Intelligence: Nature or Nurture?

Intelligence: Nature or Nurture?

This controversy is between eugenicists and euthenists...

This is a very complex debate...

How is this topic studied?

Like the behavior genetics perspective!

Emphasizes the ways in which the environment influences our genetic predispositions

Eugenicists are...

Twins!

For example:

A lot of parenting advice/research assumes a relationship between parents’ actions and the development of their child that doesn’t exist. A child that is physically abused might grow up to be violent because of a gene that is passed down, not solely because of their experiences in youth.

Euthenists are...

It is difficult to differentiate between the impacts of heredity and environment, as each could affect the other

Adopted Children

IQ tests are the generally accepted measure of intelligence, but some contend that it can't be accurately quantified

Cases of identical twins (monozygotic) are the only way to compare two individuals with the same genes and a very similar environment

...other than cloning

Adopted siblings are the best way to compare individuals that have different genes and grow up varying environments

People who believe human nature and intelligence are biologically determined (Strickland, 2001)

People who contend that, given a positive and enriching environment, most individuals have the potential for high levels of development (Strickland, 2001)

In the case of twins, comparing who they grow up to be when separated at birth isolates the genetic variable

Cases of fraternal twins (dizygotic) are useful because those individuals grow up in the same environment, but have different genes (The genes of fraternal twins and normal siblings vary equally)

In the case of adopted siblings, you can isolate the environmental variable

How does Heredity impact intelligence?

How does the ENVIRONMENT impact intelligence?

CONCLUSION

Alan S. Kaufman is a famous Psychologist known for his study of intelligence testing

ex. someone who is more intelligent might ask more questions and have smarter friends, ultimately enhancing their intelligence

He observes that scientists who argue in favor of genetic determination of IQ cite these data to support their assertion that:

• Monozygotic twins' IQs are more similar than those of dizygotic twins
• IQs of siblings correlate more highly than IQs of half-siblings, which, in turn, correlate higher than IQs of cousins
• IQ correlations between a biological parent and child living together are higher than those between an adoptive parent and child living together

As children grow older, their scores differ more and more from their adoptive family (McGue, 1993), and grow more similar to their biological family

McGue 1993...

Various memory and intelligence tests were performed on identical twins over time to compare the impact of age

Social learning theorists refer to another layer of complexity in the relationship between environment and human behavior: the self-generated environment. This concept refers to the fact that a certain behavior or behaviors may produce environmental conditions that can affect future behavior

Fraternal twins who are treated more similarly than regular siblings (because of shared age) have closer results than the siblings (Myers, 2012, 2)

Even though I have learned that genetics play the most significant role in determining intelligence, I have also learned that intelligence is very much in our control. From this research as well as experience I know that changing my surroundings has a dramatic impact on who I become. By asking more questions in classes that I struggle in, I will build habits that allow for future growth. When I go to college I will do my best to make friends that resemble who I want to be, because I know the influence that they will have. I can't change my genes, but altering my environment can be very beneficial.

Nancy L. Segal examines virtual twins—genetically unrelated siblings (typically adopted) of the same age who were reared together from early infancy—to assess environmental influences on intelligence.

“I expected the virtual twins to be more alike than they were because they had been raised together all their lives, yet they were so much less alike. It gives us another piece of evidence in the whole nature-versus-nurture puzzle.”

- Segal

Dr. Segal’s research typically involves interviewing virtual twins when they are at least 4 years old, giving them intelligence tests and having their parents and teachers fill out extensive questionnaires on behavior, their relationship with their sibling and their school, medical and dental histories. So far she has conducted follow-up interviews with 42 of the 137 pairs

The results of her studies reveal that the IQ correlation of virtual twins fell considerably below correlations reported for monozygotic twins, dizygotic twins, and full siblings.

(Strickland, 2001)

Segal interprets these results as a demonstration of the modest effects of environment on intellectual development and as supporting a predominantly genetic role in determining intelligence.

Based on this research, it is clear that genetics have more influence on intelligence than environmental factors.

In general:

In cases of siblings separated at birth, the child is always more similar to their biological family than their adoptive one. In studies of fraternal and identical twins, the identical twins are always more similar than the fraternal twins.

Though it is found that intelligence and behavior improve as one's surroundings improve, the changes aren't as significant as those due to heredity.

The determinist view emphasizes the adaptation of people to their surroundings, and considers behavior largely as a function of those surroundings (Strickland, 2001)

Correlation in Verbal Ability Scores

(Myers, 2012)

Here is a crazy example...

• With time, adopted children and their biological family grow more similar than any other category
• With time, children and their birth parents grow more similar
• With time, adopted children and their adopted family grow less similar

WOW!

ex. A pair of identical twins was separated at birth. One twin was raised in a Nazi home, the other was raised in a Jewish home. When they walked into the lab for testing, they were wearing identical shirts, both liked to dip buttered toast in coffee, both kept rubber bands around their wrists, both flushed the toilet before and after use, and both sneezed in crowded elevators so that they could watch the people jump.

Kaufman asserts that the following results support scientists who believe that environment more strongly determines IQ:

• IQs of dizygotic twins correlate more highly than IQs of siblings of different ages despite the same degree of genetic similarity
• Unrelated siblings reared together, such as biological and adopted children, have IQs that are more similar than biological siblings reared apart
• Correlations between IQs of an adoptive parent and a child living together are similar to correlations of a biological parent and a child living apart
• Siblings reared together have IQs that are more similar than siblings reared apart, and the same finding holds for parents and children, when they live together or apart

Identical twins’ scores become more similar with time (Deary, 2009; Plomin, 1997)

The Neuroscience perspective:

Intelligence test scores improve as kids are adopted into better homes (Myers, 2012, 2)

Behavior is a result of brain structure and function. Changes to the brain mean changes to behavior.

The blank slate idea states that everyone is born the same, and that our experiences mold who we become (Pinker, 2003)

The way in which our brain functions is a result of our genes. This theory supports the idea that intelligence is determined by heredity.

Segal, Herrnstein, Murray

In their 1994 book The Bell Curve, Herrnstein and Murray expressed their beliefs that between 40% and 80% of intelligence is determined by genetics

Steven Pinker: Human nature and the blank slate

Steven Pinker's book The Blank Slate argues that all humans are born with some innate traits. Here, Pinker talks about his thesis, and why some people found it incredibly upsetting.

This talk discusses many aspects of the nature vs. nurture argument. Pinker supports his argument that everyone is born with equal potential and that our experiences mold us. This is the blank slate idea. He also provides examples of the impact of genetic and environmental factors when he describes studies on twins. He provides interesting facts and diverse information that make this a very entertaining and informative video.