Recently, I’ve found myself citing the nature versus nurture debate in a few of my comments on others’ blog posts. So, I decided maybe it would be worth looking in to. After some light research I think it could turn out to be a decently interesting blog post… or at least I’ll have fun researching it! As one of the oldest and highly studied issues in the realm of psychology there is sure to be a myriad of studies exploring the issue.

So, what is this nature vs nurture thing?

To start, we need to understand what psychologists mean by nurture and nature. An informational page for a Sociology class given at UC Santa Barbara explains, “Nature refers to all the evolutionary factors that have shaped the genetics that we have inherited from our parents and ancestors.” Additionally, the page defines nurtures as, “…all the things that have influenced us since we began to develop (from the moment we were conceived).” The nature vs. nurture debate stems from the issue of trying to determine which, nature or nurture, has a greater influence on human behavior and ultimately, who we are as people. A greater understanding of how these two things influence human development could potentially help psychologists better understand they way they approach psychology.

Where is the debate now? The Twin Study – May 2015

For a long time, psychologists have used identical and fraternal twins alike to study the nature vs. nurture issue. In a study recently published in the journal Nature Genetics, researchers from the Queensland Brain Institute and the University of Amsterdam conducted a meta-analysis of studies done on over 14 million twin pairs from January 1900 to December 2012 across 39 different countries. When identifying relevant studies, the researchers ran 2 different searches on PubMed which yielded a whopping 4,388 studies; after they eliminated irrelevant or unquantifiable studies they were still left with 2,748 studies of which they were able to receive the full text for 2,743 of the 2,748 (99.8%). They also controlled for bias due to their belief that studies with extraordinary results would be more likely to be published that those with “modest results.” Finally, before analyzing these studies, they classified the traits of the twins using a the World Health Organization’s (WHO) ICF classification tool. They meta-analysis returned some pretty interesting results. The researchers reported that heritability and genetics accounted for 49% of the majority of  traits analyzed (69%), leaving the other 51% of to be determined by the environment. These findings created some pretty big ripples in the world of psychology. In articles such as this, journalists use the results to support their claim that the debate was over and that nature and nurture both play an equal role in human development. However, we have to be careful interpreting these results. Of course, they are astonishing in the respect that nature and nurture both seem to hold equal weight in determining our traits but 31% or traits studied in the meta-analysis did not exhibit this 49/51 relationship. Additionally, as we learned in class, meta-analyses have a tendency to be affected by the file drawer problem. Though it does seem the researchers did an adequate job of eliminating bias in the studies PubMed brought back to them, there is a chance that there are a significant number of studies that were not published due to their modest results. All else aside, this is the most comprehensive and well known study that explores this Nature vs. Nurture debate. After reading what was published in Nature Genetics I found myself struggling to find things wrong with this study and for the time being, these are the most comprehensive and definitive results.

Genetics and IQ

IQ has long been believed to be very closely related to genetics. I remember learning in myhigh school AP psychology class that genetics are the main indicator with respect to intelligence. In the spirit of SC 200, I decided to figure this one out for myself as well. After a few different google searches I found two studies published in Nature 8 years apart (study 1, study 2) that both support that intelligence is highly inheritable. Even more interesting, in the second study, the tendency for people mate with others who share similar genotypes/phenotypes (assortative mating) affects the genetic transfer of intelligence because people mate with others of the same intelligence. Here is a short video narrated by Morgan Freeman that discusses intelligence in respect to the nature vs. debate. Who doesn’t love Morgan Freeman?

What does this all mean?

For now it seems that the psychology community has settled on the fact that nature and nurture both share an equal role in human development in behavior. Now, it seems that it is now “nature nurture” instead of the previously accepted “nature vs. nurture.” However, the story seems to be different when we look at genetics and intelligence. Perhaps a meta-analysis of studies that assess intelligence and genetics could shed some more light on this. Overall, a basic knowledge of this debate is important even when asking scientific questions that relate to human behavior and the way things are. The twin study demonstrates the importance of examining the environmental effects as well as the effects of genetics on human centric scientific questions.