Not by Coincidence…
Paley was right about one thing.Complex machines like watches and eyes are extremely improbable arrangements of matter.To claim that they could have come into existence in one single cosmic coincidence would be ludicrous.That would be about as likely as a hurricane blowing through a junkyard and assembling a Boeing 747 out of the scrap metal.
Natura non facit saltum (nature does not make leaps.自然界并不进行突变式发展)
But Paley was wrong in thinking that the only alternative to such a ludicrous scenario was that eyes and other adaptations had been desingned by God.Darwin’s theory of natural selection provides another alternative.Darwin argued that complex machines like the eye could evolve by a completely natural process,without the aid of any super-naural being.
Improvement by accident
This is how evolutionary biology explains the evolution of complex desings like the eye.Adaptations do not come about all in one go,by a single large mutation,but evolve gradually by accumulation hundreds of very small mutations.The mutations occur at random,with no plan in mind.
The evolution of the eye
In the case of the eye,for example,the first small change was probaly a slight increase in the sensitivity to light of a small piece of skin.All skin is slightly sensitive to light anyway,and it is not difficult to imagine that the offspring of one of our eyeless ancestors happened to be born with a bit of skin slightly more sensitive to light than normal.This was just an acident,of course.
It also just happened that this particular accident was a lucky accident,because it allowed the mutant baby to detect the shadow of a predator more quickly,and thus escape faster than its eyeless parents and siblings could do.
Of course,there were many other accidents that weren’t quite so lucky—many other mutant babies whose unusual features were disadvantageous rather than beneficial.These mutants did not have any offspring.
But the lucky mutant was more successful and had lots of offspring.Moreover,it passed the new gene for light-sensitive skin-bits on to its offspring,so the new gene spread through the population and eventually everyone had the light-sensitive skin patches.Later on,there were other mutations,some of which were also beneficial.The light-sensitive skin patches became light-sensitive concave dips,which were then filled in with transparent fluid and finally covered over with a lens.The eye had evolved by a process of natural selection.
The blind watchmaker
Natural selection,then,builds adaptations by accumulating many small accidental changes.The British biologist Richard Dawkins has compared natural selection to a “blind watchmaker”.It is a watchmaker because it produces complex desingns,but it is blind because it doesn’t produce these designs by conscious foresight,but simply by accumulating a series of random accidents.
This concludes our brief survey of evolutionary biology.Now it is time to fit the two pieces of the jigsaw puzzle together.
Fitting the pieces of the jigsaw puzzle together
Evolutionary psychology is the combination of cognitive psychology and evolutionary biology.But why should we combine these two sciences?What have they got to do with each other?The answer is simple.
Cognitive psychology tells us that the mind exhibits a very complex design.Evolutionary biology tells us that complax designs in mature can only come about by natural selection.Therefore,the design of the mind must have evolved by a process of natural selection.What is meant by saying that the mind is a “complex design”? Just how complex is the mind?
When cognitive psychologists first began to investigate the mind,they thought that it would be a very simple kind of program.
We thought that it would be an abstract,general-purpose problem-solver.All that the mental software required was a few general procedures that could be applied to any information.
When they set out to test this hypothesis,however,the cognitive psychologists found that they were wrong.They wrote some very simple programs that could sovle very abstract problems,but they found that these programs were unable to do many of the things that humans do easily.
Learning a language
One of these things that humans do easily is learning a language.In the late 1950s,the American linguist Noam Chomsky showed that a general-purpose learning program simply could not learn a language under the same conditions as normal human children.
In order for children to learn a language,they must first hear adults speaking it.But adult speech contans lots of errors,and no indication of what is correct and incorrect.
The technical term for this faulty data is “the poverty of the stimulus”.Learning a language based on this information alone would be like trying to figure out the rules of chess just by observing a few chess games in which some of the moves were illegal (but without knowing which moves were illegal).This would be impossible unless you already knew what information to look for.
So the only program that could learn a human language is a specific one that has been pre-programmed with specific information relevant just to language learning.Chomsky concluded that there is an innate “language accquisition device”(LAD) in the mind which knows what kinds of rules human languages can have.Human languages have a limited number of structures,which are collectively known as “Universal Grammar”.
When a child learns its first language,he or she doesn’t start from scratch.They simply select from their innate knowleged of universal grammer the rules that they hear being used around them.
In sense,language isn’t something that is learned;it is more appropriate to say that it just develops naturally,like a biological organ or an instinct.
Chomsky’s pioneering work on language was followed by similar discoveries in other areas of psychology.David Marr showed how another apparently simple task-seeing-was also very complex.Writing a program that could enable a robot to recognize even simple objects proved incredibly difficult.
So I found that vision required special software for seeing,with specific rules for detecting edges,motion,colour and depth.
David Marr’s theory of vision:We reconstruct three-dimensional images by building them up from simpler shapes like cylinders. (Hand-forearm-arm-human)
Cognitive psychologists began to realize that the mind was far more complex than they had first imagined.In 1983,the American philosopher and psychologist Jerry Fodor reached a stunning conclusion.
The mind could not possibly be a single,general-purpose program.Instead,it has to be a collection of many special-purpose programs,each with its own rules.
Fodor called these special-purpose program“modules”.
The modular theory of mind is still quite new,and is not yet accepted by all cognitive psychologists,but it is becoming more influential.Although it is very new idea,in a way it is also a return to a very old idea.For hundreds of years,people have divided the mind into“faculties”.In the 19th century,Franz Joseph Gall divided the mind into dozens of distinct capacities.
Just as the older universities were divided into different “faculties”…
Faculty psychology was largely abandoned at the beginning of the 20th century,but now,with the modular theory of mind,it is regaining prominence.
John Tooby and Leda Cosmides,two American psychologists who have pioneered many developments in evolutionary psychology,argue that there are hundreds,perhaps even thousands,of these special-purpose modules in the human mind.
We compare the mind to a Swiss-Army knife with lots of different gadgets.Each one is designed for a specific task.
This view is sometimes called the “massive modularity”thesis to distinguish it from a more limited view of modularity.
