, birds do not raise their voices endlessly.For example, shouting too loudly consumes energy and attracts predators. We know that in a litter sometimes a small individual appears, much smaller than the rest.It is not as energetic as other young animals for food, so it often starves to death.We have considered under what conditions it would actually pay for the mother to let the little one die.If we judge by intuition alone, we probably always think that the little man himself will struggle to the last moment, but this inference may not be tenable in theory.Once a small child is so emaciated that its estimated lifespan is shortened to such an extent that it benefits less than half as much from the same amount of parental investment as other young children, then it is honorable and willing to die.In this way, its genes can benefit instead.In other words, a gene sends out the instruction: Hey, if you are much smaller than your flesh and blood brothers, then you don't have to fight, just die!This gene will succeed in the gene pool because it has an inherently small chance of surviving in a small individual, whereas it has a fifty percent chance of being present in each of the saved siblings.There is a point of no return in the little man's life voyage.Until this critical point is reached, it should try to survive, but once it has reached the critical point, it should stop struggling and would rather allow itself to be eaten by its siblings or parents. I did not speak of the above when we discussed Lack's theory of brood size.But if the mother bird is not sure how many eggs to incubate this year is the optimal amount, she can adopt the following wise strategy.It may incubate one more egg than it actually thinks may be optimum.In this way, if the food harvest this year is better than originally estimated, it will raise an extra child.Otherwise, it abandons the child to reduce losses.A mother bird always consciously feeds her brood in the same order, for example, feeding the chicks in order of size.In this way he can let one of them, perhaps the little one, die quickly without wasting too much food on him besides the first investment of egg yolk or its equivalent.From the mother bird's point of view, this explains the reason for the smallness phenomenon.The life of the little one is the wager of the mother bird, which is common among many birds, and is of the same nature as the buying and selling strategy on the Exchange. We liken animals to survival machines, behaving as if they purposely preserve their own genes.In this way we can speak of the contradiction between parent and offspring, that is, the struggle between two generations.This is a delicate struggle, where both sides go all out and are not bound by any rules and regulations.Young children take every opportunity to cheat.It will pretend to be hungrier than it is, perhaps younger or in greater danger than it is.Although the child is too young and weak to bully its parents, it does not hesitate to use all possible psychological tactical weapons: lying, coaxing, deceiving, exploiting, and even abusing kinship to behave against its relatives.On the other hand, parents must be vigilant against such deceptions and try their best to avoid being deceived.It does not seem to be difficult to do this.Knowing