Nature vs. Nurture

INTRODUCTION

The nature versus nurture debates concern the relative importance of an individual's innate qualities ("nature") versus personal experiences ("nurture") in determining or causing individual differences in physical and behavioral traits. The view that humans acquire all or almost all their behavioral traits from "nurture" is known as Tabula Rasa ("blank slate"). This question was once considered to be an appropriate division of developmental influences, but since both types of factors are known to play such interacting roles in development, modern psychologists consider the question naive - representing an outdated state of knowledge.

APPROACHES

The Scientific Approach:

In order to disentangle the effects of genes and environment, behavioral geneticists perform adoption and twin studies. Behavioral geneticists do not generally use the term "nurture" in order to explain that portion of the variance for a given trait (such as IQ or the Big Five personality traits) that can be attributed to environmental effects. Instead, two different types of environmental effects are distinguished: shared family factors (i.e., those shared by siblings, making them more similar) and nonshared factors (i.e., those that uniquely affect individuals, making siblings different). In order to express the portion of the variance that is due to the "nature" component, behavioral geneticists generally refer to the heritability of a trait.

With regard to the Big Five personality traits as well as adult IQ in the general U.S. population, the portion of the overall variance that can be attributed to share family effects is often negligible. On the other hand, most traits are thought to be at least partially heritable. In this context, the "nature" component of the variance is generally thought to be more important than that ascribed to the influence of family upbringing. In her Pulitzer Prize-nominated book The Nurture Assumption, author Judith Harris argues that "nurture," as traditionally defined in terms family upbringing and socioeconomic status, does not effectively explain the variance for most traits (such as adult IQ and the Big Five personality traits) in the general population of the United States. On the contrary, Harris suggests that either peer groups or random environmental factors (i.e., those that are independent of family upbringing) are more important than family environmental effects

Although "nurture" has historically been referred to as the care given to children by the parents, with the mother playing a role of particular importance, this term is now regarded by some as any environmental (not genetic) factor in the contemporary nature versus nurture debate. Thus the definition of "nurture" has been expanded in order to include the influences on development arising from prenatal, parental, extended family and peer experiences, extending to influences such as media, marketing and socio-economic status. Indeed, a substantial source of environmental input to human nature may arise from stochastic variations in prenatal development.

Philosophical Approach:

While classical theories regarding these matters were primarily concerned with the line between that which was voluntary (the ego, the self, and the personal will) and the involuntary (of Nature, Gods, etc.), this view was self-centric, which is to say deferential to authorities over the personal concepts; i.e. religious teaching and doctrine.

As science developed with new understandings of life's elemental nature (determined in its nature and behavior by the behaviors of constituent elements and prevailing physical phenomena, e.g. atoms, molecules, genes, force, and time), the categories that classical formalism defined came to be seen as arbitrary, and the trend of science since has been to develop away from the human-centered view to a more elemental, deterministic, reductionism view. Scientific culture to this day functions within a social boundary imposed by the prevalence among laypeople of classical views. This boundary contains the impact of any scientific discoveries or observations on matters of human society. Thus nature versus nurture debates can be seen as attempts to fit new scientific ideas and developments into the classical formalist and self-based mold, since these debates arose from problems associated with reconciling the formalist notions of classical theories with emerging theories and new data. The gap between prevailing scientific opinion and prevailing lay opinion is reflected in popular science.

Advocates of a formalist view may discount completely the influence of one contributor or the other for the sake of some agenda, for example denying the influence of "nature" in order to preserve the idea of free will as the sole important determinant of behavior, a notion held to be of central importance in many religious, ethical, and legal systems, particularly in establishing culpability.

Heritability Estimates:

Current thinking in biology discredits the notion that genes alone can determine a trait because genes are never sufficient in isolation. At the molecular level, DNA interacts in complex ways with signals from other genes and from the environment. At the level of individuals, particular genes influence the development of a trait in the context of a particular environment. Thus, measurements of the degree to which a trait is influenced by genes versus environment will depend on the particular environment and genes examined. In many cases, it has been found that genes may have a substantial contribution, including psychological traits such as intelligence and personality. Yet, these traits may be largely influenced by environment in other circumstances, such as environmental deprivation.

A researcher seeking to quantify the influence of genes or environment on a trait needs to be able to separate the effects of one factor away from that of another. This kind of research often begins with attempts to calculate the heritability of a trait. Heritability quantifies the extent to which variation among individuals in a trait is due to variation in the genes those individuals carry. In animals where breeding and environments can be controlled experimentally, heritability can be determined relatively easily. Such experiments would be unethical for human research. This problem can be overcome by finding existing populations of humans that reflect the experimental setting the researcher wishes to create. One way to determine the contribution of genes and environment to a trait is to study twins. In one kind of study, identical twins reared apart are compared to randomly selected pairs of people. The twins share identical genes, but different family environments. In another kind of twin study, identical twins reared together (who share family environment and genes) are compared to fraternal twins reared together (who also share family environment but only share half their genes).

Another condition that permits the disassociation of genes and environment is adoption. In one kind of adoption study, biological siblings reared together (who share the same family environment and half their genes) are compared to adoptive siblings (who share their family environment but none of their genes). Some have rightly pointed out that environmental inputs affect the expression of genes. This is one explanation of how environment can influence the extent to which a genetic disposition will actually manifest. The interactions of genes with environment, called gene-environment interaction, are another component of the nature-nurture debate. A classic example of gene-environment interaction is the ability of a diet low in the amino acid phenylalanine to partially suppress the genetic disease phenylketonuria. Yet another complication to the nature-nurture debate is the existence of gene-environment correlations. These correlations indicate that individuals with certain genotypes are more likely to find themselves in certain environments. Thus, it appears that genes can shape (the selection or creation of) environments. Even using experiments like those described above, it can be very difficult to determine convincingly the relative contribution of genes and environment.

Interaction of genes and environment: In only a very few cases is it fair to say that a trait is due almost entirely to nature, or almost entirely to nurture. In the case of most diseases now strictly identified as genetic, such as Huntington's disease, there is a better than 99.9% correlation between having the identified gene and the disease and a similar correlation for not having either Examples of environmental, interactional, and genetic traits are:

Predominantly Environmental Interactional Predominantly Genetic Specific Language Height Blood type Specific Religion Weight Eye color Skin color

The "two buckets" view of heritability.