When Fodor proposed a return to the tradition of “faculty psychology”in his 1983 book,The Modularity of Mind,he didn’t envisage hundreds of modules.He proposed that there were only a few of them.There were modules for processing sensory input(vision,sound,taste,touch,smell and language),but no more.Fodor claimed that these “input processes”fed information into general-purpose programs called “central processes”.The central processes were not modular in Fodor’s account.Fodor thinks evolutionary psychology has gone too far.
No Central Processes
Evolutionary psychologists are opposed to Fodor’s idea of “general-purpose central processes”for the same reason as they are opposed to the idea that the whole mind is a general-purpose program.
General-purpose problem solvers don’t work because there are no “general problems”,only specific ones.
If this input systems are modular,why not the central processes too?
Modules and Adaptations
A modular mind is clearly far more complex than a single general-purpose program.It has lots of interlocking parts that function smoothly together to process information.It has an innate structure that develops naturally,like a biological organ.According to evolutionary biology,these characteristics occur only as a result of natural selection.
We can therefore ask how the different bits of the mind evolved.Evolutionary psychology is the research program that attempts to answer this question.
Adaptations and environments
According to evolutionary psychology,the various mental modules are adaptations designed by natural selection.Every adaptation is designed to solve an adaptive problem.An adaptive problem is something that an organism needs to solve in order to survive and reproduce.
For example,one important adaptive problem faced by many animals is the problem of staying warm.Some animals solve this problem by developing coats of fur.Others solve it by thick layers of blubber.
Different environments pose different adaptive problems and so require different adaptations.There is not much point in having eyes if you live deep underground,where there is no light.If you want to understand any adaptation,therefore,you must know something about the envrionment in which in evolved.
What was the environment in which the various modules in the human mind evolved?This is a tricky question,because the modules did not all evolve at the same time,so they did not all evolve in the same envrionment.
Some modules evolved relatively recently,after the human species split from that of our closest relative,the chimpanzee.These modules are unique to humans.
Shared and Unique Modules
Other modules evolved a long time ago,when the commom ancestor of humans and reptiles was alive.These modules are not unique to humans.There are similar modules in the minds of reptiles.This does not mean that we have a “reptilian”bit in our mind,however.Mental modules,like all adaptations,do not stop evolving once they have appeared.They keep changing along with the environment.So,for example,both humans and crocodiles have eyes because they are descended from the same ancestral species in which eyes first evolved.But this does not mean that humans have reptilian eyes.
Human and crocodiles have slightly different kinds of eye.Because our eyes have evolved in different ways since the human lineage diverged from the reptilian lineage.
If we want to investigate the most distinctively human modules,the ones we don’t share with any other animals,we will have to look at the environment in which our ancestors lived after the human lineage split from that of the chimpanzee.
Out of Africa
Around 100,000 years ago,some of our ancestors began to emigrate out of Africa,and eventurally colonized the whole world.But 100,000 years is only about 5,000 generations—too short a time for evolution to produce any major changes.Human haven’t changed much in that time,so we can ignore it when discussing the evolutin of the mind.This means that all the history of human civilization and culture,from the birth of agriculture some 10,000 years ago until the present,is irrelevant to understanding the design of the human mind.
Our minds did not evolve in a world of cities and cars,nor even in a world of ploughs and farming.We are all “stone-agers living in the fast lane”.
The Social Environment
What was life like on the African savannahs?The climate was hot and sunny,and the flat plains were covered in long grass dotted with trees,some of which were rich in high-quality food like fruit and nuts.This was the physical environment in which the human mind evolved.However,when we are considering the evolution of the human mind,it is just as important—perhaps even more important—to consider the social envrionment.
The social environment refers to the orther minds around you.
Like most primates,our ancestors lived in tightly-knit groups with a complex social structure.Interacting with the other people in the group was just as important for their survival as bing able to detect and escape from predators.
Now that we know a little bit about the environment in which our most recent ancestors lived,we can ask what adaptive problems they faced.When we know what adaptive problems they faced,we can make some educated guesses about the kinds of mental adaptations(mental modules)that natural selection might have produced to solve them.Then,as with any other scinece,we can try to find evidence to see whether these guesses are right or wrong.
So what were the adaptive problems faced by our hominid ancestors?Various considerations drawn from biology,primatology, archaeology and anthropology suggest what the most important adaptive problems would have been.
Avoiding predators—eating the right food—forming alliances and friendships—providing help to children and other relatives—
Reading other people’s minds—communicating with other people—selecting mates.
All of these things are crucial for passing on your genes.So we should expect natural selection to have designed mental modules that enabled our ancestors to achieve these objectives in the ancestral envrionment.In the next part of this book we will examine these modules in more detial,beginning with predator avoidance.
Avoiding predators is a very important problem from the genes’ point of view.Genes cannot get themeselves passed on to the next generation if their owner is eaten.Any genes that tend to make their owners avoid predators will therefore spread throughout the population.
But genes do not cause behaviour directly.Rather,they help to build mental modules,and the mental modules cause behaviour. Gense for predator-avoidance work by building a predator-avoidance module.
What would a predator-avoidance module look like?It would have to be able to detect possible predators,distinguish those that were real dangers from those that weren’t,and—in the case of real danger—trigger avoidant or defensive behavious.
In fact,each of these tasks might be carried out by a separate module.So the task of predator-avoidance might be subserved by a group of modules rather than a single module.
The first module in the predator-avoidance system would detect possible predators.With any detection system,however,there is a trade-off between accuracy and speed.Think of a burglar alarm.On the one hand,you want the alarm to be accurate—you don’t want it to be triggered by stray cats.You don’t want false alarms.On the other hand,you also want an alarm that goes off immediately a burglar attempts to break in.It’s not much use having a burgalr alarm that rings five minutes after the burglar has left the house.
The problem is that it takes time to figure out whether the animal entering the house is a burglar or a cat.
The more accurate the alarm is,the slower it is.Conversely,if you want a faster alarm,you will have to put up with a higher rate of false alarms.