that her chick might be pretending to be hungry, a mother bird can respond with a feeding ration strategy, even if the chick continues to yell and yell.The problem is that the chick is probably not lying, but really hungry.If it dies from lack of food, the hen loses some of its precious genes.Wild birds can die after just a few hours of starvation. A. Zahavi (A. Zahavi) pointed out that there is a particularly terrible blackmail method of young children: it makes loud noises to deliberately attract predators.It is saying: Fox, fox, come and eat me!The parents had to plug its mouth with food.In this way, it gets extra food, but at its own risk.This unscrupulous tactic is the same one used by those who hijacked airliners.He threatened to blow up the plane unless he was paid a ransom, and he was prepared to die with it.I doubt that this strategy is good for evolution, not because it is too ruthless, but I think this strategy will end up doing more harm than good to blackmailing chicks.If it does attract a predator, its loss will be greater.Not to mention if it happens to be an only child.This is what Zahavi is talking about.No matter how much its mother has invested in it, it should still value its own life more than its mother, because its mother has only half of its genes.Even if the blackmailer is not an only child, and the siblings living with him are vulnerable young children, this strategy may not be beneficial, because the blackmailer has 50 percent of each threatened brother or sister. Genetic bets, and at the same time have a 100% bet on yourself.This strategy might have worked, I thought, if the all-you-can-eat predator had simply been used to snatching the largest chick from the nest.In such cases, it may pay for the smaller chick to go rogue and threaten to call in the predator, since the risk to itself is not too great. It would have been more plausible that the fledgling cuckoo would have benefited from this blackmailing tactic.As we all know, the female cuckoo lays her eggs in several nests of foster moths (foster), one in each nest, so that the young cuckoos can be raised by kept-in-the-dark foster parents belonging to completely different species.Thus, a cuckoo chick has no genetic stake in its siblings (for some insidious motive, a cuckoo chick of some species kills all of its siblings. We will see below Speaking of this case. Let me assume for the moment that we are dealing with cuckoo species that are able to live with siblings).If the baby cuckoo sings loudly and attracts predators, it may lose its own life, but the loss of the adoptive mother is even greater, perhaps the four biological children.Therefore, it pays for the foster mother to feed her more than her share, and the benefits to the young cuckoo may outweigh the risks. At some point, we should return to formal genetic language, lest we be confused by too many subjective metaphors.It is wise to do so.We say baby cuckoo yells predator, predator, come and eat me and all my little siblings in order to blackmail its adoptive parents!What exactly does this assumption imply?Let's use the formal language of genes for the moment. Genes that make cuckoos yell are increasingly abundant in the gene pool, because yelling increases the odds that foster parents will feed their