Chapter 12                       The Mechanism of Cultural Evolution

   

            

             Customs: Geisha Dancers (credit: Joi Ito, via Wikimedia Commons)

In order to begin to build a universal moral code, we must now create a model of cultural evolution, one that is reasonable and testable, as theories in Science are supposed to be. In order to set up our model, first, we’ll describe some data, i.e. describe how a number of different beliefs, morés, and customs have worked in the real lives of several different tribes/nations.

Second, we’ll infer from our observations of the data, a theory/model of how moral codes work: how a moral code shapes behavior, how new parts are sometimes added to that code, and how, sometimes, old parts are dropped.

Finally, to complete this part of our overall case, we’ll test the theory against more data.

   

                  

        A recent custom: dabbing (credit: Gokudabbing, via Wikimedia Commons) 

The testing of our theory will have to be ex post facto. That is, we could never intentionally program a new code of behavior into a test population even of a few hundred people just to see how, over a dozen generations or so, that code would affect their survival rate. That would be morally forbidden under the code of ethics we now live by in the West. We can’t purposely, consciously usurp the freedom and dignity of other people for reasons of research or any other reasons. But we can examine the records we have of human tribes – their stated beliefs and values, and the acts people in those tribes performed in real life. In short, via a study of History, we should be able to put together a model that tentatively explains why humans do the things they do. 

Most of us are conditioned to be fiercely loyal to the way of life that we grew up with so we can expect that analyzing the roots of morality will be hard. Powerful programming steers us away from any such analyzing. Instead, we are steered toward affirming the values/morés we grew up with. On the other hand, we do have a lot of evidence in historical records of life as it has been lived by real people from which to infer our tentative theory/model.

To begin with, we can observe the everyday actions of the people around us. Why does this man rise when his clock radio beeps? Why does he even own a clock radio? Why do men in some cultures shave off their beards? Why have women in so many cultures for so long been so oppressed? Why is honoring elders such a widespread custom?

In similar ways, dozens of mundane questions may be posed about everyday life in our society or any society. While these actions and the motives behind them may seem obvious to people who live in the society where the customs are practiced, to people from other cultures, the reasons for foreigners’ ways aren’t so much confusing as inscrutable. All nations have at least some “ways” in their daily lives that visitors from other lands see as being not normal.

   

                        

            Dancers in West Africa (credit: Eric Draper, via Wikimedia Commons)

An interesting example of a custom that is commonplace in some societies but not in others is the one that trains men to shave their beards. In some cultures, clean-shaven men are seen as being presentable, neat, and attractive. Socially acceptable. In other cultures, a man without a beard is seen as being weak. 

The fascinating questions come when we ask “Why?” Why is shaving done? Is there a survival advantage in some environments for men who learned from their fathers to shave off their beards? For example, do men who shave daily appear more attractive to women? Do they reproduce more prolifically and thus pass their shaving behavior on to more progeny, i.e. sons who watch their fathers shave and then, when they grow up, do the same themselves?

Research on shaving is sparse and inconclusive. However, what’s important for now is to see that asking these kinds of questions about cultural morés and customs in terms of their possible advantages in the survival game entails thinking scientifically about morés. Under this view, no human customs are trivial. They all have significance in the larger design of a culture. Under this view, we also can compare cultures. Mundane customs become fascinating.

If we keep asking "Why?" about our "ways of life", the answers seem to spread further and further from one another into a variety of human morés and then whole cultures; human morés vary widely within any given society and then much more so from society to society. But if we persist in analyzing our observations, patterns begin to emerge. Based on these patterns, we can make some general statements about people and their ways.

For the most part, people act in the ways that they do because they have been programmed to act in those ways – by parents, teachers, and the media in their cultures. Humans don’t acquire most of their “ways” by genetic coding. We are not born to adopt shaving our beards or speaking English or spicing our food with curry because of “innate” forces pushing us to do these things. The behaviors are learned from those around us as we develop in childhood. 

For example, close observation shows that the vast majority of humans early on in their development learn to urinate and defecate in ways considered socially acceptable in their particular culture. The urge to “go” as we say in English gets urgent to the point of being irrepressible. But where we “go” is very specifically defined by our cultural programming.

