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In 1940, two identical twin boys were adopted to separate families at 3 weeks old and would spend the next 39 years living completely separate lives with zero interaction. When they were finally reunited in 1979, what transpired was almost unbelievable. Both twins had married and divorced a woman named Linda and remarried a Betty. They shared interests in mechanical drawing and carpentry. Their favorite school subject had been math. Their least favorite spelling. They smoked the same brand of cigarettes and drank the same amount of alcohol and got headaches at the same time of day. They both vacationed on the same beach in Florida and both had a dog name they named Toy. I've seen this
story all over the internet and have obviously been skeptical. But after looking into it, it turns out they were real twins who were separated for 39 years and even participants in a landmark study called the Minnesota Study of Twins Reared apart published by a highly respected psychologist. And while many of the specific details lack hard proof, like the study doesn't actually mention the wise names or the dogs names, these were later published in newspapers and magazines that weren't necessarily verified. What we do know from the researches that their medical histories were almost identical, as well as their brainwave tests and personality tests, despite living completely separate lives, all to such a degree
that the study looked like it reported the same person twice. At the same time, mathematicians would argue that if you compare two people on a thousand different variables, like their favorite food, first car, name of first pet, cigarette brand, etc., the laws of probability suggest you will find at least five or six quote unquote impossible coincidences just by chance. So, were these twins so similar due to chance? Or was it because their genetics predetermined their lives? How much choice do you actually have in the outcomes of your life? Today, we're going to answer that question by looking at some of the most significant and wildest identical twin studies to help answer the question of nature versus
nurture, including one where NASA put one twin in space and realized his genetics changed compared to his twin on Earth. Another twin database that's given us breakthrough understandings of which diseases are caused by your environment versus which are actually genetic, how marijuana affects IQ, and how much your genes actually affect your lifespan. Like, will you make it to 100 years old? And then we'll touch on super recent research that asks the question, are you born smart? This research completely challenges our beliefs around school and intelligence and whether or not your genes or the school you go to play a more significant role. And finally, a study that looks at every
available twin study to answer exactly what percentage nature versus nurture play in our lives. Now, identical twins are such a great proxy for scientific research because they allow us to use the same set of genetics to see how different variables impact us. If you and I both love to run, we might be able to find some interesting correlations on how that affects our body and brain and long-term health. And that's super useful, but it could come down to genetic differences. Identical twins, on the other hand, allow us to see which parts of our lives are most defined by genetics, and on the other hand, which parts are most defined by our environments. It's for this reason that
twins are so revered in science, because they're possibly our best chance to understand the nature versus nurture question. So, first, let's take a look at what the Landmark Minnesota study found. Now you have to try and imagine a time when we didn't know that much about genetics. Like the prevailing view was that your upbringing and social environment were everything. Of course, we understood that genes encoded for things like the color of your eyes and affected your height. But the idea that your genes could also affect your personality or life outcomes as much as or even more than your environment was unheard of. And that's exactly what the Minnesota study found. By looking at
identical twins who were raised apart, they were able to see that how parents raised their child had little impact on personality traits like extraversion, neuroticism, or conscientiousness. Instead, these seemed highly heritable. If both twins were super anxious, it was more likely from their DNA than how their adoptive parents treated or raised them. Or put another way, even if one twin was put into a super calm and relaxed family, if they were genetically predisposed to be more anxious, then both twins were likely to be anxious regardless of their upbringing. But perhaps the most profound theory that the research proposed was that our genes
may actually drive us to seek out specific environments. A child with a genetic predisposition for music is more likely to seek out instruments and music lessons, effectively creating an environment suited to their genetics. So even if one twin was raised in an environment with little to no musical exposure, they were still likely to seek it out. Of course, the study wasn't finding the specific genes that do this, but it was showing that separated twins are statistically more likely to pursue similar interests and passions compared to two random strangers and even compared to two nonidentical siblings.