young.The reason for the positive response of the adoptive parents to the yelling is that the genes that promote the response to the yelling have spread through the gene pool of the species that adopted the borerfly.As for the reason for the spread of this gene, individual adoptive parents lost more and more biological children because they did not feed the cuckoo extra food, while the adoptive parents who were willing to feed the cuckoo extra food lost their biological children. The offspring have much less chance, because the cuckoo's call attracts predators.Although genes that don't make cuckoos cry out are less likely to be eaten by predators than genes that make them cry out, cuckoos that don't call out suffer from the lack of extra food. Greater loss.As a result, the genes for yelling were allowed to spread through the gene pool. According to the more subjective argument above, we can make a series of similar genetic reasoning.This reasoning suggests that, while we can imagine that such a blackmailing gene might be able to spread through the cuckoo gene pool, it might not be able to spread through the gene pool of an ordinary species, at least not because it attracted spread by predators.In a common species, of course, genes that promote yelling may spread for other reasons, as we have seen above, and these genes may occasionally have the effect of attracting predators by chance. .For that matter, though, this selective influence of predation tends, if it has any effect at all, to tend to lessen the cry.In our hypothetical cuckoo example, the actual effect of the predator ended up making the cuckoo cry louder.At first glance, this may sound like a paradox, but it is. There is no evidence that cuckoos or other birds with similar brood-parasitic habits actually employ this blackmail tactic.But there is no doubt that they are ruthless.For example, some honeyguides, like cuckoos, lay eggs in the nests of other species.The newborn honeydew is born with a pair of sharp hooked beaks. When it comes out of the shell, although its eyes have not yet opened, its body is bald and hairless, and it has no one to rely on, it will take all its brothers and sisters. They were all pecked to death.Because the dead brother will not compete with it for food!The familiar British cuckoo uses a slightly different method, but the same result with the same result.Its incubation period is shorter, so it always hatches earlier than its milk siblings, and as soon as it hatches it throws the other eggs out of the nest, a mindless, mechanical, but destructive action. The consequences are unquestionable.It first squats under an egg, supports the egg with the concave part of its back, then retreats step by step to the edge of the nest, and at the same time keeps the egg balanced with its two wing bases until the top of the egg is turned out of the nest ,He fell to the ground.Then it disposed of all the remaining eggs in the same way.Since then, it can monopolize the bird's nest, and its adoptive parents can concentrate on taking care of it. One of the most notable facts I have learned in the past year is that of F. Alvarez, Arias.De.Reports from Spain by L. Arias de Reyna and H. Segura.They studied the ability of potential foster-parent birds, victims of cuckoo fooling, to spot