Twins And Genetic Adoption Studies

In the nature versus nurture debate, researchers often turn to twin and adoption studies to measure the influence of genetics and environment on individuals. By studying twins who were raised both apart and in the same household and by looking at individuals who were adopted, scientists can gain better insight into the nature vs. nurture theory.

Nature vs. Nurture Defined

In the nature versus nurture debate, the term “nature” refers to the genes we inherit while the term “nurture” refers to our outside environment.

The Nature vs. Nurture Debate

For hundreds of years, the scientific community has been seeking to answer whether our genes or the environments in which we are raised have a greater influence on our development.

Some researchers think the genes we inherit from our parents play a strong role in guiding our development. Others, however, think our environment has a stronger role in shaping who we will eventually become. Of course, many believe that both environment and genetics play a strong role in our development.

When people talk about nature versus nurture, they aren’t talking about our physical traits. Scientists know that the color of our eyes, skin and hair is determined by our DNA. Rather, the nature versus nurture debate seeks to understand how a person develops his personality.

Twin and Adoption Studies

More than a century ago, English scientist Sir Francis Galton began to study how genetics influence intelligence. Galton theorized that children inherit their intelligence from their parents. Thus, he believed that genes were responsible for intelligence. In order to test his theory, Galton turned to twin studies.

Twin studies are invaluable to researchers interested in the nature vs. nurture debate. Identical twins have identical genetic compositions. Thus, by studying identical twins who were raised in different environments, scientists can see the impact of genes on development.

Also, scientists can study fraternal twins (twins who share only 50 percent of their genes) who were raised in the same environment to determine the impact that the outside environment has on the development of personality.

Modern twin studies have shown that almost all of a person’s traits are influenced, in part, by genetics. Some characteristics, such as height, are strongly influenced by genetics, while other traits, such as intelligence, are more likely to be affected by outside factors (class, family income, etc.).

Adoption studies can also help scientists determine the roles of nature and nurture in development. Children who are adopted share an environment with their siblings but do not share any genes with them. If adopted children share more characteristics with their adopted families than with their biological parents, a strong argument could be made for the influence of environment on development.

Results of Twin and Adoption Studies

Over the years, a number of twin studies have been conducted. One twin study, known as the Minnesota twin study, examined a set of identical twins that were raised in separate environments. Although the twins did not meet until they were almost 40, they shared many similar characteristics. The only explanation for the similarities was that the twins’ genes had strongly guided their development.

In fact, the Minnesota twin study led the researcher to conclude: “[On] multiple measures of personality and temperament, occupational and leisure-time interests and social attitudes, [identical] twins reared apart are about as similar as [identical] twins reared together.”

Interestingly, adoption studies have also shown the strong influence of genes (or nature). For instance, the Texas Adoption Project found “little similarity between adopted children and their siblings and greater similarity between adopted children and their biological parents.”

The Impact of Nurture

Though many twin and adoption studies show how genes impact a person’s development, it should not be assumed that a person’s environment (nurture) has no effect. In fact, the environment plays a large role in a person’s development.

For instance, a person with two obese parents might, in fact, be quite slender and healthy. This could be due to his access to healthy foods. Also, a person with two parents of less-than-average intelligence could have a higher-than-normal intelligence if he is raised in an environment where education is valued and where learning materials are made accessible.

The Debate Continues

Despite twin and adoption studies, researchers are still seeking to understand the extent to which genetics and the environment influence human development. While these studies often show us that while genes greatly determine who we are, they also show us that our environment plays a large role in our development.


AC Content Producer (December 16, 2005). The Childhood Nature vs. Nurture Debate Continues. Retrieved January 7, 2008, from the Associated Content Web site:

Bryner, Jeanna (July 19, 2006). Nature vs. Nurture: Mysteries of Individuality Unraveled. Retrieved January 7, 2008, from the LiveScience Web site: