Nature vs Nurture

Anthony G Benoit  abenoit@trcc.commnet.edu
Revised

On June 26^th, 2002, with British Prime Minister Tony Blair by his side, President Clinton announced that the human genome had been sequenced by a public consortium, the Human Genome Project, and a private company, Celera Genomics. In February 2001, the American journal Science and the British journal Nature published drafts of the genome. While some were amazed that the human organism could be described by a mere 30,000 genes (only twice as many as in a fruit fly), others saw that publication as heralding a new age in the treatment of illness and foretelling the solution to a riddle that has plagued intro psych students for generations: Is human behavior and character caused by in-born factors or environmental influences?

Richard Fulkerson calls our attention to a line from the 17^th century, "Nature makes the boy toward, nurture sees him forward" (Richard Mulcaster) and from Shakespeare, "A devil, a born devil, on whose nature / Nurture can never stick" (The Tempest). But it was Galton (Darwin's cousin) who called this question the "nature vs nurture" debate.

For example, what causes:

• Differences in intelligence
• A tendency toward violent behavior
• Sexual preference
• Heart disease
• Schizophrenia

Studies of these and other characteristics typically reveal no simple cause, even for things that run in families.

Over the last century or so, different scholars have emphasized different causes of behavior.

• Behaviorists, such as Watson and Skinner, believed that each organism is a tabula rasa (blank slate) on which experience writes.
• Skinner primarily studied rats and pigeons, but also examined primates and other species. He concluded that the principles of operant conditioning were the same across species. He was right in the sense that most vertebrate and some invertebrate animals have the ability to be conditioned. But, the parameters of that conditioning vary greatly from species to species and even within species.
• Ethologists, who are biologists who study behavior, have long known of species-specific behaviors and fixed-action patterns. These are sets of behaviors, often quite complex, that an organism doesn’t have to learn and which vary little among individuals of the same species.
• Even humans show these: For example, we all smile when we are happy, even blind children who have never seen a smile.
• Tooby and Cosmides have described a "Standard Social Science Model" in which all potential human behavior is equally possible (biologically) and in which experience, upbringing, and culture determining which behaviors actually occur.
• Note that they argued that this model is not correct: An infant who must learn everything from scratch is at a disadvantage over one prewired to learn what is important.
• In 1975 Edward O Wilson, an entomologist, published Sociobiology in which he proposed that social behavior has a biological basis, even in humans.

What are we contrasting?

• To study the influence of genes on personality and behavior, psychologists have carried out:
• Twin studies-genetically identical individuals are compared with each other and with those who are genetically different.
• Adoption studies-people who are genetically different but raised in the same environment are compared.
• Marker studies-versions of specific genes are compared in people with certain traits
• Some have made the mistake of looking for racial differences in psychological characteristics, such as intelligence. Any such differences are not evidence of a genetic basis, since there is essentially no average genetic differences between members of different races. (In fact, all people share about 99.9% of genes--that's why we can talk about the human genome.) Race seems to be a cultural or social concept, not biological.

The findings of these studies are summarized by Turkheimer's three laws.

Why ask?

• One could argue that the answer has ethical implications. Certainly criminals have claimed to be less guilty since they were the victims of a crummy upbringing.
• Both the genetic and cultural point of view have been used to justify horrible social practices.
• The Khmer Rouge killed millions based on the belief that these people represented undesirable cultural influences.
• The Nazis killed millions to remove supposed undesirable genetic influences.
• The question helps us to generate hypotheses and refine theories.
• Science tries to supply the most accurate information and models to guide policy decisions or simply amuse and enlighten.

Often missed in the debate is that uniformity or individuality tells us little in itself about the origin of a trait.

