I am fascinated by the topic of nature vs. nurture. How much of who we are is controlled by our genes and how much from our environment. I have found that many adoptive parents and parents through donor sperm, donor egg, or donor gametes share my interest. What is the importance of genetics in determining who we are?
One of the best ways to study the relative influence of genetics and environment is through twin studies, and one of the best of the best study of twins was a meta-analysis of all the twin studies published in the last 50 years. In total they looked at 17,804 traits over 14 million twin pairs across 39 different countries. Unbelievable!! This is truly a phenomenal feat.
As the lead researcher said, we used to give ranges about how much a specific trait was controlled by genes—now we know and have a specific percentage!
HUGE Study of Importance of Genetics in Determining Who We Are
It’s impossible to have a quick summary of a study as vast as this, but if you must have a bottom line it is this: genes and environment are about equally as influential in how we (or our children) turn out. However, the influence of nature and nurture is a complex interplay rather than a simple either/or and is far from equal across all traits and diseases.
If you have any interest beyond this quick and dirty summary, I can’t recommend enough this Creating a Family show where I interviewed one of the authors, Dr. Danielle Posthuma, Head of Department of Complex Trait Genetics at the Center for Neurogenomics and Cognitive Research at the Neuroscience Campus in Amsterdam, The Netherlands.
Genes are Not Predestination
It’s easy to read this report, especially with the traits that are heavily influenced by genetics, and worry that our genetic history will determine our fate. We get only half our genes from one parent, so even if a trait was 100% influenced by genes, the offspring would still only have a 50% chance of having this trait, and few traits are even close to 100% controlled by genes.
The Details That Matter to Most of Us
The general 50/50 summary is not all that helpful to those of us wanting to look at specific traits for us personally or for our kids, so I specifically asked about the traits that we get the most questions on from pre and post-adoptive families and from donor conception families.
The percentage given is the genetic influence on the trait or disorder—i.e. how much genes play a role in a person having this trait or disorder. Environmental factors make up the rest of the risk.
- Depression-34 % genetics
- Anxiety disorder- 40%
- Alcohol 41%
- Cocaine- 64%
- Opiates- 32% (males only and few studies (18) therefore not as reliable)
- Sedatives – 63%
- Tobacco- 44%
- Conduct disorder (antisocial behaviors, behavioral issues, violence, etc.) 49%
- Hyperkinetic disorder (includes ADHD)-68%
- Intelligence-average of all ages 51%. Genetic influence increases with age, and for adults, it is 62%.
- Mild mental retardation 19%
- Height-80% for height at adulthood.
- Cancer risk-most twin studies analyzed did not focus on specific diseases -46%
- Breast cancer- 56% (only 7 studies)
- Cardiovascular issues- most twin studies analyzed did not focus on specific diseases- 29%
- Looking after oneself- activity level, self-rated health, subjective well being-41%
- Personality, neuroticism, self-esteem- 44%
- Reproductive problems-structure and function 31%
- Longevity/age at death/mortality- 47%
- Alzheimer- 63%
- Cleft lip-98%
The power in this study for parents is that if we have information on our children’s genetics, we can assess whether they are predisposed to this trait or disorder, and can take action to change their environment to make it less likely that this will happen.
The more scientifically minded of you might enjoy playing around on the new interactive website the study authors have launched, MaTCH.
Does this information give you peace or make you more anxious? Would it be helpful for you when deciding on an adoption match or choosing a donor?
Other Creating a Family Resources You Will Enjoy:
- Nature, Nurture, Genetics, and Environment
- Ethical Issues in Genetic Testing in Adoption
- What Happens in an Embryology Lab and Why Patients Should Care
First published in 2015; Updated 2018
Image credit: jenny mae