Which is more costly—a false alarm or a slow detector?If it is a question of detecing predators,a false alarm causes you to waste energy by running away from something that is not in fact a danger.A slow detector,however,can cause you to be eaten.So it is better to have a fast system that occasinonally gives false alarms than a slow system that is always accurate.So we should expect the predator-detection module to be fast and inaccurate rahter than slow and precise.
While you are reacting to the alarm given off by the predator-detection module,another module can then take a bit more time to decide whether of not the alarm was triggered by a genuine danger.If it was,then the avoidance behaviours are maintained.If the second module decides that the first module gave a false alarm,however,it can override the avoidance behaviour.
Two Neural Pathways
There is some evidence that this is in fact the case.The American neuroscientist Joseph LeDoux has shown that the emotion of fear—which prepares us to flee from predators or freeze to avoid being seen—is subserved by two neural mechanisms.One “fast and dirty”mechanism is,as the name suggests,very quick but not very accurate.It often gives false alarms.The other mechanism is much more accurate but slower.
For example,suppose you are walking in the jungle.You look down and see a long,thin object.You freeze,because the fast and dirty mechanism thinks it’s a snake.Then,milliseconds later,you relax,because the slower,more accurate mechanism realizes that the object is in fact a stick.Having both of these machanisms is a bonus.
The fast and dirty mechanism gets you out of trouble quickly but gives off some false alarms.The slow and clean mechanism tells you when the alarms are false,and so stops you wasting too much energy in reacting to them.Sometimes the slow and clean mechanism doesn’t kick in,and we continue reacting to false alarms.This may be what happens in some phobias.
Food Preference Modules
Avoiding predators is vital for survival,but so is consuming the right food.Of all the potentially edible things around you,some are very nutritious,some are poisonous,and some are neither.
Genes that predisposed their owners to consume nutritious food and avoid poisonous food would spread through the population. As with predator-avoidance,however,genes do not cause this behaviour directly.They build mental mechanisms that lead us to desire some foods and dislike others.
Fat and Sugar
Animal fat and sugar are highly nutritious,but they were relatively scarce in the African savannah where our ancestors lived.To get animal fat it was necessary to kill an animal or scavenge one that had already been killed.To get sugar it was necessary to find ripe fruit.Both of these were complicated—and something dangerous—tasks.In a situation like this,it would have been highly adaptive to have strong desires for fat and sugar.
Those who have such strong desires will be more likely to seek out fat and sugar.Despite the attendant difficulties and dangers.
On balance,they would tend to consume more of these nutritious foods,and so they would be more likely to pass on their genes—including their genes for liking fat and sugar.
Fat and sugar are bad for you if you eat too much of them,but in ancestral envrionments these resources were scarce,so there wasn’t much chance of consuming too much.Today,however,we have supermarkets and fast-food resaurants to cater for our evolved tastes.Fat and sugar are no longer difficult to find.
We were desinged to live in such a different envrionment,and this “envrionmental mismatch”is the source of many current problems.
Eating the right food does not just involve seeking out nutritious food.It is also important to avoid poisonous food.Just as natural selection has desingned modules that make us prefer fat and sugar,so it has also designed modules that make us avoid eating rotting flesh and faeces.
These poison-detector modules work by means of the emotion of disgust.
In other words,when the module detects a food that it thinks is poisonous,it activates the feeling of disgust,and it is this feeling—not any conscious deliberation—that makes us avoid the food.
The two adaptive problems we have just examined—avoing predators and eating the right food—are problems posed by the physical envrionment.Howver,as we have already seen,when considering the evolution of the mind,it is just as important to consider the problems posed by the social envrionment.
The social envrionment refers to the other conspecifics (animals of the same species)with whom you live.For many animals,the social envrionment is virtually non-existent,because they live solitary lives.
Toad:I live on my own.I only meet other toads when I want to mate.
Living in Groups
Primates are unusual in that they live in tightly-knit social groups with complex hierarchies and alliances.
Living in groups benefits primates because it provides extra defences against predators.
It is harder for a predator to catch an animal in a group than an isolated animal because groups have more eyes to detect predators,and because other group memebers can come to the aid of one who is being attacked.
Alliances and Coalitions
But group living poses adaptive problems for primates.With lots of other consepecifics around you,all with the same food preferences,competition becomes more intense.Squabbles for scarce resources become common.
The way we tend to solve this problem is by forming alliances between small numbers.Two or three of us form a coalition to provide mutual support against the other members of the group.
Increasing the Group
Our ancestors continued and extended this primate lifestyle.After the human lineage split from the chimpanzee lineage some six million years ago,the size of human groups began to increase.
The increase in group-size meant that forming alliances became even more important for survival.
For our ancestors,forming alliances and friendships was just as vital as eating the right food.Those who lacked the ability to form alliances and friendships were in as much danger as those who lacked the ability to detect predators.
But forming alliances is not an easy task.The main problem is the risk of defection.An alliance is an “I’ll help you if you help me”arrangement.It is all about exchanging favours—which biologists call “reciprocal altruism”.But there is a problem with any such arrangement.
There is always a risk that one of the members of the alliance may take the benefits without paying the costs. “I may accept favours from the other members of the alliance and never return them.”
This is known as the “free-rider”problem and it is the fundamental adaptive problem posed by group living.
The Free-Rider Problem
Those animals that cannot solve the free-rider problme cannot live in groups.To see why,imagine a group of animals that strikes up an alliance in which one of the members is a free-rider.Whenever the free-rider is in danger,or hungry,the other members of the alliance come to his aid.The other members pay a cost for helping the free-rider,by riking their lives for him or by giving him some of their precious food.The free-rider enjoys these benefits,but never pays the costs of returning the favours.
Undetected,the free-rider will obviously be more successufl at surviving and reproducing than the public-spirited suckers.So genes for free-riding will become more frequent in the gene pool.Eventually,everyone will be a free-rider.
But then,no one will be helping anyone else.Alliances will disintegrate and group-living will no longer be possible.S
The Evolution of Cooperation
All animals that live in groups have found ways of solving the free-rider problem.Different species solve the problem in different ways,but there are some fundamental conditions that any solution must meet.These conditions were worked out by an American political scientist called Robert Axelrod in the early 1980s.Axelrod showed that the free-rider problem can only be solved if the following three conditions are satisfied.
