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 intellectual disability 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?[sws_green_box box_size=”515″]
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
Add Your Comment
I was totally enthralled listening to the podcast. I “rewound” several times to get the number she said. I am a little bit of a research enthusiast as well, especially when it comes to nature/nurture. (Don’t get me started on the Manning football dynasty at a dinner party!)
I think information is powerful, knowing what we can possibly expect based on heritability is good going in, especially in relation to substance abuse. However, I also believe in the power of arming our children with the knowledge that they have the power to make choices. Even if I am genetically predisposed to alcoholism the power to choose lies within me as well.
Thanks for sharing.
On the topic of this study I was interested in height being 80% influenced by genes. Wouldn’t the only way environment could influence height would be to retard the 100% influence by malnutrition or leg binding or wearing a corset during pregnancy?
I wonder if a lot of this epigenics craze is based on the possibility that someone could retard or derail the person’s natural trajectory by how they behave during their pregnancy or by how they behave while raising their child (or someone else’s child).
I am responding to the question about whether or not I think children in families who have struggled with infertility are more cherished than other children.
After 10 years of coping with unexplained infertility (3 rounds of IUI, 2 IVF cycles (both of which resulted in miscarriage), and 3 years of domestic adoption approval with no placement, my husband and I started foster care training. Several months later, an amazing 2.5 year old little girl was placed with us for foster care. A year and half after that, we got to adopt her! Do we cherish her? ABSOLUTELY! Do our extended family members cherish her? ABSOLUTELY! In fact, we know that sometimes we are overly attentive, watching every single thing she does and centering every life activity around her. This became glaringly apparent when we stayed with friends at the beach for a weekend. We all sat down to dinner. Our friends’ children ate and talked to one another, occasionally speaking to the adults. Our child wanted everyone to be quiet so she could sing a song for them. They obliged her. Next, she interrupted the adult conversation to ask silly questions. In her defense, she knows no different. At dinner time, it is all about her. In fact, almost any time of day, it is all about her. We are working on this and getting better. I tell this story to segue to my best guess at what the answer to your question might be. I feel certain that almost all parents cherish their children, whether the child was conceived by accident, on the first try, using assistance, or adopted. However, I suspect that those of us who had to work harder and wait longer to make it happen may be more in awe that this child/ren is finally here! With that awe may come a heightened level of attention, concern for safety, etc. Does this mean that we cherish our child more than other parents do? I do not think so. I just think it means that, in some ways, we think about parenthood from a different perspective. In most cases, when things come easily, we appreciate and enjoy them, but maybe do not wake up each morning feeling intense gratitude for them. After almost two years, I wake up each morning still in awe and intensely grateful that our little girl is there. I would cherish her none the less if she had been conceived the day we started trying, but I doubt that my awe and gratitude would be the same. Of course, everyone is different, and I can only speak from my personal experience.