intruders such as cuckoo eggs or newborn cuckoos.During their experiments, they placed cuckoo eggs and chicks in magpie nests, and for comparison, they also placed eggs and chicks of other species, such as swallows, in magpie nests.Once, they put a baby swallow into a magpie's nest.The next day, they found a magpie egg on the ground under the magpie's nest.The egg didn't break, so they picked it up and put it back in the nest for further observation.What a wonderful sight they saw!The suckling swallow behaved exactly like the cuckoo, throwing the magpie eggs out of the nest.They picked up the egg and put it in the nest again, with exactly the same result, and the baby swallow threw it out again.Like the cuckoo, it balances the magpie egg with the bases of its wings, holds it on its back, and then backs up, pushing the egg against the edge of the nest and letting it tumble outside. Alvarez and his collaborators are probably wise not to try to account for this startling sight.How did this behavior develop in the swallow's gene pool?It must correspond to something in the swallow's daily life.Milk swallows usually don't appear in magpie nests.Under normal circumstances, they never visit other birds' nests except their own.Does this behavior reflect an evolutionary adaptation against cuckoos?Could natural selection favor a counter-attack strategy in the swallow gene pool, the genes that favor fighting cuckoos with cuckoo weapons?It also seems to be true that parasitic cuckoos do not usually occur in swallows' nests.Maybe the truth is here.According to this theory, magpie eggs may have unexpectedly received the same treatment in the experiment because they, like cuckoo eggs, were larger than swallow eggs.If baby swallows can distinguish between large eggs and normal swallow eggs, it goes without saying that its mother also has this ability to distinguish.In this case, why is it not the baby swallow's mother who threw the cuckoo egg away but the baby swallow itself, which is much weaker in strength?有一種理論認為乳燕具有把臭蛋或其他碎屑從鳥巢裡消除掉的正常活動能力，但這種理論同樣是站不住腳的。因為老燕子能更好地完成這些任務，事實上也正是如此。既然有人曾經目睹孤弱的乳燕熟練地完成這種複雜的摔蛋動作，而同時成年燕子肯定能毫不費力地完成同樣的任務，因此這種情況迫使我得出如下的結論：從老燕子的觀點來看，乳燕是存心不良的。 我認為，真正的答案可能與布谷鳥毫不相干，這是可以想像得到的。乳燕是不是這樣對待它的同胞兄弟或姐妹的？這種景象確實令人毛骨悚然。由於最先出殼的乳燕必須和它的尚未出生的弟妹爭奪親代投資，因此它一出生就摔掉其他的蛋是合算的。 拉克關於每窩孵卵多少的理論，是從親代的觀點來考慮其最適量的。如果我是一隻燕子媽媽，在我看來，每窩最適量比如說是孵五隻蛋；但如果我是一隻乳燕，那我就會認為小於五的數目才是最合適的，只要我是其中一個就行！老燕子擁有一定數量的親代投資，它希望在五隻乳燕中平均分配。但每一隻乳燕都想得到超過五分之一的份額。和布谷鳥不一樣，它並不想獨吞全部投資。因為它和其他的四隻乳燕都有親緣關係。但它確實很想分到多於五分之一的份額。它只要能摔掉一隻蛋，它就能分到四分之一。再摔掉一隻就能分到三分之一。用基因語言來說，操縱殺兄弟姐妹行為的基因在基因庫中是會擴散開來的，因為它有百分之一百的機會存在於表現這種行為的個體內，而存在於它的受害者體內的機會只有百分之五十。 人們反對這個理論的主要理由是：如果情況果真是這樣，那很難使人相信竟會至今還沒有人見過這種窮凶極惡的行為。我對此沒法提出一個令人信服的解釋。世界上不同的地方有不同種類的燕子。我們知道，譬如說，西班牙種的燕子在某些方面不同於英國種的燕子，不過人們對西班牙種的燕子還沒有像對英國種的燕子那樣，進行過非常仔細的觀察。我認為，這種把兄弟或姐妹置於死地而後快的行為是可能發生的，不過沒有受到注意罷了。 我之所以在這裡提出燕子殺兄弟姐妹這種罕見行為的假設，是因為我想說明一個帶有普遍意義的問題。就是說，小布谷鳥的殘酷行為只不過是一個極端例子，用以說明任何一隻鳥巢裡都會發生這種情況。同胞兄弟之間的關係比一隻小布谷鳥同它的同奶兄弟的關係密切得多，但這種區別僅僅是程度問題。即使我們覺得動物之間的關係竟然會發展到不惜對親兄弟姐妹下毒手這種程度有點難以置信，但情況沒有如此嚴重的自私行為的例子卻是很多的。這些例子說明，一個幼兒從其自私行為中得到的好處可以超過它因損害到它的兄弟姐妹的利益而蒙受的損失兩倍有餘。在這種情況下，正如斷乳時間的例子一樣，親代與子代之間便會發生真正的衝突。 在這種世代的爭鬥中，誰將是勝利者呢？亞歷山大（R．D．Alexander）寫過一篇有趣的論文，他認為這樣的問題只能有一個總的答案。按他的說法，親代總歸佔上風。如果情況果真是這樣，那你閱讀這一章就算是白費勁了。如果亞歷山大是正確的，那就要引起很多有趣的問題。例如，利他行為之所以能進化，並不是因為有利於該個體本身的基因，而僅僅是有利於親代的基因。以亞歷山大的話來說，親代操縱變成了利他行為的另外一個進化的因素，它和直接的近親選擇無關。