1. Organisms encounter the same organisms repeatedly.
2. Organisms can recognise those they have met before and distinguish them from strangers.
3. Organisms can remember how those they have met before have treated them on previous encounters.
“I discovered these three conditions by organizing a tournament in which different computer programs competed against each other.”
Why are Axelrod’s three conditions necessary for solving the free-rider problem?The answer has to do with punishment and reward.When these three conditions are satisfied,free-riders can be punished and cooperators can be rewarded.Free-riders who have refused to do return favours can be punished by refusing to do any more favours for them.Cooperators can be rewarded by continuing to help them when they need it.
The simple strategy is called “tit-for-tat”.When a group of organisms interact on the basis of tit-for-tat,free-riders no longer have the advantage.Cooperation can evolve and group cohesion can be maintained.
All three conditins for using tit-for-tat were present in our hominid ancestors.In the small,tightly-knit groups of fifty to a hundred people in which they lived,the frist condition was easily satisfied.Day after day,we ineract with the same people.The second condition is satisfied by the evolution of sophisticated face-recognition module.The third condition is met by the evolution of a sophisticated memory of recording social interaction.
For each acquaintance,we keep a mental tally of how much they have done for us and how much we have done for them.If the tally shows that someone has consistently done less for us than we have done for them,then the next time they ask for help,we will be less inclined to give it.We punish free-riding by refusing to cooperate.
Cognitive Adaptations for Social Exchange
In order to keep a mental tally,we must have some way of woring out the value of the favours that others do for us.These must be some way of comparing this with the value of the favours that we do for others.
Leda Cosmides and John Tooby have argued that humans evolved special modules for calculating these things.They propose that these cognitive adaptations are the basis of all human behaviour involving exchange—from trading favours to trading stocks and shares.
The calculations performed by these “social accounting”modules must take into account a whole range of variables when working out the value of a favour.The value of a favour depends both on the cost to the donor and the benefit to the recipient.A favour that costs the donor a lot is worth more than a favour that costs the donor little.A favour that benefits the recipient a lot is worth more than a favour that benefits the recipient a little.The value of favour is the product of the cost to the donor and the benefit to the recipient.
The costs and benefits of any kind of favour are not fixed in advance,but depend on the context.
“—If you hand over your last piece of bread to a friend,this favour costs you a lot if you are on the verge of starvation.But it costs you little if you have just had a big meal.The same favour beniefits your friend a lot if he is on the verge of starvation.
—But doesn’t benefit me very much if I’ve just been to a banquet.”
The social accounting modules must consider all these details.
Modules for Helping Children and Other Relatives
All this talk about social accounting and tit-for-tat suggests that altruism and cooperation can only evolve on a strictly reciprocal basis.If this were true,no animal would ever help another animal unless there was a good chance of receiving an equally valuable favour in return.But this is clearly not the case.
Nature is full of examples of animals that provide help to other animals from whom they cannot expect any repayment.And humans are no exception.
Parenting is the most obvious example of such non-reciprocal altruism.In all species that care for their young,parents provide help that they never expect their offsping to repay.Humans provide more intensive and long-lasting care for their offspring than any other species,and this is entirely non-reciprocal.So there must be another element that enters into the social-cooperation modules besides the social accounting already described.What is it?
The example of parenting providing a clue to what this element is.When biologists examined the examples of non-reciprocal altruism in the animal kingdom,they noticed that they all had one feature in common.This kind of altruism is directed exclusively towards genetic relatives.In 1964,the British biologist William Hamiton came up with a theory to explain why this was the case.He argued that the fundamental unit of evolution was not the organism but the individual gene.
Close relatives share many genes,so genes which predispose their bearers to help close kin are in effect helping copies of themselves.A gene might be able to assist replicas of itself that are sitting in other bodies.If so,this would appear as individual altruism but it would be brought about by gene selfishness.
Non-reciprocal altruism at the level of the organism,such as the care that parents provide for their children,is the result of “selfishness”at the level of the gene.In 1975,the British biologist Richard Dawkins popularized Hamilton’s ideas in his famous book,The Selfish Gene.
How Related Are You?
Hamilton showed that non-reciprocal altruism could evolve whenever organism had some means of estimating their “degree of relatedness”to other organisms.The degree of relatedness is the chance that a randomly chosen gene in one organism will be shared by another organism as a result of common descent.The British geneticist Sewall Wright had already coined the symbol r in 1922 for this concept which he called the “coefficient of relatedness”.
“I calculated the following values for r.” :
Type of relative/examples/value of r
First-degree relatives/Parents,children,full siblings/50%
Second-degree relatives/Grandparents,grandchildren,half siblings,uncles,aunts,nephews,nieces/25%
Third-degree relatives/First cousins/12.5%
Hamilton showed that non-reciprocal altruism can evolve whenever there are mechanisms that ensure that the coefficient of relatedness will tend to exceed the cost-benefit ratio of the altruistic act.This can be written as the following equation.
“c”stands for the cost of the favour to the donor,and“b”stands for the benefit of the favour to the recipient.This is known as “Humilton’s rule”.
The Evolution of Nepotism
What mental mechanisms evolved to help our ancestors follow Hamilton’s rule?Clearly,they must have some mechanism for distinguishing kin from non-kin,and assessing the degree of relatedness—a kin-recognition module.This must have played a vital part in the system of modules governing the provision of favours and help to others.
Suppose the chance of being repaid were low or nil?Then the social-cooperation modules might consult the kin-recognition modules to see whether the potential beneficiary was a relative or not.If they were,then help could be provided without any expectation that it would be returned.
Alliances and cooperation would therefore have been more likely to develop between close relatives than between unrelated individuals.In other words,evolutionary psychology predicts that humans should have instinctual tendencies towards nepotism.
The Truth About Cinderella
In the 198os,two Canadian psychologists,Martin Daly and Moargo Wilson,set out to test this Darwinian prediction.In one study,they conpared the childcare provided by natural parents and by step-parents.Step-parents are in a very unusual situation from an evolutionary point of view.They are caring for a child tho they know is not their own.Even though they may care for the child conscientiously,evolutionary theory predicts that the childcare modules will not be activate in the same way was in biological parents.But is this true?