More realistic "homogenous mudpie" view of heritability. Steven Pinker (2004) likewise described several examples: Concrete behavioral traits that patently depend on content provided by the home or culture—which language one speaks, which religion one practices, which political party one supports—are not heritable at all. But traits that reflect the underlying talents and temperaments—how proficient with language a person is, how religious, how liberal or conservative—are partially heritable. When traits are determined by a complex interaction of genotype and environment it is possible to measure the heritability of a trait within a population. However, many non-scientists who encounter a report of a trait having certain percentage heritability imagine non-interactional, additive contributions of genes and environment to the trait. As an analogy, some laypeople may think of the degree of a trait being made up of two "buckets", genes and environment, each able to hold a certain capacity of the trait. But even for intermediate heritabilities, both genetic dispositions and the environments in which people develop, merely with greater and lesser plasticities associated with these heritability measures always shape a trait.

NATURE VERSUS NURTURE IN THE IQ DEBATE

Evidence suggests that family environmental factors may have an effect upon childhood IQ, accounting for up to a quarter of the variance. On the other hand, by late adolescence this correlation disappears, such that adoptive siblings are no more similar in IQ than strangers. Moreover, adoption studies indicate that, by adulthood, adoptive siblings are no more similar in IQ than strangers (IQ correlation near zero), while full siblings show an IQ correlation of 0.6. Twin studies reinforce this pattern: monozygotic (identical) twins raised separately are highly similar in IQ (0.86), more so than dizygotic (fraternal) twins raised together (0.6) and much more than adoptive siblings (~0.0). Consequently, in the context of the "nature versus nurture" debate, the "nature" component appears to be much more important than the "nurture" component in explaining IQ variance in the general adult population of the United States.

NATURE VERSUS NURTURE IN PERSONALITY TRAITS

Personality is a frequently cited example of a heritable trait that has been studied in twins and adoptions. Identical twins reared apart are far more similar in personality than randomly selected pairs of people. Likewise, identical twins are more similar than fraternal twins. Also, biological siblings are more similar in personality than adoptive siblings. Each observation suggests that personality is heritable to a certain extent. However, these same study designs allow for the examination of environment as well as genes. Adoption studies also directly measure the strength of shared family effects. Adopted siblings share only family environment. Unexpectedly, some adoption studies indicate that by adulthood the personalities of adopted siblings are no more similar than random pairs of strangers. This would mean that shared family effects on personality are zero by adulthood. As is the case with personality, non-shared environmental effects are often found to out-weigh shared environmental effects.

That is, environmental effects that are typically thought to be life shaping (such as family life) may have less of an impact than non-shared effects, which are harder to identify. One possible source of non-shared effects is the environment of pre-natal development. Random variations in the genetic program of development may be a substantial source of non-shared environment. These results suggest that "nurture" may not be the predominant factor in "environment".

Advanced techniques:

The power of quantitative studies of heritable traits has been expanded by the development of new techniques. Developmental genetic analysis examines the effects of genes over the course of a human lifespan. For example, early studies of intelligence, which mostly examined young children, found heritability measures of 40 to 50 percent. Subsequent developmental genetic analyses have found that genetic contribution to intelligence increases over a lifespan, reaching a heritability of 80 percent in adulthood. Another advanced technique, multivariate genetic analysis, examines the genetic contribution to several traits that vary together. For example, multivariate genetic analysis has demonstrated that the genetic determinants of all specific cognitive abilities (e.g., memory, spatial reasoning, processing speed) overlap greatly, such that the genes associated with any specific cognitive ability will affect all others. Similarly, multivariate genetic analysis has found that genes that affect scholastic achievement completely overlap with the genes that affect cognitive ability. Extremes analysis, examines the link between normal and pathological traits. For example, it is hypothesized that a given behavioral disorder may represent an extreme of a continuous distribution of a normal behavior and hence an extreme of a continuous distribution of genetic and environmental variation. Depression, phobias, and reading disabilities have been examined in this context. For highly heritable traits, it is now possible to search for individual genes that contribute to variation in that trait. For example, several research groups have identified genetic loci that contribute to schizophrenia (Harrison and Owen, 2003). Moral difficulties: eugenics, etc.

Some observers believe that modern science tends to give too much weight to the nature side of the argument, in part because of social consciousness. Historically, much of this debate has had undertones of racist and eugenicist policies — the notion of race as a scientific truth has often been assumed as a prerequisite in various incarnations of the nature versus nurture debate. In the past, heredity was often used as "scientific" justification for various forms of discrimination and oppression along racial and class lines. Works published in the United States since the 1960s that argue for the primacy of "nature" over "nurture" in determining certain characteristics, such as The Bell Curve, have been greeted with considerable controversy and scorn. A critique of moral arguments against the nature side of the argument could be that they cross the is-ought gap. That is, they apply values to facts.

Philosophical difficulties: are the traits real? It is sometimes a question whether the "trait" being measured is even a real thing. Much energy has been devoted to calculating the heritability of intelligence (usually the I.Q., or intelligence quotient), but there is still some disagreement as to what exactly "intelligence" is. Philosophical difficulties: Biological determinism:

If genes do contribute substantially to the development of personal characteristics such as intelligence and personality, then many wonder if this implies that genes determine who we are. Biological determinism is the thesis that genes determine who we are. Few if any scientists would make such a claim; however, many are accused of doing so. Defining the words "who" and "am" also present philosophical difficulties. Others have pointed out that the premise of the "nature versus nurture" debate seems to negate the significance of will. More specifically, if our genes, determine all our traits by our environment, by chance, or by some combination of these acting together, then there seems to be little room for free will. In any case, this line of reasoning suggests that the "nature versus nurture" debate tends to exaggerate the degree to which individual human behavior can be predicted based on knowledge of genetics and the environment. It should also be pointed out that biology may determine our abilities, but free will still determines what we do with our abilities. Philosophical difficulties: is the problem real?