Really emphasizing how much of a role DNA plays in our desires and our choices. Many of these twins ended up with similar jobs, had similar religious views, and even small behavioral habits like how they would hold a cup of coffee were noted to be similar in the study between twins. Of course, the study never implied that your environment doesn't matter. Like, if you grew up in a musical family, not only are your genes impacting you, but your environment is reinforcing those natural desires. But this research was the first huge sort of shift in our understanding that our genes may actually have an impact on our behavior and ultimate choices. Now, since then, this research has continued to compile and reveal even
more shocking truths. The most famous database and research comes from the Swedish Twin Registry, which has nearly 200,000 twins in it, along with the Danish and Netherlands twin registries. One of the most cited papers in cancer research uses these databases. And they found that for the majority of cancers, it's actually your environment that plays a bigger role than your genetics. That means that it's not just a genetic lottery, but it's actually your lifestyle factors that most heavily influence cancer. Now, that may seem obvious when it comes to something like smoking and lung cancer, but it's true of things like stomach cancer and dietary choices we make, too. However,
they found a few specific cancers that do seem to have a major genetic component, which include prostate cancer with 42% heritability, colurectal cancer with 35% heritability, and breast cancer with 27% heritability. Another massive health finding was about dementia. Like if one twin gets it, what will happen to the other? Dementia is typically correlated with a shortened lifespan. And the research found that even if the second twin doesn't ever develop the disease, both twins have a similarly shortened life expectancy, which suggests that dementia isn't just a brain disease. It's more likely part of a bigger body system that affects health outcomes and lifespan in those prone to
it, even if they don't develop the disease from a cognitive perspective. Now, before these registries existed, it was believed that your lifespan was around 20 to 25% genetic. But now, we see it closer to 50%. Meaning that our bodies do sort of have an environmental clock going on. Yes, that still leaves room for 50% of your lifestyle to impact how long you live, but it's important to know that a good chunk of this is out of your hands and much more hardwired than previously thought. It also validates the search for longevity genes. And finally, does marijuana make you dumb? And I don't just mean in the moment while you're high. Because for a long time it was believed that marijuana use decreases IQ. But using these
registries, scientists were able to show that when one twin used weed and saw a drop in IQ, even if the other twin didn't, both pairs were likely to see that same drop in IQ. Now, that sounds weird, like one twin smoking is making the other one dumb, but what it means is that the decrease in IQ was likely related to some other pre-existing vulnerability or environmental factor and not necessarily the marijuana. The good old correlation doesn't mean causation. So, if somebody uses marijuana and their IQ lowers, it's more likely from another factor and just a coincidence and not a causal relationship. Marijuana is a perfect example of a topic that's been controversial for years. And just like all research, how it's covered in the
news can highly influence our perception and beliefs about it. But that problem is being tackled by today's sponsor, Ground News. An app and a website that gathers news from all around the world in one spot and not only shows you each publishers's political leanings, but gives a larger picture of how that news is being reported on more broadly. For example, this news on the reclassification of marijuana in the US has been covered by 456 news sources, and Ground News breaks this down further based on the political leanings of those sources. Not only can you get a summary of how the left, center, and right are covering this news, you can also read through different headlines and compare for yourself. For example, this right-wing headline highlights
frustration with the decision, whereas this left-leaning source shows it as a step in the right direction. You can even get an overall factuality rating for the coverage along with individual ratings for all the sources. But perhaps my favorite feature is their blind spot feed, which highlights stories that are not being covered by either the left or the right. The bias in these cases may just be that certain news outlets choose not to talk about particular topics. Now, we all have our biases and we can't just erase those, but I think ground news is a really great way to not only see the bigger picture of what's actually going on factually, but also get a sense of how other people around
you may be seeing the world. It's a step towards minimizing polarization and helping to have actually productive conversations. Because if you and I are seeing a completely different set of facts and perspectives highlighted, it may be impossible to have those conversations. You can check it all out at groundnews.com/asap or scan this QR code. By using our link, you'll be offered 40% off the unlimited Vantage plan, which is what I have. You checking out our sponsors actually does help us continue to make content. So, we appreciate it and want to thank Ground News for sponsoring the show. Now, before we get to one of the biggest questions around intelligence and if your school even matters, I want to look
at this really cool NASA twin study just because it's so fascinating. They followed and analyzed the biology of Scott Kelly while he was in space for an entire year and compared it to his brother, the retired astronaut Mark Kelly, here on Earth. They had like 10 different research teams that were studying molecular, psychological, cognitive changes to see what spaceflight does on the human body and mind and genetics. And there actually were really interesting molecular changes. You've probably heard of tieumirs before. They sit on the ends of DNA to protect them and shorten over our lifespan. But lifestyle factors like stress can shorten them faster.