Looking for a way to compare the parental love shown by biologcila parents and step-parents,Daly and Wilson reasoned that,since love inhibits violence,those with greater love would show,on average,lower levles of violence.
Child abuse by step-parents is rare.But we predict that child abuse by biological parents will be even rarer.
When Daly and Wilson looked at statistics of child abuse in North America,they found a striking confirmation of the Darwinian prediction.In the USA,they found that a child living with one or more substiute parents was about 100 times as likely to be fatally abused as a child living with natural parents only.A similar pattern was observed in Canada,where statistics showed that, for children of two or younger,the risk of being killed by a step-parent was about 70 times that from a natural parent.These data provide strong support for the existence of childcare modules in humans that help parents to recognize their own children and to channel parental investment preferentially towards them.
Allocating Resources to Offspring
Another problem that parents face,besides that of distinguishing their own children from those of others,is the problem of resource allocation.Parents have limited time,energy and food,and they must decided how much of these precious resources to give to each of their children,and how much to use for their own survival.
Parents who allocate minimal resources to their children will survive for longer than more generous parents.But the children of the stingy parents will have less chance of surviving,and so less chance of passing on the parents’ genes.So it pays parents to be generous to their children.
On the other hand,parents who are so generous that they compromise their own survival risk dying and having no more offspring.There is a trade-off,then between parental generousity,which raise the survival chances of actual offspring,and parents withholding,which raises the survival chances of future offspring.
The Resource-Allocation Module
We should expect natural selection to have designed special mental machinery for calculating the optimal amount of resources to allocate to each child at any given moment.This resource-allocation module will have to take into account a number of decisive factors.
The age of the children.The health of the children.Sick children need more care unless they are so sick that it’s better to let them die.Older children are more capable of fending for themselves,and so need fewer resources to be provided by their parents.And hwo many more children you can reasonably expect to have in the future.
The problem of allocating resources to children is made mre complicated by the fact that the children themselves may disagree with their parents about how much they should be given.Children may want more than their parents are prepared to give.The evolutionary basis for this was set out by the American biologist Robert Trivers in 1974,in a famous paper on “Parent-Offspring Conflict”.
Trivers argued that the crux of the matter lies with the fact that a child is twice as related to itself as it is to its siblings.Everyone is 100% generically related to himself, but only 50% related to his brothers and sisters.
So,even though you care about your brothers and sisters,you care about yourself even more.From the parents’ point of view, though,things are somewhat different.Parents have the same degree of relatedness to all their children,and so value them all equally.This is the source of parent-offspring conflict.
How Much For Me?
To illustrate the problem,imagine a mother who wants to divide a cake between her two children.The children are equally realted to her,so, other things being equal,she should cut the cake in half.But now think of it from the point of view of each child.Each child has a genetic stake in the welfare of the other child.
Each child is 100% related to itself,but only 50% related to its sibling,so(other things being equal)each child should want twice as much cake for iteself as for its sibling.If the child chould divide the cake up,it should give a third to the sibling,and keep two thirds for itself.
This simplified example illustrates the general principle behind the evolutionary theory of parent-offspring confilct.The conficts arise because children always want slightly more than what their parents think is their “fair share”.Take weaning,for example. No child wants to breast-feed forever.
There comes a time when the benefit that a child derives from the mother’s milk is less than half the benefit that a younger sibling would gain from the same milk.
The Benefit of Weaning
So a pint does come when it is in the child’s genetic interest to seek alternative sources of nourishment,and let a younger sibling have the mother’s milk to itself.The problem is that this point in time is always later than the point at which the mother comes to the same conclusion.The mother wants to wean the child when the benefit it gains from breastfeeding is less than the benefit that a younger sibling would gian.
So the mother always wants to wean the child before the child wants to wean itself.
We have seen that the various modules for social exchange evolved to help our primate ancestors solve the free-rider problem.This enabled them to form the stable alliances that hold together the social groups in which all higher primates live.But the increasing size of these groups posed a problem in itself—a problem which was solved by learning how to “mind-read”.
Of course,we don’t read other people’s minds by direct telepathy.This is not what evolutionary psychologists mean by “mind-reading”.Mind-reading involves guessing what people are thinking on the basis of observing their actions and their words.
Group Size and Social Intelligence
The size of the groups in which our ancestors lived increased dramatically during the course of hominid evolution.Around six million years ago,when our ancestors resembled modern chimpanzees,the average group size was about 50.By three million years ago,our “australopithecine”ancestors were living in groups of about 70.A million years later,our “habline”(tool-making) ancestors were living in groups of about 80.The first true humans(Homo sapiens sapiens),who emerged around 150,000 years ago,probably lived in groups of around 150.
As groups got bigger,the problems posed by group living got more complex.Not only did our ancestors need bigger memories to keep track of the fast-changing pattern of alliances in the group,but they also needed more sophisticated social reasoning capacities to maintain a delicate balance between their conflicting loyalties.
In order to play the political games vital to survival in a larger group of primates,we have to become amateur psychologists.
This idea is known as the “Machiavellian intelligence”hypothesis,after Niccolo Machiavelli,the infamous Italian political theorist.Machiavelli’s book The Prince outlines some of the dirty tricks that successful politicians use obtain and maintain power.The Machiavellian intelligence hypothesis starts from the idea that these dirty tricks are not just the preserve of politicians.
“We all use them in our everyday life,as we help our friends and attempt to outsmart out enemies,make (and break)promises, and tell lies. ”
Even this“everyday politics”requires a fairly sophisticated understanding of human psychology—in particular,a special mental module for “reading other people’s minds”.
Theory of Mind
This “mind-reading modules”is usually referred to by evolutionary psychologists as the “Theory of Mind”module.This is because it seems to operate on the basis of a theory of how the human mind words.The theory that the module uses is, apparently,the very same theory that we find in “folk psychology”and in cognitive science—the “belief/desire”theory which states that actions are caused by mental processes like beliefs and desires.