Many scientists feel that the very question opposing nature to nurture is a fallacy. Already in 1951, Calvin Hall in his seminal chapter remarked that the discussion opposing nature and nurture was fruitless. If an environment is changed fundamentally, then the heritability of a character changes, too. Conversely, if the genetic composition of a population changes, then heritability will also change. As an example, we may use phenylketonuria (PKU), which causes brain damage and progressive mental retardation. PKU can be treated by the elimination of phenylalanine from the diet. Hence, a character (PKU) that used to have a virtually perfect heritability is not heritable any more if modern medicine is available. Similarly, within, say, an inbred strain of mice, no genetic variation is present and every character will have zero heritability. If the complications of gene-environment interactions and correlations (see above) are added, then it appears to many that heritability, the epitome of the nature-nurture opposition, is "a station passed".

Myths about identity:

Within the debates surrounding cloning, for example, is the far-fetched contention that a Jesus or a Hitler could be "re-created" through genetic cloning. Current thinking finds this largely inaccurate, and discounts the possibility that the clone of anyone would grow up to be the same individual due to environmental variation. For example, like clones, identical twins are genetically identical, and unlike the hypothetical clones share the same family environment, yet they are not identical in personality and other traits.

"NATURE" IS MORE INFLUENTIAL THAN "NURTURE":

Knowledge arises from genetic information honed by a process of natural selection. Some portions of this knowledge might be nurtured, but genetically determined forms also may modify how we categorize our experiences.

Evolutionary view:

From an evolutionary point of view, certain things we know about the world are innate, although modifiable by interactions with family, education, religion and society. This knowledge about objects and what is valued is "natural" having been selectively reinforced over time. For instance, pack behavior observed in wolves is a form of collective behavior that supports kinship preferences and caring, while perpetuating a common genetic pool.

During the 1800's, Charles Darwin speculated that certain rules for conflict arbitration were needed at the point in time when a species evolved a longer memory, a keener imagination and became involved in social contracts. For example, a bird, which could leave an active nest to migrate with her group, choosing that instinct over the one to nurture, would find this choice too difficult with a better memory. He argued that certain instincts, such as caring for young as opposed to making a rapid decision to leave, were preferentially selected in any conflict because those values had longer lasting consequences. (30) A reasonable alternative interpretation might be that those behaviors encouraging the survival of young also perpetuated those genes that might select for altruism at least among relatives. This form of altruism enhances the survival of the genotype of the altruist. Altruism for non-relatives is quite a different story because the personal pay-off or gain is less easily discerned.

Neurological studies:

Oliver Sacks, author and neurologist, has devoted much of his recent book to describing the unique behavior of a group of his patients who are savants.(37) A savant is someone who demonstrates an extraordinary talent in a particular field such as art, music, or mathematics. Sacks became "friends" with a young boy named Stephen, who was an autistic savant, capable of memorizing complex scenery at a glance and retaining the information for months. When asked he would accurately construct a pen and ink sk etch from what he had observed earlier. He started his pictures at one edge of the paper, working across to the other edge, filling in the framework and all the details without an outline. While drawing, "the house could come down" and Stephen would not notice. He sometimes took artistic license and added features, which did not originally exist, but the basics, the original flavor, remained. In a sense, having demonstrated his enormous talent at an early age, he had little need for nurture - from the environment or from other humans.

Philosophical discussion:

In examining the relationship between what was inherited and what was learned from experience, philosophers Hume and Kant were echoed by the behaviorist, Freud, when they spoke of nature's contribution as a force to be reckoned with, educated or subdued. Human nature was always a "fact" to contend with. In a more extreme view from the 1500's, Descartes questioned whether anything existed outside of the mind. He finally conceded that if there were real things instead of only our thoughts about them, God was responsible for the interpretation. Kant, who realized that Descartes' position made all knowledge subjective to each individual, tried to move away from this restrictive view and proposed that the mind was an active participant in knowledge acquisition, constructing certain aspects of an experience. Kant believed we inherited certain categories or concept grids on which experiences could be sorted or organized.

To understand how the mind might "construct" an experience, the following experiment should be helpful. Obtain three bowls each holding about a gallon of liquid. Arrange them so that the first bowl contains hot water; the second, tepid; and the third, very cold water. Simultaneously, place your left hand in the hot water and you right in the cold. Wait one minute and immerse both hands in the tepid water. What has each hand told you about the temperature? Additional examples of the mind's involvement in interpreting experience are seen with optical illusions, the unnoticed retinal "blind spot" and other adaptive behaviors found in the nervous system. One of the problems with a purely "nature" based argument is how to explain the existence or continuing survival of certain values which may involve actions for which there is no obvious natural selection pressure. For example, why should a choice be made contrary to an individual's stated preferences or which may result in actual punishment? Altruism for non-related individuals, truthfulness and justice as fairness are values difficult to support from an evolutionary view, particularly when some choices cause the death of an individual, effectively removing those genes from the pool. Hypothesizing these as primarily inherited values would generate a requirement for a very complex set of genetic directions having a large common human base of reference. The search for a potential common morality has provoked more debate than agreement among anthropologists, theologians, and philosophers.

INTELLIGENCE - NATURE VS. NURTURE

Environment is more important than genes when it comes to intelligence, politically corrected scientists keep telling us. If this is true, however, then it would follow that the Homo Sapiens of 20,000 years ago was not as intelligent as we are today.  However, these very same 'scientists' keep telling us that we are no more intelligent than the very first human beings! But they simply cannot be right on both counts - unless they also argued that 20,000 years of 'environmental progress' and change achieved absolutely nothing in the way of developing our intellect.  But if they argued this, they would then scupper their own notion that the environment was important! 

After all, the environment that surrounds, let's say, city-dwellers, right now, is VASTLY different from the environments and conditions of 20,000 years ago. If such enormous changes haven't altered intelligence levels, then what environmental changes will? Also, if environment is extremely important when it comes to intelligence, then it follows that those brought up in more primitive environments are less intelligent than those brought up in more 'enriched' environments.  And this must mean that simple, primitive, isolated 'tribal folk' are less intelligent than 'civilized' folk who live in places that are 'enriched', and where experts provide a mountain of education to those who study and learn from them. But politically corrected 'scientists' would also deny this!  And by doing so, they again scupper their own notion that the environment is important.