      

                           

                                        Balut (soft-boiled fetal duck, Vietnam)

                             (credit: Marshall Astor, via Wikimedia Commons)

In this category of mundane morés, we also find the morés that govern how we eat. I prefer to eat dishes I find familiar, ones I ate during my upbringing. And in my culture, I wash my hands before eating in order to remove disease-causing microbes that I might otherwise ingest with my food if I ate it with dirty hands. I have never seen these tiny animals, but I have been trained to be wary of them. Therefore, I take measures to neutralize the danger I believe they pose to my health. For similar reasons, I try to urinate and defecate only in places deemed acceptable in my society, no matter how acute my natural urges feel.

It is useful to note here the profound way in which human behavior patterns differ from those of nearly all other animals. A turtle doesn’t need ever to see another turtle, from hatching to dying of old age, in order to be turtlish. A turtle that was the last of its species would be unable to perform its genetically driven reproductive behavior each mating season, but for a few days it would still try to find a mate. The rest of the time, it would live in ways normal for turtles, with all its behaviors being directed by its genetic code.

Creatures like ants, crabs, and fish that came early in evolutionary history clearly are more fully programmed by their genetic codes than later ones like cats, dogs, apes, and humans. But even large mammals learn only fractions of their behaviors. Most of their behaviors are still acquired via their genetic programing. Kittens, in time, will stalk balls and then mice and birds, even if they are taken from their mothers still blind and helpless. Pups are genetically programmed to bury bones. As they mature, dogs mate, then have pups, even if they were taken from their mothers at one week old, blind and helpless, and raised by human owners.

Humans, by contrast, if raised by dogs, become doggish, and demonstrate few if any human behaviors. We humans – unlike turtles, apes, and kittens – learn our society’s way of being human by “enculturation”, i.e. almost entirely from other, older humans.^1,2

The knowledge base that you consult most of the time in order to respond to real-life situations is called your culture, and it is learned, not innate. Put a dead fish in the earth with each corn seed that you plant; wear your tuxedo and black tie to the opera. These are customs, not inherent ways.

                                        

                                      

                           A widespread custom: mom teaching daughter how to cook

                       (credit: Sgt. Sinthia Rosario, via Wikimedia Commons) 

But if humans act as they do mostly because of social programming, then we must ask why or how some behavior patterns ever became established at all in the earliest human societies, and why many behaviors possible for humans vanished or never got tried. Why don’t most people on this planet eat holly berries or make their children into slaves? The answer is clear: such practices would reduce the chances of our children surviving to have and raise children of their own and so reduce the chances of our culture surviving. We keep concepts, values, and morés that help us to survive. We drop the ones that don’t. And in this picture, my loyalty to my “way of life” is programmed into me because that programming is my culture’s way of protecting itself.

We keep alive concepts, values, and morés that, in the past, have kept us alive.

Behavior patterns get established in a society and passed on generation to generation if they enable the people who use them to live – as individuals and as tribes – to survive, reproduce, and then program the behaviors into their young. If new morés or behavior patterns are to last, then they must achieve these results at levels of efficiency at least as high as those the community knew before its people began to try out the new behavior patterns. When an old moré no longer serves any of its carrier society’s needs, or when it in fact is getting in the way of serving survival needs, over generations, it dies out. This is the theory around which the model of sociocultural evolution is built.³

Understanding the process by which a new moré enters into the cultural code of a society is vital to our understanding the survival of morés themselves. None of the phases in a society’s adopting a new moré necessarily entails any of the others. A behavior recently acquired by one person on a trial basis may make that individual healthier and/or happier, but this does not automatically mean he will reproduce more prolifically or nurture his kids more effectively or teach his morés to them more efficiently. Other factors can intervene.

Many examples can be cited as evidence to support this model. Some tribes in Indonesia once taught every member of the community to go into the forest to defecate. The individual had to dig a hole in the earth, defecate in it, then cover the excrement with earth before returning to the tribe’s living spaces. The “reason”? Children were taught to hide their excrement so no shaman could find it and use it to cast an evil spell on the child or his/her family.⁴

In the view of Western societies, the advantages of the practice lie in the way it reduces the risk to the community of diseases such as cholera. (We know by our Science that excrement carries microbes, sometimes deadly ones.) Similar practices are taught to people in Western societies (and described in cultural codes as early as those found in the Old Testament of the Bible).