• When the newspapers claim that a genetic cause for mental illness has been found, the story usually centers on the finding of genetic differences that correlate with abnormal psychological conditions.
• But, what about things that are true of all or none of us? Breathing is universal, and it has a genetic cause. Wearing clothes is also universal, but not genetic. What about language?
• Behavioral geneticists, who carry out twin studies and the other techniques described in Myers, are interested in how much variation in traits can be explained by genetic variation, also known as the heritability of the traits.
• In the case of disease, understanding a genetic basis can assist in developing therapies.
• Evolutionary psychologists, on the other hand, typically are not interested in variable traits. Rather, they look at things we don’t inherit specifically from our own parents but from our ancestors as a whole. (Note: Most genes are the same in everybody.)

What do genes do?

• Each individual starts as a single cell containing a set of genes. Genes come in pairs, and one member of each pair comes from each parent.

• A gene contains the recipe for a protein. Proteins are the chemical tools of every cell. They do what needs to be done. The chemical environment inside the cell is controlled by what proteins are present. In turn the chemicals in the cell control what genes are active at what times.

• The cell divides, at first forming seeming identical copies. Later, the dividing cells start to look and act differently.
• The presence of different genes causes the differentiation to proceed differently (if you knew how, you would win at least one Nobel prize).
• Humans have about 30,000 genes that are grouped into 24 pairs of chromosomes. Thus, we each have two copies of each gene, which can be the same or different.
• One chromosome in each pair comes from each parent.
• Identical twins develop from the same individual cell, and are thus genetically identical.

• Some spectacularly bad political movements have been based on an ignorant overconfidence in the power of genes:

• eugenics (early 20th century)
• Nazism
• social Darwinism (19th century)

Development

• Biological development is a set of processes that follow a genetic plan.

• The environment in which development occurs is subject to many non-genetic influences, though it is also partly under genetic control.
• The expression of genes is greatly influenced by environment, but also partly under genetic control.

• Psychological development has been described from a number of psychological perspectives.

• Freud, Piaget, Erikson, Kohlberg
• The N/N question might be reframed as a question about the extent to which psychological development is outside of biological control.

Learning

• Watson and Skinner
• Failures of learning theory:
• Behaviorism has had to admit that not all species are the same
• Political movements have overestimated human flexibility:
• Communism
• Free love

Nature? Nurture? Yes!

• A number of scientists, such as Frans de Waal and Henry Plotkin, have proposed that the question should be abandoned, or at least modified.
• de Waal recalls Hans Kummer's analogy:
• When we hear drumming, does it make sense ask whether the sound is caused by the person hitting the drum or by the drum itself?
• If the sound were to change, we could investigate how much of the change was due to a change in the drum and how much to a change in the drummer.
• Consider language: Is language an innate ability in humans?
• What do we mean by "innate"?
• Language is like many other types of behaviors in that it requires an interaction of environment (parents, etc) with intrinsic factors within the developing brain (or mind) of an infant.
• An oversimplification contrasts innate theories with learning theories.
• The pure Skinnerian approach was long ago discredited, though there may be some operant conditioning at work: if children are reinforced for speaking correctly, the frequency of correct speech might therefore increase. Presumably there would be some shaping involved.
• Children who are spoken to more, do speak more at an earlier age, but there is a big frame problem here: what is the controlling stimulus?
• Steven Pinker put it the innatist view bluntly: "People know how to talk in more or less the sense that spiders know how to spin webs."
• There is still some resistance to this point of view.
• To me, much of the controversy boils down to a disagreement over how much of language knowledge is acquired from the environment and how much is innately available to the developing brain.
• Clearly both environmental input and a developing human child are required for normal speech to come about.

Influence of Life Stress on Depression: Moderation by a Polymorphism in the 5-HTT Gene (Caspi, et al., 2003, Science 301:386-389)

• Depression is a significant psychological disorder sometimes associated with stressful life events. The paper looked for a genetic vulnerability to this reaction.
• We know that drugs that affect serotonin reuptake can reduce the effects of depression.
• The 5-HTT gene has two forms, one called "short" and one called "long."
• People with either form show the same level of depression.
• When the experimenters looked at depression following major life stress, they found that those with the long form were not more likely to be depressed after a stressful event. Those with the short form were more likely to be depressed following one or more stresses. The more stresses they had, the more likely they were to be depressed.