If the environment is of greater significance than heredity when it comes to intelligence - as politically-corrected 'scientists' would have you believe - then it also follows that poorer folk should be less intelligent than richer folk, that those doing dull boring jobs should be less intelligent than those doing stimulating ones, and that women throughout the ages (who were, apparently, oppressed into domestic servitude for most of their lives) were less intelligent than their men - throughout the whole of History! And, of course, politically corrected 'scientists' would also deny all of these things.  In short, politically corrected scientists simply cannot have it both ways - unless they fudge, duck, dive, twist, deceive, distort and lie.

Nature vs. Nurture - What do you think?

In looking for the causes of individual differences in intelligence, a major issue is the relative contribution of genetics and environment.  

  100% Genetics (Nature) 90% Gen. 80% Gen. 70% Gen. 60% Gen. 50-50 60% Env. 70% Env. 80% Env. 90% Env. 100% Environ. (Nurture)  

Rate the extent to which you believe nature and nature influence (cause) human intelligence. Warning!  As you learn more about the theory and research on genetic and environmental influences on human intelligence, you may find that you change some of your beliefs and assumptions.

Pendulum of opinion on Nature vs. Nurture through history The zeitgeist (the intellectual and culture "flavor" of a time and place) has swung back and forth over time with regard to the amount of influence that nature vs. nature has on human intelligence.

·1 For example, in the late 1800's in the UK, as Darwinism took off, the role of genetically determined capability was considered very important.  ·2 This was in contrast, for example, to the 1960's in the USA, when views were more in favor a "tabula rasa" (blank state) view of human intelligence - in other words, all people are capable of much more, if given conducive environmental conditions in which to reach their potential ·3 Currently the Zeitgeist is the Western psychological world is somewhere in-between - both genetics and environment are seen as playing important roles.  To be more precise, the modern view about nature vs. nurture in intelligence is "interactionist".  This view is well expressed by Ridley (1999, p.77): "Mother Nature has plainly not entrusted the determination of our intellectual capacities to the blind fate of a gene or genes; she gave us parents, learning, language, culture and education to program ourselves with."  

Historical trends in the nature-nurture debate Late 19th century - early 20th century (Nature) From the mid to late 1800's through to the early 1900's opinions rested in the nature camp. This was consistent with the scientific discoveries of the role of inheritance and natural selection by Mendel and Darwin.

The major contributor to the psychological argument was Francis Galton in his book "Hereditary Genius: Its Laws and Consequences” (1869).

Galton had observed that the gifted individuals tended to come from families, which had other gifted individuals. He went on to analyze biographical dictionaries and encyclopedias, and became convinced that talent in science, the professions, and the arts, ran in families. Galton took this observation one step further, to argue that it would be "quite practicable to produce a high gifted race of men by judicious marriages during several consecutive generations".

This suggestion became know as eugenics, "the study of the agencies under social control that may improve or repair the racial qualities of future generations, either physically or mentally."  Galton wanted to speed up the process of natural selection, stating that: "What Nature does blindly, slowly, and ruthlessly, man may do providently, quickly, and kindly”.

Galton was convinced that "intelligence must be bred, not trained". Such arguments have had massive social consequences and have been used to support apartheid policies, sterilization programs, and other acts of withholding basic human rights from minority groups.

Post WWI: 1920’s-1930’s: After World War I, careful reanalysis of the mass of intelligence test data took place. This began to challenge the commonly held view that intelligence was directly, genetically linked to racial differences: ·1 E.g. blacks from Illinois had higher IQ scores than whites from 9 southern states - a finding difficult to reconcile with the simple idea that whites are intellectually superior to blacks. Evidence now seemed to support a closer link between social class and intelligence, rather than race and intelligence. As a result, a number of psychologists in the 1920s and 1930s shifted their position towards the environmental camp.

The shift against 'nature' views was given momentum by the backlash against the social consequences of government policies: ·1 E.g. sterilization laws had been passed in 24 US States, resulting in 20, 000 people being sterilized against their will. 320, 000 people suffered the same fate in Germany.

1940’s-1990’s: The backlash faded, and the pendulum swung back towards the middle. From the early 1940's, it seemed there was a rejection of simplistic nature or nurture views, with more common recognition of their complex interplay. Nevertheless, social prejudices and inequalities were still evident and growing.

Thus, in the 1960's, the focus of the problem was shifted away from the individual as the cause of the problem, and centered on social determinants. The pendulum swung towards the nurture/environmental end and away from the nature/genetic end. Efforts were made to arrest poor educational achievement through special schooling, and to alleviate poor living conditions through welfare.

It became politically correct to minimize talk and discussion of the role of 'nature' in contributing to any individual differences, let alone intelligence. The evidence of differences in intelligence between socioeconomic groups and racial groups, however, did not go away.

Recent trends – "The Bell Curve" controversy:

From time to time, there have been inflammatory articles, which present and interpret evidence of IQ differences between groups (in particular Jensen, 1969). The most recent, and most major of these publications was Herrnstein and Murray's (1994) "The Bell Curve". This book provided momentum to swing the pendulum in the direction of 'nature', at least in the public's eye, but even more so, it generated massive debate and controversy in psychology, sociology, education, and politics, not to mention the media and household. The 800+ page book, written for laypersons, hit the best-seller lists in the U.S. "The work's main thesis is that an individual's intelligence - no less than 40% and no more than 80% of which is inherited genetically from his or her parents - has more effect than socio-economic background on future life experiences." Manolakes (1997), p.235

In addition to the premise that measured intelligence (IQ) is largely genetically inherited, a second important premise was that IQ is correlated positively with a variety of measures of socioeconomic success in society, such as a prestigious job, high annual income, and high educational attainment; and is inversely correlated with criminality and other measures of social failure.