Or consider another of our morés. For centuries, many Europeans drank a lot of tea, hot chocolate, and/or coffee. These customs rapidly became accepted as “traditional”, even though the dates of their introductions into Europe can be specified to within less than a decade. Neither tea nor coffee was a traditional beverage in old European cultures. Scientific reasons for why consuming them was beneficial to human health were not known until germ theory was found, but the benefits were felt by their enthusiastic consumers, nevertheless.

In much of Europe, local water contained dangerous bacteria. But the water for properly made coffee or tea is always well boiled before the tea is brewed. Boiling kills the pathogens. Tea drinkers gained a modest, but real, survival advantage over those who did not like boiled beverages. 

While the benefits were mixed because they were partially offset by the negative effects of caffeine use, the important thing to see is that these people did not need to know anything about bacteria in order to arrive over generations, by trial and error, at a custom that enabled them over the long term to survive in greater numbers. Tea drinkers died much less often during epidemics. Of course, in China, tea drinking had been looked on as a healthful practice for both the individual and the community/society for centuries by the time Western cultures arrived at a similar custom.

                 

   

            

                            (credit: Julius Schorzman, via Wikimedia Commons)

        

   

                                       Innu grandmother and granddaughter

                               (credit: Ansgar Walk via Wikimedia Commons)

Another example of a value and its attached moré that guides our cultures can be found in a different area of life, in the laws of Moses. One of these instructs followers of the Hebrew, Christian, and Muslim faiths to “Honor thy father and thy mother, that thy days may be long in the land that the Lord thy God hath given thee”. (Exodus 20:12) The faithful are instructed to care for, respect, and consult their parents. Therefore, by a small logical extension, all citizens of the community are more likely to be cared for in their old age.

“Honoring” elders means consulting with them on all kinds of matters. But why did this custom have a good survival index?

Before writing was invented, an old person was a walking encyclopedia to be consulted for useful information on treatments for diseases and injuries, planting, harvesting, and preserving food, making and fixing shelters and tools, hunting, gathering, and much more. Knowledge was passed down the generations by oral means. By honoring elders, the people of a tribe preserved, and thus had access to, much larger stores of knowledge than if they had simply abandoned their elderly as soon as they appeared to be a net drain on the tribe’s resources. An elder’s knowledge often solved small problems or sometimes major crises for the entire tribe. In short, it was often just good sense, a good bet, to consult the elderly. Over many generations, societies that respected and valued their elders gradually outlasted, outfed, outbred, outnumbered, and outfought their competitors.

Imagine an elder in a primitive tribe. She might have said: “We have to boil the water. This sickness came once before when I was seven summers old. Only people who drank soup and herb tea did not get sick. All who drank the water got sick and died”. Honoring elders is a tribe-saving policy. It is, every so often, the difference between life and death for the whole tribe. 

          

                                 Secretary Sibelius, Joplin MO (2011)

                            (credit: By HHSgov, via Wikimedia Commons) 

It is worth noting that the Fifth Commandment in its original wording read, “Honor thy father and thy mother, that thy days may be long …” and so on. “Thy” days, not “their” days. At first glance, this seems odd. If I honor my parents, they will likely enjoy a more peaceful and comfortable old age, but that will not guarantee anything about my own final years. By then, my parents, even if they are grateful folk, will most probably be long since dead. At that point, they can’t do much to reciprocate and so to benefit me.

On closer examination though, we see there is more here. As we treat our elders with respect in their last years, consult with them a range of matters, include them in social functions, and so on, we model for our children behaviors that are imprinted on them for a lifetime and they, in turn, will practice these same behaviors in 20 years or so. They will take care of mom and dad. Dad. Me. The commandment turns out to be literally true.

Note also that there is a complex relationship between our morés or patterns of behavior and our values programming. The common behavior patterns in a culture, patterns that we call morés, are just ways of acting out in the physical realm beliefs that are held deep inside each individual’s mental realm, beliefs about what kinds of behavior are consistent with the programmed person’s moral code, i.e. her/his code of what acts are right or wrong, appropriate or inappropriate, sensible or silly. More on these matters as we go along.

Honoring parents enables an increase in the tribe’s total store of knowledge. Not committing adultery checks the spread of sexually transmitted diseases. It also increases the nurturing behaviors of males, as it increases each man’s confidence that he is the biological father of every child he is being asked to nurture. Not stealing and not bearing false witness improve the efficiency of the whole community, especially in commerce.