In other words,folk psychology is not just a cultural invention.It is an innate part of the human mind.Adults do not teach children to understand human behaviour in terms of beliefs and desires.Rather,children instinctively develop the ability to do this,because they are genetically programmed to do so.
The Theory of Mind module develops during the first years of life,and is usually complet by the age of four-and-a-half.At that age,children can pass “false-belief tests”.
The Sally-Ann Test
A classic fale-belief test is the so-called “Sally-Ann”test.A psychologist introduces a child to two dolls called Sally and Ann.Then the child watches while Sally puts some sweets dunder a cushion and leaves the room.While Saly is out of the room, Ann takes the sweets from under the cushion and puts them in her pocket.When Sally comes back into the room,the psychologist questions the child.
“Where does Sally think the sweets are?” “In Ann’s pocket!”
Before the age of four-and-a-half,this is what children usually say.Lacking a fully-developed Theory of Mind,they cannot comprehend the notion that other people can hold beliefs that are different from their own.They assume that everyone believes what they believe.
Theory of Mind and Autism
After the age of four-and-a-half,children respond very differently to the Sally-Ann test.When asked where Sally thinks the sweets are,they now replay, “Under the cushion”.
They know the sweets are in Ann’s pockets,but they now have a fully-developed Theory of Mind,so they understand that beliefs that differ from their own.Then also understand that these beliefs can be false.Autism occurs when children fail to develop a properly functioning Theory of Mind module.
According to the British psychologist Simon Baron-Cohen,autistic people are “mindblind”.
Lying and Tactical Deception
Without a theory of Mind,it would be very difficult to play the political games necessary for living in human society.For one thing,it would be impossible to lie.
In order to lie,you must first understand that other people can hold different beliefs from yours.And those beliefs can be false.
Only then can you attempt to manipulate another person into holding a false belief.This is why children under the age of three cannot lie convincingly.
All animals that regularly interact with other memebers of their own species face the problem of communicating with each other.Different species solve this problem in different ways,but many use sounds because,unlike visual signals,sounds can be perceived at night and over long distances.All primates use their vocal cords to produce different kinds of signals to convey different kinds of information.Humans,however,have evolved the most sophisticated communication system in the animal kingdom—language.
Vervet monkey gives alarm calls to warn other vervets about snakes.Bees dance to tell other bees where the flowers are.
The Language Acquisition Device
Special mental machinery is required in order to learn and use a human language.We have already seen how Chomsky’s work in the 1950s and 60s showed that it would be impossible for children to learn a language as quickly as they do unless they were pre-programmed to do so.In other words,all children must be born with a special-purpose language-learning program,or Language Acquisition Device.
The Language Acquisition Deviec is unique to humans.
Some primatologists argue tha tchimpanzees also have the capacity to acquire language.But most linguists reject this view.Is that all he can say-ask for a banana?
Despite valliant attempts to teach them to use English and sign language,chimpanzees have never succeeded in learning more than a few dozen words and producing a few very simple sentences.Human children,on the other hand,learn thousands of words and master the most complex rules of grammer by the age of five.
The Evolution of language
No one knows when our ancestors acquired the ccapacity to use language,but it must have been before they moved out of Africa,some 100,000 years ago.After that time,different human groups became separated from each other for thousands of years.If the language modules evolved after the emigration from Africa,it would mean that exactly the same mental machinery had evolved independently in all the different human groups.This is extremely unlikely.
Anatomical studies suggest that the capacity to use language evolved between 300,000 and 200,000 years ago.It was then that the position of the larynx changed to its current position,which is much lower down than the larynx of other primates.The lower larynx of humans enables them to produce a muc wider range of sounds.The lower tracheal opening is also responsible for the human capacity for choking.Our ability to speak was only purchased at the price of an increased risk of asphyxiating on our food.
Why did our ancestors evolve such a sophisticated communication system?One theory is that it enabled them to hunt more effectively.According to this view,the primary function of language was to exchange information about the physical and ecologcial environment.In 1993,the British anthropologist,Robin Dunbar,challenged this theory.Dunbar suggested that the primary function of language was to exchange information about the social environment.
Reciprocal Altruism Again
Dunbar’s agument was based on the observation that,some time between 500,000 and 200,000 years ago,our ancestors began to live in much larger groups than before.Dunbar estimated that group size increased to about 150 individuals.We have already seen how primate groups are held together by networks of alliances formed by reciprocal altruism.
But for reciprocal alruism to work,you need informaiton about who you can trust and who you can’t.You need to be able to distinguish the cheats from the cooperators.
Chimps gain this information by direct personal interaction,especially grooming.They spend large amounts of time removing fleas and dirt from each other’s backs,and this mutual grooming is the social cement that holds their alliances together.Achimp in trouble is far more likely to receive help from a grooming partner than any other chimp.
Since reciprocal altruism depends on having direct interactions with others,there are limits to the size of the group that can be held together by this mechanism.There is a limit to the number of people you can meet and interact with on a regular enough basis to get information about how likely they are to cooperate.
Dunbar argued that language evolved to provide our ancestors with another way to get the valuable social information about who you can trust.Instead of discovering whether someone is a cheat the hard way—by being cheated—our ancestors were able to find this out by talking to other people.In Dunbar’s view,the first function of language was gossip.This might explain why humans are so fascinated by gossip about other people’s behaviour.
By facilitating the exchange of social information,language enabled humans to reap the rewards of living in larger groups. Reciprocal enalbed humans to reap the rewards of living in larger groups.Reciprocal altruism could hold these larger groups together because it no longer needed to be direct.
Direct reciprocity is when you give something to someone in the hope that they will return the favour later on. “I’ll scratch you back if you scratch mine.”Indirect reciprocity is when you give something to someone in the hope that someone elase will return the favour.It works because of a crucial thing-reputation.And this will cause others to be generous to you.
The importance of Reputation
If other poeople see or hear about your acts of generosity,and if other people tend to be generous to those with a good reputation,then it pays you to be generous.Even if the recipient of a favour never returns the favour directly,it will get you a good reputation.And this will ccause others to be generous to you.On the other hand,if you are not generous,you will acquire a reputation for stinginess.And others will punish you for this by being stingy to you.I won’t scratch your back if you don’t scratch others.