Some sample controversial quotes from "The Bell Curve" ·1 “IQ has more effect on future life experiences than SES” ·2 “Intervention efforts are largely a waste of time and money” ·3 “Increasing population of 'lower caste' intelligences, lessening the nation's 'genetic capital”

Reactions to The Bell Curve:

·1 The Bell Curve" re-ignited the nature-nurture debate. ·2 The public debate was (and is) divided. o The politically left saw the authors as "un-American”;- "pseudo-scientific racists”;- and the book as "alien and repellent" o The politically right saw the authors as: - "brave and respectable scholars,”;- whose book was "lucid" and "powerfully written" ·3 The part of The Bell Curve that captured public attention was on the differences in IQ between African and Caucasian Americans. Further to this were the suggestions made by Herrnstein and Murray about the implications of a predominantly genetically inherited intelligence for public and social policy. Since IQ was largely seen as genetically determined, the authors expressed resistance to educational and environmental interventions. They argued that money spent in this way is wasted. The authors also argued that America is becoming a society of 'cognitive castes', with the lower caste including a large proportion of African-Americans. Hence their statement that the 'genetic capital' of society is being eroded because the less intelligence, lower class is reproducing at a greater rate than high IQ classes.

Evidence in favour of “nature”:

In the heyday of eugenic IQ testing in the 1920s there was no evidence for the heritability of IQ. It was just an assumption of the practitioners. Today that is no longer the case. The heritability of IQ (whatever IQ is!) is now an hypothesis that has been tested - on twins and adoptee. The results really are quite startling. No study of the causes of intelligence has failed to find a certain and often-substantial Concordance rates of IQ scores:

·1 Evidence from family studies provides the main supporting evidence from which arguments about the relative roles of genetics and environment are constructed.

Thomas Bouchard of the University of Minnesota starting in 1979 undertook a large number of the study of twins reared apart. He “collected” pairs of separated twins from all over the world and reunited them while testing their personalities and IQs. Other studies at the same time concentrated on comparing the IQs of adopted people with those of their adopted parents and their biological parents or their siblings. Put all these studies together, which include the IQ tests of tens of thousands of individuals, and the table looks like this:

Same person tested twice 87% ·2 Identical twins reared together 86% ·3 Identical twins reared apart 76% ·4 Fraternal twins reared together 55% ·5 Biological siblings reared together 47% (studies show that reared apart about 24%) ·6 Parents and children living together 40% ·7 Parents and children living apart 31% ·8 Adopted children living together 0% ·9 Unrelated people living apart 0%

Ridley, 1999, p.83 Meta-analytic estimates of the heritability of intelligence A meta-analysis of 9 family studies was conducted by Daniels, Devlin and Roeder (1997): it included 212 correlations and produced very similar results to those quoted by Matt Ridley. These authors conclude that heritability can account for 48% of the variation in IQ. The highest estimates have come from reviews of research by Herrnstein & Murray, 1994 (74%) and Essence (80%). A safer bet is probably to sit on the fence - 50:50!

Heritability indices, however, are not pure measures of genetic inheritance - they included prenatal environmental influences, (e.g. whether the mother smokes, what she eats, etc.) and the postnatal material environment.

Heritability & intelligence:

It must be noted, however, that heritability is not pure genetic influence as the pre and postnatal environments must be taken into account. Heritability estimates based on comparing correlations between IQs of monozygotic (identical) twins reared together with IQs of dizygotic (fraternal) twins and siblings are likely to overestimate the genetic component because monozygotic twins share more similar environments - both in the womb and out ·1 Twins reared apart are not assigned at random to foster or adoptive parents - since homes are selected purposely to with regard to characteristics of the child and characteristics of the family. This would partially account for the IQ correlations attributed to inheritance ·2 Twin studies may not be generalizable to the population at large as twins are more susceptible to prenatal trauma leading to retardation. The inclusion of retarded cases may increase the twin correlation in intelligence test scores. Heritability indexes refer to the population on which they were found at the time and are not applicable to an analysis of test performance between two population groups e.g. ethnic groups. ·3 Heritability does not indicate the degree to which a trait can be modified

In the discussion to date, we have focused on the heritability (or otherwise) of general intelligence. What about the subcomponents of intelligence? There is, indeed, evidence of a greater genetic link for: 1. Spatial ability 2. Reasoning And less evidence for genetic influence on: 1. Divergent thinking 2. Verbal fluency There is, however, relatively little research along these lines.

Evidence in favour of “nurture”:

"Give me a dozen healthy infants & my own specific world to bring them up in, & I'll guarantee to take any one at random & train him to become any type of specialist I might select - doctor, lawyer, artist, merchant, chef & yes, even beggar & thief, regardless of his talents, penchants, tendencies, abilities, vocations, and race of his ancestors." - John B. Watson, 1924 This was a famous quote in the heyday of behaviorism, when the child was considered to be a 'tabula rasa' (blank slate) onto which anything could be sculpted through environmental experience. This would be a 100% environmental view, but virtually no psychologists would accept such an extreme position today.

The Flynn effect: Are we getting smarter:

In the 1980s, a NZ-based political scientist, James Flynn, noticed that IQ was increasing in all countries all the time, at an average rate of about 3 IQ points per decade i.e. the average IQ across the world has risen over 1 standard deviation (i.e. 15 points) since WWII - predominantly due to environmental effects. As a result, new norms continue to be used to rescale IQ tests to '100'. Could this be due to diet? Possibly but IQ scores are still rising just as rapidly in well-nourished western countries. Could it be schooling? Interruptions to schooling only have temporary effects on IQ. Importantly, it is those test s that test abstract reasoning ability that show the steepest improvements. One researcher, Ulric Neisser suggests that the Flynn effect is due to the way we are being saturated with sophisticated visual images: ads, posters, videogame and TV graphics etc - rather than written messages. He suggests that children experience a much richer visual environment than in the past and that this assists them with visual puzzles of the kind that dominate IQ tests.