By this point in our argument, explaining the benefits of more customs and commandments should be unnecessary. A major fact is becoming clear: a moral belief and the behaviors attached to it become well established in a tribe if the behaviors help tribe members who practice them to survive. It is also clear that individuals usually don’t see the long-term picture of the tribe’s survival. They just do what they were raised to believe is right. It’s the society, the tribe, with its whole culture, that benefits from effective values and morés over the long haul.

                         

          

   

                      A retrograde custom in modern times: child labor, Nepal, 2010

                                    (credit: Krish Dulal via Wikimedia Commons)

Children may not enjoy some of the behaviors their elders dictate; they may not enjoy them later when they are adults either. Work is hard. Building shelters is work. Making clothes is work. Gathering food and preserving it for the winter is work. Raising children is work. But for survival, individual happiness is not what matters. Patterns of living that maximize the resources of the tribe over many generations are what matter, and these ways of living do not always make sense to the people being programmed to do them. But tribes that do not teach hard work as one of their values die out.

To illustrate further, another example of a custom that seems counterintuitive to many Western minds, but that works in some contexts, can be offered here. Polyandry allows and encourages one woman to have two or more husbands, legally and with the blessings of the community. It seems counterintuitive to us in the West. But the practice is not only viable in some cultures, it even promotes better survival rates and growing populations.

In some areas of the Himalayas, when a man knows that finding work may require him to be away for an extended period, he can pick a good second husband for his wife. Then he will know that she, his children, his property, and children and property of the other man, will all be protected. If she becomes pregnant while he is away, it will be by a man he has approved of.⁵  As long as all three are faithful to the marriage, the risks of any of them getting an STD remain small. More surviving children is the result. 

All that has been said so far in this chapter has been supporting this hypothesis: a concept, belief, or value, and the behaviors that it fosters get well established in a tribe if the value/belief – with its attached behaviors – improves the odds of its adherents’ survival.

A side note is in order here.

This train of thought on the long-term purposes that morés serve for human tribes also brings us to an implication deeply embedded in our argument. Close analysis of individual human behaviors reveals that a few of them can’t be fully explained by our looking only at their advantages for the tribe.

We can’t reason our way to a moral code for all humans until we accept that humans are capable, at least some of the time, of seeing patterns in the events in their environments. Re-occurring patterns. We call our labels/words for patterns concepts. In short, we have to incorporate into our model the idea that humans are capable of conceptual thought, what we call “reason”.

Our ways of life are not just the results us reacting to the forces in physical reality. Rather, human ways of life also contain carefully reasoned responses to stressors in reality. Often discerned by someone decades before us. But no model of cultural evolution is going to prove adequate to explain it if the model does not see humans as thinking beings, capable of learning concepts – and being able to use them to react effectively to challenging situations.   

Forming mental models of things is what we do when we think. When I think of cats, I mentally form a concept of “cat”. But I never have a cat inside my head. Or a tree, a nail or any of the things I think about. I think with concepts.

In fact, in reality, there are no trees. There are living things that exist by photosynthesis that I find it convenient to call “trees”. But each is an individual living thing. And they differ widely from each other. Deciduous, conifer, bushes, banyan, etc. We make up the terms we need in order to sort memories of real-world things for purposes useful to us. But reality contains no trees. On the other hand, even a caveman can use the concept of a tree to escape wolves. Sometimes, he may urgently need that concept.

Thus, I think with concepts, and I am capable of reaching conclusions by a process that can’t be explained in strictly mechanical ways. The “I” that is most “I” is not made of cats or trees But I can think about concepts of those things (and many others) and reach useful conclusions.

We humans act much of the time in ways that our cultures have programmed us to act, but we also can figure some situations out for ourselves and try new responses to them. We can learn on our own. Sometimes, creative individuals even add new concepts that get accepted into their tribe’s whole culture. They win a lot of others over to drinking tea or washing their hands before eating. The subculture that the converts form then out-survives those who don’t accept the new custom, and in a few generations, the custom is customary.

The school of Psychology called "Behaviorism" comes into direct opposition to our model of human cultural evolution at this point. Behaviorism says that all human behaviors are learned one at a time when the individual gets a reward or a punishment for doing an action. Those actions that consistently get me a reward when I do them I will do more. Those that cause me pain in some way when I do them I will scrupulously avoid in future. Stimulus and response – these two concepts can be used to explain all that we do from the simplest to the most complex of behaviors say the Behaviorists.