Most of the adaptive problems that we have discussed so far—avoiding predators,eating the right food,forming alliances,reading other people’s minds and communicating with other people—relate to the fundamental problem of survival. But while an organism’s survival is vitally important from the genes’ point of view,there is something even more important.
The most important thing of all is reproduction.This ensures that the genes are passed on to the next generation.An organism is just the genes’ way of making more copies of themselves.
From the gene’s point of view,the survival of the organism is merely a means to this end.If an organism lives for a hundred years,but has no offspring,this is no use to be the genes.
The Mating Game
Some species reproduce by diving into two parts,each of which becomes a separate individual.In these “asexual”species,there is no need to find a mate,since you can reproduce without one.Most species,however,reproduce sexually.This involves finding a mate and swapping genes with them.Biologists still disagree about why sex evolved.Most argue that sexual reproduction confers some advantage to the individual organism,but there is no consensus about what this advantage is.
Humans are a sexually-reproducing species.In order for us to reproduce,we must fist find a mate.
Finding a mate is not an easy task.First,you must choose a suitable candidate from among the many possible mates available.Second,you must persuade at least one of them to choose you.
We should expect natural selection to have designed special mental mechanisms that enabled our ancestors to solve the problems specific to choosing and obtaining a suitable mate.Selecting a suitable mate is very important because mates provide two things on which the survival of your offspring depends:genes and parental care.The survival chances of offspring depend on the quality of these two resources.We will now look ate each of them in more detail.
The Genes are in the Selection
The first way in which yourmate affects the survival chances of your offspring is by providing—or falling to provide—good genes.In a sexually-reproducing species,offspring inherit 50%of their genes from each parent.If you mate with someone who has bad genes(“bad”in the sense that they lower your chances of surving and reproducing),your offspring will probably inherit some of these bad genes.That will lower their chances of surviving and reproducing.
That will raise their chances of surviving and reproducing,and so raise the chances of your genes getting passed on to future generations.
The Importance of Looking Good
How did our ancestors solve the problem of selecting mates with good genes and avoiding those with bad genes?Obviously,we weren’t born with DNA testing-kits,so we evolved more indirect measures.Sensitivity to small differences in physical appearance is one such measure.Physical appearances provide important clues to the quality of one’s genes.
For example,the more symmetrical your body is,the better on average your genes are.This is because less robust genes are more likely to get knocked off course by environmental setbacks such as physical injuries and parasites.
If the left and right sides of the body are very similar,then the more likely it is that the genes are quite robust.
Anyone who was sensitive to small differences in bodily symmetry,and who preferred to mate with more symmetrical people, would tend to have children with better genes.So we would expect natural selection to have designed a mate-seleciton module that was geared to detect and prefer more symmerical mates.
What’s the Evidence for Symmetry?
Is there any evidence to show that humans do,in fact,prefer more symmetrical mates?There is.The psychologist Steve Gangestad and the biologist Randy Thornhill measured various features,from foot breadth and hand breath to ear length and ear breadth,and combined these measurements to produce an overall index of bodily symmetry for each person in their study.
“We then asked volunteers to evaluate these same people for attractiveness,and compared the results.We found that these was a close correlation between the attractiveness-rating and the degree of symmetry.”
More symmetry people were seen as more attractive.
The Biology of Beauty
Many people today think that standards of beauty are entirely cultural artefacts.But in the past few decades,evidence has increasingly emerged to show that there are many aesthetic preferences that are both universal and innate.Preferences for more symmetrical people,for example,are universal.
Another universal preference is the male preference for the classic “Hourglass”figure.
The psychologist Devendra Singh has found that while cultures vary in their view of he ideal weight for women,the ideal waist-hip ratio is always the same—people everywhere rate a waist-hip ratio of 0.7 as the most attractive.This is the classic “hourglass figure”.
The Fertility Factor
Why has natural selection endowed men with a preference for the hourglass figure?Because the waist-hip ratio is a good indicator of fertility.Women with a 0.7 waist-hip ratio tend to be more fertile than those who have a higher or lower waist-hip ratio. This is a clear example of the way that natural selection has sculpted.
Ancestral men who preferred women with this figure tended to mate with more fertile women,and so had more children.Our preference were passed on to our offspring.
Just as natural selection endowed us with appetites to make us seek out the most nutritious food, so it endowed us with a sense of beauty to make us seek out mates with high-quality genes.
Selecting a Mate for Parental Care
The other way in which your mate affects the survival chances of your offspring is by providing—or failing to provide—parental care.Not all sexually-reproducing species care for their young.In some species,the offspring are left to fend for themselves as soon as they are born.Of the species that do care for their young,most leave the task entirely to the mother.
With humans,it is much more common for fathers to take an active role in providing protection and resources for their children.
In the jargon of evolutionary biology,the human species shows an unusually high level of “male parental investment”.
Human Pair Bonds
Human children,then,are typically cared for not just by a single mother,but by a mother and father together.
Unlike other primates,human parents from stable “pair-bonds”—long-lasting monogamous relationships—to care for their children.And we have been doing this for millions of years.
Parental Care and Human Brain Size
This probably played an important part in the massive increase in brain size that took place during the past few million years of human evolution.Big brains are expensive organs that take time to develop.
During this time,the infant cannot take care of itself and must be looked after by others.Humans have bigger brains,relateve to the size of their bodies,than any other animal.Human infants thus take longer to become independent than the offspring of any other species.
The time and energy required to care for a growing human infant cannot be provided by a single parent acting alone.
Will You Make a Good Parent?
When choosing a mate,therefore,our ancestors had to consider not just the quality of the mate’s genes,but also the mate’s capacity and willingness to invest time and energy in helping to bring up the children.
This poses a different problem.Physical appearances do not provide any clues to a person’s capacity and willingness to invest in parenting.
If you want to get information about whether someone will make a good parent or not,you have to pay attention to their behaviour,not their physical appearance.