The evidence for the rise in IQ comes from: • Adoption studies • Nutrition studies • Educational intervention studies

Intelligence varies with at least 21 factors:

Some of the other circumstances and attributes that have been found to vary to a greater or lesser (but always significant) extent in relation with IQ (Bouchard & Segal, 1985; Liungman, 1975) - note that not all of these relationships support an environmental view. Intelligence varies with: ·1 Infant malnutrition (-ve) ·2 Birth weight ·3 Birth order ·4 Height ·5 Number of siblings (-ve) ·6 Number of years in school ·7 Social group of parental home ·8 Father's profession ·9 Father's economic status ·10 Degree of parental rigidity (-ve) ·11 Parental ambition ·12 Mother's education ·13 Average TV viewing (-ve) ·14 Average book-reading ·15 Self-confidence according to attitude scale measurement ·16 Age (negative relationship, applies only in adulthood) ·17 Degree of authority in parental home (-ve) ·18 Criminality (-ve) ·19 Alcoholism (-ve) ·20 Mental disease (-ve) ·21 Emotional adaptation "No single environmental factor seems to have a large influence on IQ. Variables widely believed to be important are usually weak.... Even though many studies fail to find strong environmental effects.... most of the factors studied do influence IQ in the direction predicted by the investigator.... environmental effects are multifactor and largely unrelated to each other." - Bouchard & Segal (1985), p.452 So, it would appear that there are many psychological and biological factors each contributing a small a small fraction to the variance in IQ scores.

Intelligence & race:

Let's focus on some of the correlates of intelligence examining in particular the interplay between race, environment and intelligence; between SES, environment and intelligence; between education, environment and intelligence; and between occupation, environment and intelligence. Herrnstein and Murray (1994) in The Bell Curve state that: • Asians and Asian-Americans have a (.32 standard deviation) higher average IQ than white Americans, and that • white Americans have a (1.58 standard deviation) higher mean IQ than black Americans. Further, they claim that this difference is not a function of cultural testing bias. Herrnstein and Murray (1994) acknowledge that the causes of these differences could be environmental, however the differences in IQ appear to be too large to be accounted for by environmental influences alone. They provide much qualification, cautioning, and warnings about how their evidence should be interpreted In particular, they remind the reader that • IQ is not strongly linked to many so-called 'desirable' human qualities; and • The fallacy of drawing conclusions about individual on the basis of group findings. It would be incorrect to characterize "The Bell Curve" as out-and-out a racist, eugenicist, etc. book. Even detractors acknowledge the importance of its contribution to psychological and social debate.  But the book does, in general, support a view that intelligence is largely heritable.

Note that there have also been investigations into racial differences on subcomponents of intelligence.  Herr stein and Murray (1994) report that: • East Asian scores are typically the same or slightly lower than White American scores on verbal IQ, but much higher on visual-spatial IQ • Black Americans tend to score higher than whites on subtests involving arithmetic and immediate memory, whereas whites typically score high than blacks on subtests of spatial-perceptual ability

Differences in IQ scores between races do not necessarily imply genetic causes. Most psychologists accept that there are group mean differences in IQ scores for non-culturally-loaded tests. However, these differences are confounded with the effects of SES, e.g.

1. Children with black fathers, brought up in white family - no evidence of lower IQs 2. Adoption studies - e.g. black children brought up by white families only slightly lower IQs than white adopted children (Howe, 1997)

Some theorists suggest that socioeconomic disadvantages are the main causes of ethnic differences in IQ.  Even if the variation within a group reflects genetic differences, the average differences between the groups could be wholly due to environmental factors.  Imagine, two pots, with randomly allocated seeds from the same batch.  The two plots have equivalent genetic potential.  One plot received fertilizer (an environmental condition), the other pot receives no fertilizer.  The average height (i.e. intelligence) differences between each pot will be due to environmental differences (fertilizer), however the height differences amongst individual plants within a pot are due to genetic differences (assuming similar conditions throughout the pot). There is debate about whether heritability estimates even matter, since they can't be applied to an individual or be used to help people:

Wahlsten (1997, p. 84) states that:

"It does not matter whether the field of human behavior genetics finally decides that the heritability of IQ in the United States is 25%, 40%, 50%, or 70%. Any such estimate will be utterly useless to anyone seeking better ways to improve the intelligence of the nation through health care and education."

Intelligence & socioeconomic status

Herrstein and Murray (1994) argue that low intelligence causes low SES, rather than the other way around. So, according to these authors, while SES is correlated with IQ, it should be considered a consequence rather than a cause.

However, adoption studies seem to indicate that SES has a strong, causal effect on intelligence, e.g.: "Well-controlled adoption studies done in France have found that transferring an infant from a family having low socio-economic status (SES) to a home where parents have high SES improves childhood IQ scores by 12 to 16 points or about one standard deviation, which is considered a large effect size in psychological research." Wahlsten (1997, p. 76). Several recent US studies have demonstrated improvements in children's IQ's by improving the lives of infants in disadvantaged circumstances. These studies employed random assignment of children and families to treatment and control conditions.

These studies selected families with: • low parental IQ • low parental education • minimal financial resources

Experimental group received:

• Enriched, educational day care outside the home every weekday from 3 months to start of schooling Control group received: • nutritional supplements and pediatric medical care or crisis intervention but no educational day care Even though the children returned to their home environment every day and spent holidays and weekends with their families (mostly unemployed, single mothers) in poverty-stricken neighborhoods, there were large gains in IQ; almost as much as in the French studies previously mentioned.

Furthermore, the mean IQ of the enriched groups appeared to be quite typical of healthy American children. These children continued to show higher IQ scores than controls at age 12 (Wahlsten, 1997). Of course, in these American studies, SES and education were being manipulated. There is of course a strong correlation between SES and education in both directions.

Intelligence & education:

A number of studies have shown that schooling and intelligence influence each other. Higher intelligence tends to lead to prolonged schooling and longer schooling leads to higher IQ.

Intelligence at age 5 predicts better than any other variable a child's future educational progress and attainment (Kline, 1991).

Wahlsten (1997): • delays in schooling cause IQ to 'drop' 5 points per year • temporary drop in IQ during school vacations

Winship & Korenman (1997):

• 2.7 IQ point advantage for each year of schooling • thus to predict later IQ, two estimates are useful: early IQ estimates and number of years of schooling

A study by Cahan and Cohen, found that older children in a grade tended to score slightly higher than their younger classmates but importantly they found that children who are in a higher grade but are virtually the same age as children in the grade lower have higher IQ scores. It is postulated this is due to the extra year of schooling. However a number of authorities believe that enriched or increased schooling has little effect on intelligence and have refute the suggestion that intelligence can be modified.