In our overall argument, Behaviorism’s model of how humans act is left behind at this point because it does not take into account how we think. It pictures stimuli and responses as being connected in a one-to-one, mechanical way. It then uses mechanical terms to explain individual human behaviors. But in the real world of real human beings, this model doesn’t work very well.

The behaviorist reports that “The organism sees specific colours and shapes (or hears certain sounds), pushes the bar, and gets the food-pellet reward”. For example, a rat sees a light go on in its cage, presses the bar it has learned by trial and error to press, and gets a food pellet. Behaviorists say people do the same: go to work at the factory, punch a timecard at the clock beside the door, put bolts on widgets for eight hours, punch out, collect their pay, and go home. This picture of activity, Behaviorists say, portrays how all learning and doing works for all living things – including humans – all the time.

   

                             Bull Moose (credit: Ryan Hagerty, Wikimedia Commons)

But a human can confront situations that are not, by sensory evidence, like anything the human has ever encountered before, and still react effectively. The English hunter who had never seen a moose, kangaroo, or rhinoceros in muskeg, outback, or veldt still knew where to shoot to kill one. 

Polynesian sailors navigated well by the stars of a new hemisphere when they first came to Hawaii as did European sailors when they first began to explore the seas south of the equator. In each of these situations, they were guided by a set of concepts – ideas based on patterns found in large numbers of experiences. For example, a mammal’s heart lies at the bottom of its ribcage, just to the left of center; a heart shot is fatal for every mammal on this planet.

Furthermore, a man may react one way to a new stimulus in his first encounter with it and quite differently in his next encounter, after he has thought about the stimulus situation for a bit longer. He sees a deeper, more general pattern that he recognizes, and then, using concepts stored in his memory, he plans and executes a better response to it. Behaviorism can’t explain such phenomena.

Nearly every human past the age of 10 is capable of forming generalizations based on what he/she learned by experiences and, to an even greater degree, what has been taught by the adults of his tribe. Conceptual thinking is as human as having 46 chromosomes. It comes naturally to a child at about 7 years of age when, for example, he realizes that the short, wide cup holds more soda than the tall, slim one. Volume is a concept. (I take Piaget as my guide here.⁶)

The programmers of society – parents, teachers, shamans, and others – make use of this faculty in their young subjects, greatly increasing these children’s chances of surviving by programming them with more than simple, one-to-one responses to common, recognizable sense-data patterns in the tribe’s territory. The young subject is programmed with concepts and then, at higher levels of generality, with principles, beliefs, and values. These enable that young subject to respond to, and handle, new situations, for example recognizing that a new animal or plant can be used for food or recognizing that a new animal is likely harmful. (“This snake may be small, but it probably has a poisonous bite; their kind nearly always do”.)

Our capacity to think – to use concepts – gives us an advantage over other species on this planet. This human capacity to think in concepts, combined with our capacity to communicate, is what enables us to devise and try new behaviors/morés and thus, enables cultural evolution.

A thinking individual can imagine a new way of getting food, chipping flint, or curing a disease, then test it, and then tell it to her/his fellows. A few try the new way. If it works, and is not threatening some other moré that is “sacred” for the tribe, the new moré gets taken up. The tribe evolves. Not by genetic variations, but by cultural ones, i.e. by the tribe acquiring a new idea that gets good results.

  

      

   

            

                                                     Reindeer with herdsmen

                           (credit: Mats Andersson, via Wikimedia Commons)

Every tribe has labels (words) for large groups of similar things or events in the tribe’s environment. These category terms are taught to the young because they are useful in the quest for survival. The Sami (Laplanders) have many words for reindeer because they often need to differentiate between them. A single word to designate a blond, pregnant doe is useful if she is in labor and needs immediate aid. And for Neolithic tribes, it probably was useful to have many terms for rocks – like “flint” – because only certain types of rocks, i.e. flint, could be used to make effective weapons and tools. 

By contrast, most visitors to Lapland speak only of reindeer does, bucks, and fawns, and some may have no words for reindeer at all. Compared to our ancestors, most of us today also know little to nothing about types of flint.