What behavioural clues indicate that someone will make a good parent?Parenting is a cooperative venture,a particular kind of alliance,so the same criteria that allow us to decide who will be a good ally in general can be used to determine if someone will make a good parent for one’s own children.
Anything that indicates kindness,patience,generosity and trustworthiness will be a useful clue to parenting ability.So natural selection should have favoured the incorporation of these criteria in the mate-selection module.
And there is evidence that this is indeed the case.All over the world,people of both sexes say that these are the characteristics they most desire in a long-term partner.
Sex Difference in Mate Preferences
The minds of men and women are largely identical,because most of the adaptive problems faced by our ancestors were the same for men and women.The problem of avoiding predators was largely the same for both sexes,as was the problem of eating the right food,the problem of forming alliances,and the problem of mind-reading.
So we should expect the modules concerned with these tasks to be largely identical in both sexes.Fine.But when it comes to choosing a partner—what then?What about the mate-selection modules?Do men and women differ in their mate preferences? Many of the problems involved in choosing a long-term mate were identical for both sexes.
We both want parteners who can contribute good genes and parental care of their offspring.But these are other problems involved in choosing a mate that differ for men and women.
These different problems required different solutions,and so we should expect the mate-selection modules of men and women to reflect these differences.
Dads and Cads
Choosing a mate poses different problems for men and women because the same reproductive strategies are not available to both sexes.Both sexes can look for a long-term partner and establish a pair-bond with them to rear children together.Biologists refer to this as a “long-term mating strategy”,and it is the same for both men and women.The alternative is the “short-term mating strategy”.This option is also available to both sexes,but not in the same way.
“For us,the short-term mating strategy involves having sex with a woman and then abandoning her to look after the baby. Clearly,this is not a viable option for us,because it is women,not men,who get pregnant. ”
This difference between men and women posed an adative problem for ancestral women.They had to be able to tell the difference between a man who was pursuing a long-term mating strategy and a man who was pursuing a short-term mating strategy.Women who could not tell the difference ran the risk of becoming single mothers,which lowered their child’s chances of survival.Natural selection endowed women with various mental mechanisms to help them avoid this fate.One such mechanism lies behind the delaying tactics of women.Women tend to be more cautious then man about having sex.
“We’re more willing to delay the moment to have sex with someone we like.” “During this waiting period,she may try to extract material resources from me as proof of my commitment to her.”
In ancestral environments,this was a way of making sure that the man was interested in a long-term relationship and was not simply looking for a one-night stand.
Battle of the Sexes—or Evolutionary Arms Race?
However,if ancestral women had never agreed to have sex without looking for signs of commitment from the man,then natural selection would have eliminated those men who could not show signs of commitment.
“We would never have been able to have sex—so our genes would have quickly died out.Perhaps some of us would have become good at tricking women into having sex by feigning commitment and then deserting.But then natural selection would have favoured those us who were good at detecting liars—and the liars would have been eliminated.”
The Myth of the Monogamous Female
Since the male tendency to pursue casual sex has clearly not died out,this must be because ancestral women were not completely monogamous either.The idea that men only want casual sex,while women only want commitment,is not supported by evolutionary psychology.
Both sexes use both long-term and short-term mating strategies.
Women’s Extra-Pair Mating
But what advantages could women derive from casual sex?If women did not have the option of leaving men holding the baby, why would they have bothered with a short-term mating strategy?
One possibility is that ancestral women may have used the short-term mating strategy for purposes other than reproduction.For example,ancestral women may have swapped sex for food,much as chimpanzees do today.
Another possibility is that an ancestral women who was already in a long-term relationship might have had casual sex with other man and then pased the resulting children off as her partner’s.
This “cuckold strategy”gets a woman the best of both worlds.A diverse mix of genes from her various lovers—and the resources of her doting partner.
This is the female version of the short-term mating strategy.
What’s the best Strategy?
Even with these potential benefits,however,casual sex was still riskier for ancestral women than for ancestral men.Those women without a long-term partner could still be left holding the bady,and those with a long-term partner ran the risk of being discovered and punished.So natrual selection favoured women who were more cautious about having casual sex than men.
Even though both sexes use short-term mating strategies.They do not use them to the same extent.
Men are more inclined to pursue the short-term strategy than women because it is less costly and the benefits are potetially much greater to them.A man who has sex with a thousand women can potentially have a thousand children.But a women can only have a few chidren in her lifetime,no matter how many men se has sex with.
Men with Resources
Because women preferred a long-term mating strategy,men who did not look as if they would be good fathers were less successful in the mating game.So natural selection favoured men who looked as if they would be good fathers.What are the things that make a man a good father?In the world of the stone-age,a key factor in being a good father was being able to provide resources for the child.So females should have evolved preferences for men with the capacity to acquire costly resources.Mae West,the diva of film comedy,summed it up.
Women like a man with a past,but they prefer a man with a present.
Testing Mate Preferences
In the 1980s,an American psychologist called Dvid Buss set out to test these evolutionary predictions about mate preferences.If mate preferences have evolved by natrual selection,they should be cross-cultural and universal.So Buss and his team carried out interviews with over 10,000 people in 33 countries located on six continents and five islands.
In one experiment,women stated that they were unwilling to go out with,have sex,or marry the men in low-status costumes,but were willing to consider all these relationships with men in high-status clothes,even though it was the same man in all the pictures. “We cound that in every country,women valued ‘good finacial prospects’in a potential mate more highly than men did.The evolutionary prediction about female preference for men with resources was confirmed.”
As with most studies of differences between men and women,the data obtained by Buss showed a big overlap in the scores of each sex.Nevertheless,the difference between the average of all mate values and the average of all female values was often staistically significant.When discussing the difference between men and women,it is important to remember that we are talking about averages of groups,and not individuals.Some men are shorter than some women,but it’s still true than men are,on average, taller than women,and that difference needs explaining.
Attractiveness and Age
Buss’s survey also showed that,all over the world,women prefer mates older than they are.This may also be related to the female preference for men with the capacity to acquire resources.
“Men tend to get better at acquiring resoureces as they get older.Men,on the other hand,universally prefer younger mates.”
The evolutionary explanation for this is that reproductive success is much more related to age in women than it is in men.