"Compensatory education has been tried and it apparently has failed." - Jensen, 1969

Herrstein & Murray (1994), p.389:

One justifiable criticism leveled at educational enrichment studies conclusions about increased IQ are that what is being modified is performance on a test rather than an actual modification in intelligence. Children in enrichment programme often receive extensive instruction and practice in test taking. “What has been temporarily modified in the early stages of early intervention programme is performance on a test, not the child’s general intelligence” (Herman Spitz, 1999, p. 289).

This would account for the well-known fade-out effect, whereby initial, often very high gains in IQ scores, in experimental “enriched schooling” groups, return to the level of the control group a few years after the “experiment”.

In the US a large nationwide programme, the Head Start programme, aims to enrich the schooling of disadvantaged children. On the whole, the results have been mixed. Head Start and programme like it have been criticized for not living up to expectations in changing IQ.

Head Start type programme have also been criticized for not effecting last changes. This is not surprising if children return to poor, unsupportive, deprived environments. And, in fact, such a finding supports the idea that IQ is malleable - in both directions.

New and better ways of educating, improving, and maximizing individual potentials in intelligence are likely to be developed. As this happens, more and more of the environmentally influenced variation in IQ is likely to come under control and estimates of the 'environment' proportion could increase.   Intelligence & occupation:

"In more than 10,000 studies the average correlation of IQ with occupational success was 0.3...this correlation is certainly a low estimate of its true size...no other variable, either of ability or personality, can approach this figure." - Kline (1991), p. 139

Herrstein and Murray estimate the relationship between IQ and occupation to be between .2 and .6 (i.e. that IQ explains between 4% and 36% of the variations in occupation). These correlations are slightly higher for skilled, professional jobs, and slightly lower for jobs that require less skill. Whilst this might be useful in describing groups, it means there is questionable value in administering an IQ test to an individual in an attempt to help determine their occupational options. It may be a useful approach, however, to help select the best 100 employees from a 1000 applicants (Howe,1997, p.97).

Comments on the scope & quality of intelligence research:   All this research uses psychometric, quantitative tests of intelligence, which we know from previous lectures corresponds somewhat (but not entirely) with our conceptions of what intelligence is.

Multiple intelligences or subcomponents of intelligence are barely considered in much of this research. Neither are alternative measures of intelligence, such as speed of processing, evoked potentials, or practical intelligence, etc. Future research on brain-behaviour connections will probably help to more accurately isolate the functions of 'intelligence' (Weinberg, 1989). In addition, as we come to understand and develop more effective environmental interventions to maximise individuals' IQs, this will possibly expand the relative important of the 'nurture' component. Nevertheless, there remains the spectre of eugenics - those who would argue for selective breeding on the basis of intellectual ability. This issue is likely to rear its head again in the future and with new genetic technologies could appear in a more dynamic form.   The role of “interaction": An under researched area, while the nature vs. nurture debate has raged, is the contribution of interactions between genetics and environment on IQ variance. In the over focus on nature vs. nurture issues, the attempts to estimate the relative contribution rests on the somewhat naive notion that there is a constant, true value. In reality, "gene expression is environment dependent" and it impossible to obtain pure estimates of genetic vs. environmental contribution - one could not exist without the other. The environment a child experiences is partly a consequence of the child’s genes as well as external factors. To some extent a person seeks out and creates his or her environment. If she is of a mechanical bent she practices mechanical skills; if a bookworm, she seeks out books. Thus genes may create an appetite rather than an aptitude. Remember that the high heritability of shortsightedness is accounted for not just by the heritability of a gene for short sightedness but also by the heritability of literate habits. Thus, a future area for research which blends those in the nature camps with those in the nurture camps would be examine which environmental components allow people to optimally realise their genetic potentials for a variety of areas of cognitive performance (e.g. see Feldman, 1986).

What have we learnt about intelligence:

So, what can we say about nature vs. nurture as causal determinants of intelligence? A conservative, seemly safe position is that: "In the field of intelligence, there are three facts about the transmission of intelligence that virtually everyone seems to accept:

1. Both heredity and environment contribute to intelligence. 2. Heredity and environment interact in various ways. 3. Extremely poor as well as highly enriched environments can interfere with the realization of a person's intelligence, regardless of the person's heredity” (Sternberg & Grigorenko, 1997, p.xi). 4. Although most would accept a causal role of genetics, the exact genetic link and how it operates is very far from being understood - another point that most psychologists would agree on. It is certainly not a single gene, but a complex combination of smaller genetic markers. 5. But likewise, it is difficult to pin-down single, identifiable elements of the environment, which directly influence IQ scores. So what have we learned about intelligence: that it’s difficult to define but that there is SOMETHING we call intelligence that appears to relate to ability to reason abstractly, to learn and to adapt. That we can measure some part of it, although poorly; that it’s partially caused by genetics, partially be environment; that the real causes are the complex, not well understood interplay between genetics and environment; that it is somewhat though not greatly modifiable; that sometimes what we learn from tests is used inappropriately but that IQ tests can be useful in helping children attain their potential.

Final quotes:

"Measures of intelligence have reliable statistical relationships with important social phenomena, but they are a limited tool for deciding what to make of any given individual. Repeat it we must, for one of the problems of writing about intelligence is how to remind readers often enough how little an IQ score tells you about whether the human being next to you is someone whom you will admire or cherish." Herrnstein and Murray (1994, p. 21)

"Mother Nature has plainly not entrusted the determination of our intellectual capacities to the blind fate of a gene or genes; she gave us parents, learning, language, culture and education to program ourselves with." (Ridley, 1999, p. 77) THE CONTROVERSY OF NATURE AND NURTURE