為此，我們有必要研究一下亞歷山大的推理過程，並使我們自己相信，我們是真的懂得他究竟錯在哪兒。為了證明他的謬誤，我們實在應該用數學演算的方法，但本書中，我們一直避免明顯地使用數理，而且事實上通過直覺的理解也能看出亞歷山大這篇論文的破綻所在。 他的基本的遺傳論點包括在下面這段經過刪節的引語裡：假定一個青少年個體使得親代利益的分配對自己有利，從而減少了它母親自身的全面繁殖能力。通過這個方式提高處在青少年時代的個體的健康水平的基因，肯定會在該個體成年時更大程度地降低其健康水平，因為這種突變型基因將越來越多地存在於這個突變型個體的後代體內。亞歷山大所說的是一個新近發生突變的基因，這個事實並不是這個論點的關鍵所在。我們最好還是設想一個從雙親一方繼承的稀有基因。在這裡，健康水平具有一種特殊的學術意義成功地繁殖後代的能力。亞歷山大的基本論點可以歸納如下：一個基因在促使其幼年個體搜取額外的食物時確實能增加該個體的存活機會，儘管其親代養育後代的總能力會因此受到影響。但當這個個體自己成為父母時就要付出代價。因為其子女往往繼承了同樣的自私基因，從而影響這個個體養育後代的總能力。這可以說是一種既損人又不利己的行為。這樣的基因只能以失敗告終，因此親代必定永遠在這種衝突中取得勝利。 這個論點理應立即引起我們的懷疑，因為作為論據的假設，即遺傳學上的不對稱性，事實上並不存在。亞歷山大使用親代與子代這樣的字眼時好像它們之間存在著根本的遺傳學上的不同。我們在上面已經談過，儘管親代與子代之間存在實際上的差異，如父母的年齡總比子女大、子女為父母所生等，但兩代之間並不存在根本的遺傳學上的不對稱現象。不管你從哪一個角度看，親緣關係都是百分之五十。為了闡明我的論點，我想重複一下亞歷山大的原話，但把親代、青少年以及其他有關字眼顛倒過來使用。假定一個親代個體有這樣一個基因，它使親代利益得以平均分配。通過這種方式提高作為親代個體的健康水平的基因，肯定在這個個體還處於青少年時代時更大程度地降低過它的健康水平。這樣，我們就得出和亞歷山大完全相反的結論，即在任何親代／子代的爭鬥中，子女必然會勝利！ 這裡顯然存在某種錯誤。這兩種論點的提法都過於簡單。我之所以要把亞歷山大的說法顛倒過來，並不是為了證明和亞歷山大相反的論點是正確的。我的目的在於表明，我們不能以這種人為的不對稱性作為論據。亞歷山大的論點以及我把它顛倒過來的說法都是由於站在個體的觀點上看問題而背離真理。亞歷山大是從親代的觀點看問題，而我是從子代的觀點看問題。我認為當我們使用健康水平這個技術性的字眼時，很容易造成錯誤。我在本書中一直避免使用這個字眼就是為了這個緣故。只有站在一個實體的觀點上看進化現象才是正確的，這個實體就是自私的基因。青少年個體的基因如有勝過親代個體的能力就被選擇；反之，親代個體的基因如有勝過青少年個體的能力就被選擇。同樣是這些基因，它們先後存在於青少年個體及親代個體之內，這並無自相矛盾之處。基因之被選擇是因為它們能夠發揮它們具備的力量：它們將利用可以利用的一切機會。因此，同一個基因，當它存在於青少年個體之內時，它可以利用的機會將不同於它存在於親代個體之內的時候。因此，在它的個體生命史中，兩個階段的最優策略是不同的。亞歷山大認為，後一階段的策略必然勝過前一階段的策略，這樣的看法是毫無根據的。 我們可以通過另外一個方式駁斥亞歷山大的論點。他心照不宣地在親代／子代關係與兄弟／姐妹關係之間假定一種虛妄的不對稱性。你應當記得，根據特里弗斯的說法，一個自私的幼兒在攫取額外的食物時必須承擔喪失其兄弟或姐妹的風險，而這些兄弟或姐妹體內部有它的一半的基因。正因為如此，它在攫取食物時會適可而止。但兄弟或姐妹只是各種親屬中其親緣關係指數是百分之五十的一類親屬。對一個自私幼兒來說，它自己的未來的子女和它自己的兄弟或姐妹同樣可貴。因此，它在攫取額外資源時應估算一下為此必須付出的全部代價，不能漫無節制；這種自私行為不僅使它喪失現存的兄弟或姐妹，而且要使它喪失其未來的子女，因為這些子女必然也會以自私行為彼此相待。亞歷山大認為，青少年時期的自私性遺傳到子女一代從而減少自己的長期繁殖能力是不利的，這一論點是言之成理的。但這僅僅意味著，我們必須將這種不利因素作為一項代價加在方程式裡。對一個幼體來說，只要它從自私行為中得到的淨利益至少不小於它的近親因此受到的淨損失的一半，那麼，這種自私行為還是合算的。但近親應該包括的不僅僅是兄弟或姐妹，而且應該包括它自己的未來的子女。一個個體應該把自己的利益看作是比它的兄弟的利益可貴一倍，這就是特里弗斯所作的基本假設。但它同時應該把自己看作是比自己的未來子女當中一個可貴一倍。亞歷山大認為，在利害衝突中親代享有天然的有利條件，他的這一結論是謬誤的。 除了他這個基本的遺傳論點外，亞歷山大還有一些比較切合實際的論點。這些論點來源於親代／子代關係中不可否認的不對稱性。親代個體是採取積極行動的一方，它實際上從事於尋找食物等工作，因此能夠發號施令。如果做父母的決定不再供養其子女，子女是沒有什麼辦法的，因為它們幼小，無力還擊。做父母的因此能夠無視子女的願望而要求子女絕對服從。這個論點顯然並不錯誤，因為在這種情況下，它所假設的不對稱性是真實的。父母當然比子女大些，強壯些，而且更老於世故。好牌看來都在父母手中。但子女手中也有一兩張王牌。譬如說，父母應該知道它們的每個子女到底餓到什麼程度，以便在分配食物時有所輕重緩急，這點很重要。它們當然可以搞平均主義，以完全相等的口糧分給每一個子女。但在最理想的環境裡，把略多一些的食物分給事實上最能充分利用這份口糧的孩子是能夠收到較大效果的。要是每個孩子能夠自己告訴父母它有多餓，對父母來說倒是個理想的制度。我們在上面已經談過，這樣的制度似乎已經形成。但子女說謊的可能性很大，因為它們確切知道它們自己有多餓，而它們的父母最多只能猜測它們是否老實。做父母的很難拆穿小小的謊言，儘管彌天大謊或許瞞不過父母的眼睛。 另一方面，做父母的最好能夠知道孩子什麼時候高興，孩子如果在高興的時候能夠告訴父母就好了。某些信號，如咕嚕咕嚕的叫聲和眉開眼笑，可能被選擇，因為這種信號使父母知道它們怎樣做才能為子女帶來最大的好處。看見子女眉開眼笑或聽見子女發出得意的叫聲是對父母的最大安慰，正像食物到肚對一隻迷路的老鼠同樣是莫大的安慰一樣。可是，正是由於甜蜜的笑臉和滿意的叫聲總會帶來好處，孩子就能夠利用笑臉或叫聲來操縱父母，使自己獲取額外的親代投資。 因此，在世代之間的爭鬥中，到底哪一方有更大的可能取勝是沒有一個總的答案的。最終的結局往往是子代企求的理想條件與親代企求的理想條件之間的某種妥協。這種爭鬥同布谷鳥與養父母之間的爭鬥相似，儘管實際上爭鬥不致於那麼激烈可怕，因為雙方都有某些共同的遺傳利益雙方只是在某種程度內或在某種敏感的時節裡成為敵人。無論如何，布谷鳥慣用的策略，如欺騙、利用等，有許多也可能為其同奶兄弟或姐妹所使用，不過它們不致於走得太遠，做出布谷鳥那種極端自私的行為。 這一章以及下面一章（我們將討論配偶之間的衝突）所討論的內容似乎是有點可怕的諷刺意味的。身為人類父母的人彼此真誠相待，對子女又是如此無微不至地關懷，因此這兩章甚至可能為天下父母帶來難言的苦衷。在這裡，我必須再次聲明，我所說的一切並不牽涉到有意識的動機。沒有人認為子女因為體內有自私的基因而故意地、有意識地欺騙父母。同時我必須重申，當我說一個幼兒應該利用一切機會進行哄騙說謊、欺詐、利用的時候，我之所謂應該具有特殊的含義。我並不認為這種行為是符合道德準則的，是可取的。我只是想說明，自然選擇往往有利於表現這種行為的幼兒，因此，當我們觀察野生種群的時候，我們不要因為看到家屬之間的欺騙和自私行為而感到意外。幼兒應該欺騙這樣的提法意味著，促使幼兒進行欺騙的基因在基因庫裡處於有利地位。如果其中有什麼寓意深刻的地方可供人類借鑒，那就是我們必須把利他主義的美德灌輸到我們子女的頭腦中去，因為我們不能指望他們或她們的本性裡有利他主義的成分。