The word principle is a term for patterns that are common in larger groups of things. Terms like danger and edible name general principles that a tribe has spotted in many experiences of many members. Terms for principles are harder to learn than ones like tiger or apple, but worth learning because they are very useful in the real world. The term danger enables tribe members to tell one another quickly to get away from something. It covers crocodiles, tigers, snakes, bears, unstable cliffs, quicksand, poison ivy, etc. It’s an efficient term so it is worth learning and keeping. I avoid snakes on principle.

The term edible covers nuts, berries, maggots, eggs, frogs, fish, most lizards, mammals, most mushrooms, and many more things one may come upon within the tribe’s environment. It enables one tribe member to tell another a thing they’re looking at is worth gathering because it can be safely eaten.

   

                 

                                      Weird-looking, but edible: California spiny lobster

                         (credit: Dr. Kjaergaard [assumed], via Wikimedia Commons) 

                        

                         

                                       “Poverty” is a word for a very general concept

                Migrant Mother (credit: Dorothea Lange, via Wikimedia Commons)

Early tribes gradually learned that more general terms – if they accurately described larger classes of things in reality – could be very useful because more general terms help us to design more accurately and quickly behaviors that will more often be effective in our struggle to survive. Surviving is a little easier for things that can think.  

Thus, finally, by this process of greater and greater generalizing, we come to values, the most general of principles; they apply to very large stores of memories of sense data. We are taught to care deeply about them – about understanding a term like right – ultimately, because we want to survive in greater numbers over the long run. So we are taught to “do the right thing”.

Terms for values name meta-behaviors, programs that are called up and run within our brains. We use values terms learned from our mentors and teachers to form judgments about what we are seeing all the time. Values enable us to prioritize and thus enable not just actions, but whole ways of life. They enable us to decide, second by second, about all we see: Important or trivial? Hazard or opportunity? Act or not? Now? Soon? Later? Ever? How?  

Note also that most of the time we don’t take any action when an experience is making us think with one of our value-concepts. Often, we recognize a thing is trivial, so we cease to think about it. Noting details in our surroundings does not always mean we respond to them in any way that shows on the outside. Thinking, even thinking about our ways of thinking and which of them have been getting good results lately, is internal activity. To the frustration of the Behaviorists, who aim to study only what is objectively observable, what shows outwardly when we are thinking is often nothing at all. Conceptual thought is as human as having 46 chromosomes. It is the single biggest reason why we dominate our planet as we do. But it is often not reducible to a series of observable, measurable behaviors.

   

                        

                  Modern medical theory(concepts) handling reality: vaccination

                           (credit: Andrew McGalliard, via Wikimedia Commons) 

Some ways of thinking enhance our chances of finding health and survival. Tribes are always seeking those ways. Ways of thinking that work effectively over generations are the ones we keep and teach to our kids. Conversely, people who live by principles and values that don’t work don’t survive and, thus, don’t have descendants.

Values help us to organize our sense data and memories of sense data. Over generations, they help tribe members, individually and jointly, to formulate effective plans of action in timely ways. In modern terms, we say values "inform" our thinking. Since reality is always changing, our values must evolve also, though as I said above, it is sometimes only by the pain of famine, plague, or war that we amend or re-write our largest values/moral codes. 

So, now let’s consider more data/evidence: the ways in which early humans probably formed and used early examples of principles and values. Let’s test the theory further.

Notes

1.  http://www.bbc.com/culture/story/20151012-feral-the-children-raised-by-wolves.

2. “Enculturation,” Wikipedia, the Free Encyclopedia. Accessed April 20, 2015.http://en.wikipedia.org/wiki/Enculturation.

3. “Sociocultural evolution,” Wikipedia, the Free Encyclopedia. Accessed April 20, 2015.

http://en.wikipedia.org/wiki/Sociocultural_evolution#Contemporary_discourse_about_sociocultural_evolution.

4. Pearson Higher Education, “Anthropology and the Study of Culture”

Chapter 1, p. 17. 

http://www.pearsonhighered.com/assets/hip/us/hip_us_pearsonhighered/samplechapter/0205949509.pdf.

5. Alice Dreger, “When Taking Multiple Husbands Makes Sense,” The Atlantic, February 1, 2013.

http://www.theatlantic.com/health/archive/2013/02/when-taking-multiple-husbands-makes-sense/272726/.

6. “Piaget’s theory of cognitive development,” Wikipedia, the Free Encyclopedia

 Accessed April 20, 2015.                                                                                         

http://en.wikipedia.org/wiki/Piaget’s_theory_of_cognitive_development.