Are we the way we are because of our genes? How much of our personality and characteristics are because of the way we were brought up, and our experiences, and how much is because of the way we were wired when we were born? The argument of nature, our genetics, and nurture, our upbringing, has been going on for years, and scientists are still struggling to find out why we are whom we are. If you asked 100 randomly selected genetic scientists their view on the controversy of nature vs. nurture, you would get 100 entirely different answers, and almost every one would make perfect sense with the evidence that supports it. As Kenneth Rothman said, "It is easy to show that 100 percent of any disease is environmentally caused, and 100 percent is inherited as well." Thus, it is a heated debate that has been going on for decades, one that may never stop. (N vs. N; an Unnecessary Debate) In February 1999, we completed the Human Genome project. Since then, scientists have been looking for new clues in our DNA, trying to find hints of certain genes and what they mean, and what that means for human society. Most scientists base their conclusions about nature and nurture by studying identical twins that were separated at birth. These twin sets tell us many things about nature vs. nurture. We can compare how they acted in different environments, see how many things they did that were surprisingly alike, how they score on IQ tests, if they answer many of the questions the same way, and how similar their health records are. (Farber, 4) One living example of the idea that your genes say much about who you are the Lewis and Springer Twins. When they were born, they were both adopted into different families. They first met when they were forty years old, and they then found that the similarities between them were extraordinary. Both were named Jim, both got dogs and named them "Toy," they had the same hobbies, jobs, handwriting, weight, appearance, and test results. Because of this, and other similar cases, some scientists believe that genes are the dominant force in creating who we are. (Farber, 33) Some scientists however, think that our genes have very little to do with the specific things that we do. Scientists started thinking this more when we first finished the human genome and discovered that we only had 30,000 genes. Until we finished the genome, we thought there could be genes for nearly all of our characteristics, but when we learned we only had 30,000 genes we decided that was not enough genes to have that many different genetic characteristics. (Clark, 102) One of the main questions that has been asked is, "Does Genetics influence intelligence?" Could social Darwinism, the belief that some people are farther along in evolution than others and thus have social advantages, be alive in our society today? Some scientists say yes, while others say no way.

Francis Galton says, "Men who are gifted with high abilities... easily rise through all the obstacles caused by inferiority of social rank." He believes that genetics has a great deal to do with intelligence. He argues that social advantages are not enough to make an average man great; however, social inferiorities are not enough to make a smart man "average."(Roleff, 25)

Walter Liepmann said, "Children of favoured classes test higher on the whole than other children." He argues that a child of a prominent person has a 1 out of 4 chance of becoming just as prominent, while an ordinary child has a 1 in 4,000 chance at becoming just as distinguished. (Roleff, 49)

The controversy between nature and nurture could affect each of us in many ways. One of the main ways it could change our lives would be if scientists found what triggers diseases like cancer. Also, from what scientists know now, we can say that many diseases like cancer are a mix of nature and nurture, and that if while we were still infants, we could take out the "nurture," then we would no longer be affected by those diseases. Such research could potentially have an incredibly large impact on our health and lifespan. (Clark, 35) I became interested in this subject last year when my class watched some videos on genetics and one of them mentioned this controversy. I chose it because it is a controversy that will rage on, and which we will no doubt continue to investigate.

The Identical Twins:

The original clones site stated that, “If the same person took an IQ test twice, on average it would show a 87% correlation. Identical twins reared apart have a 76% correlation in IQ scores while fraternal twins reared together only had a 55% correlation” (Redden). This study suggests that intelligence is hereditable and even though your nurture may influence your ability to achieve a certain degree of intelligence, genes have a larger effect on how smart you are. This may partly be because people are born with certain abilities, and your nurture may try and force other interest or beliefs on you, but your true capabilities will override your nurturing. For example, if a set of identical twins are born with the ability to excel in science, but they may lack the ability to fully understand math and no matter how much practice they undergo they will never grasp the concept or have enough interest to become excellent at it. They may receive special tutoring or constantly study, but your hereditary ability largely impacts a person. In a research project conducted by the National Merit Twin study, they tested 850 sets of twins, 60% of which were identical. They concluded that, “Both Identical and fraternal twins are considerably less similar in personality and interest than they are in ability. General ability in identical twins was an 86% correlation, special abilities were a 74% correlation, Activities was a 64% correlation, Interest had a 53% correlation, and personality was a 50% correlation. The results for the fraternal twins are a 62% correlation for general ability, 52% correlation for special ability, 49% for activities, 27% correlation for interest, and 28% correlation for personality”(Osborne 20).

Many studies of twins reared apart have uncanny results. Take for instance, the twins named Jim from Twins Reared Apart by Susan Farber. The boy’s birth mother was only fourteen and immediately gave her identical twin boys up for adoption. The boys were separated when they were only four weeks old, and didn’t meet until 40 years after their birth. Even though two different families raised the twins, when they met they were the same height and weight, but even more surprising, they were both named Jim. Also, they both had dogs named Toy, they both took law enforcement training, they enjoyed the same hobbies, both of their first wives were named Linda, both of their second wives were named Betty, and they both named their first son, James Allan. Both men chain smoked Salem cigarettes, bit their fingernails, drove the same color and model Chevy, vacationed in the same spot, and excelled at math but struggled in spelling (33). This amazing story shows that nature played a huge part in the twin’s lives. Even though the same didn’t raise them family they had similar interest and attracted to the same things. The similarities in these men’s lives were more than coincidental. This isn’t the only study of twins separated that have shocking characteristics, Twins Reared Apart by Susan Farber, describes another set of twins, Edwin and Fred who were separated at infancy and met at age 26. Upon meeting they realized they both were electricians, and they were married at the same time to similar types of women. They both had four-year-old sons and fox terriers named Trixie. When growing up, both boys often told playmates that they had a brother who died. (33-34). The boys telling people they had a dead brother symbolized that they felt something missing in their lives; they must have sensed that they use to have something that is no longer there. Maybe this goes back to the baby’s connection in the womb. Identical twins share an egg so they may have more of a connection than fraternal twins who have two separate eggs. ““Environment” begins as soon as the egg is fertilized, It is possible that the environment within the womb may have a decisive, and, in some instances, a more decisive influence than the world into which the neonate emerges at birth” (Farber 13). So, maybe when the twins were separated they knew that they once had something that is now missing. Burlingham suggest that, “Identical twins, when they grow up, often fail to develop into two separate human beings. It remains a matter of conjecture whether this is due to the twinship itself, o