Interestingly, Scott Kelly in space saw a lengthening of his tieumirs, which effectively meant that his cells were biologically younger, but they then shrank rapidly after his return back to Earth. The scientists believe this was an adaptive stress response to microgravity and radiation. While in space, Scott's gene expression also changed. So, while the DNA itself remained stable, different parts turned on and off. Now 91.3% of the changes returned to normal when he came back. But the remaining changes persisted beyond 6 months. Many of which were related to DNA repair, the immune system, and bone formation, suggesting that space flight may actually leave a sort of scar on the body at a cellular level. Despite this finding, his immune
system did seem to function normally. Interestingly, while he was in space, his cognitive test remained high. But after returning back to Earth, he experienced a major brain fog, which was basically a decrease in brain performance on speed and accuracy, which also lasted for about 6 months and was believed to be because of the stress of readapting to Earth's gravity. And finally, other parts of his body changed, too. His corateed artery thickened, and he showed signs of increased inflammation. Like many astronauts, his eyeballs changed shape due to shifts in microgravity, and his microbiome became much less diverse. though that was likely from the strict diet regimen in space. Now, I know these results aren't super relevant to me or
you, but I just thought it was super fascinating that we're even seeing twin studies to understand the effects of interstellar travel. And now for one of the biggest questions. Does your school matter more than your genes? As in, are you born smart? Or does your environment in school actually define your intellectual potential? A recent research paper actually challenges decades of research in this area by changing up how they studied twins raised apart. They basically went through every available study on identical twins that had been raised apart, but that also included individualized data on every participant. So things like their IQ scores, but also their biography so they could understand more about their
schooling and upbringing. They were basically left with 19 studies which translated to 87 twin pairs that were raised separately and had individual biographical data. And this is actually unique because most studies just amalgamate all the twins into one group without these individualized data points. So they look at all these twin studies and say on average the twins separated at birth have an IQ difference of about eight points and a high degree of similarity using a stat called intraclass correlation. And this is a small point difference suggesting that genetics do play the strongest role. But because this study took into account all the individuals, they could then separate them down into further
categories. This group of twins had very similar education. These twins had somewhat dissimilar educational experiences. And this final group had a very dissimilar experience in education. And this calculation drastically changed the results. For those in similar school settings, their IQ difference was just 5.8 points, which makes them almost indistinguishable from twins raised together, who are typically around a six-point difference. For the somewhat dissimilar group, their IQ difference was around 12.1 points, which is closer to the difference between non- twin siblings raised together. And finally, the very dissimilar group had an average IQ difference of 15.1 points. This
difference is nearly the same as two randomly selected unrelated individuals, which is about 17 points. All this to say, their schools were clearly having a massive impact on their IQ scores. As the difference in their schooling increased, so did the difference in their IQs. Now, the biggest caveat with this study is the sample size. Even though they went through every single published study that fit their criteria over the last century, that only left them with 87 pairs of twins. Of course, many more separated twins exist, but the research on them did not include the individualized data or it was not made public. And there is one other interesting caveat found by another
study looking at intelligence. In early childhood, the environment can play a much bigger role in variations of IQ. But as we age, that changes drastically and the genetic component does seem to be much more significant around 70 to 80%. But it highlights how our view of nature versus nurture is constantly evolving. But perhaps it's worth ending on a metaanalysis that looked at the pure question of nature versus nurture. This was a 2015 study that looked at 14.5 million twin pairs over a span of 50 years. So these twins were not necessarily reared apart, but what the meta analysis was trying to find was a literal percentage of importance for
both nature and nurture. Like when we look overall at a vast array of traits, which one comes out the winner? In this case, they were looking at nearly 18,000 traits like height and weight and risk for psychiatric disorders with nearly 3,000 studies, virtually all published twin studies of complex traits between 1958 to 2012. And what they found was that across all traits, the genetic component averages out to, drum roll, 49%. Otherwise known as 50% nature, 50% environment. Of course, each individual trait has widely varying percentages, but when you average them out on a global scale, they're basically perfectly balanced as far as we can tell right now. And this might seem like a
little bit of a yeah, duh, we could have guessed that moment, but this is coming after decades of debate and research and controversy, and only now has really helped move the conversation from which one is more important to really be more about how they actually interact. At the end of the day, these studies show that basically everything is heritable, from height to weight to personality to your desires. But the environment is also responsible for basically half of what makes us who we are on average. Albby found these studies as interesting as I did. I don't know why I was gravitated towards just wanting to know more and finding twins so fascinating in the first place. And knowing that all this
research is out there, it was just a fun time for me to collect together. If you like this content, make sure you subscribe for more. And we will see you ASAP for some more science.
