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Tiny genetic differences add up to big behavioral effects
Many thousands of different genetic variants are responsible for complex behavior.
- Genome-wide association studies (GWAS) allow us to correlate genetic differences with behavioral traits.
- There is no single gene that explains behavior; rather, behavior arises from the complex interaction of many different genes, each of which only plays a small role.
- Society must be cautious as we learn more about behavioral genetics.
Life flourishes with diversity, as diversity gives nature something to choose from, providing flexibility to adapt to change. Variation between humans seems endless, both in appearance and in behavior. Variation between humans is largely due to our flexible nature that allows us to adapt to a wide variety of potential life trajectories, and partly due to set dimensions of variation in our biological make-up carefully molded by the hands of time.
Genome-wide association studies
Four billion years of natural selection crafted the refined machinery we all share — encoded in most of our DNA — as well as carefully selected room for variation — encoded in a minority of DNA differences. If the 3.2 billion nucleotides in our DNA would fit into a 300-page book, the differences between two random people would barely add up to two pages. Many decades of research in twins and family members suggest that considerable portions of differences in human behavior are associated with some of the tiny differences within those two pages.
If the 3.2 billion nucleotides in our DNA would fit into a 300-page book, the differences between two random people would barely add up to two pages.
It is hard to uncover the evolutionary stories behind these differences, but it would probably help to first find out how these genetic differences exactly give rise to the diversity in our behavioral repertoire. Recent advances in genetics research allow us to link specific DNA nucleotides on those two pages to complex behavioral outcomes. Studies that link genetic variation on a molecular level with complex traits are called genome-wide association studies (GWAS). In a GWAS, millions of single DNA nucleotides are tested one by one in order to quantify their relationship with the most complex of human traits, including behavior.
Professor Karin Verweij and I recently published an article in Nature Human Behavior, in which we review what we have learned so far from GWAS on human behavior and what steps we need to take to learn more. Here, I will summarize some highlights from our article and reflect on their societal relevance.
Many genes with tiny effects
In the last decade or so, we have been able to link thousands of genetic variants to human behavioral traits, including personality, education, cognition, sexuality, and mental health. The effects of these genetic variants on behavior are, individually, very weak. Twin and family studies have estimated that, on average, about half of the individual differences in behavioral outcomes are due to genetic differences, which would mean that tens of thousands of genetic variants would be needed to account for these heritability estimates.
The tiny effects of individual genetic variants are hard to estimate, unless unusually large groups are studied. In a typical GWAS, we study millions of DNA variants from hundreds of thousands of individuals. The sum of these small effects can be used to predict people's genetic risk for all kinds of outcomes. The predictive power of DNA is increasing as our studies grow, but we still understand very little about the nature of these predictions.
There are probably no genes that directly influence complex behavioral outcomes. Instead, the many small genetic effects travel through many cascades of mostly unknown biological processes that react to and influence the physical and social environments that people live in.
Before we let DNA prediction reach the clinic or other uses with unpredictable ramifications, such as embryo selection or mate selection, it is important that we first invest in better understanding the nature of the relationship between genetic differences and behavioral outcomes.
Everything is connected
The physical machinery that carries our emergent minds and behaviors consists of many intricate and interconnected systems. Modifying one part will affect multiple other outcomes. This is visible at the level of genes: genetic effects are often shared between different behavioral outcomes in a systematic way. Genes that increase the chances of getting addicted to alcohol tend to increase the risk of feeling lonely. Genes that increase the risk for autism increase the chances of a higher IQ. Genes that increase the risk for anorexia increase the chances of getting a higher education.
These shared genetic effects are widespread among behavioral outcomes. The genetic effects we estimate reflect a patchwork of multiple underlying behavioral outcomes. While many are eager to use these genetic effects to dive into the biology of behavior, we argue that we first need to put more effort into dissecting these genetic effects into their subcomponents.
For educational attainment, for example, we recently split up the part of the genetic effects associated with IQ, which makes up 43 percent of genetic effects on educational attainment, and a "non-IQ" part, making up the remaining 57 percent. We are not sure yet what that remaining 57 percent exactly entails, but we do see that those genes increase the risk for schizophrenia and bipolar disorder. This could be because people with a higher genetic risk for schizophrenia or bipolar disorder tend to be more creative and more open to new experiences.
These shared genetic effects teach us a lot about the genetic architecture of human behavior and also make us realize that it is difficult to select for one trait without also influencing many others. This is a strong argument against using DNA prediction to influence your offspring's DNA through embryo selection, a service that, unfortunately, some companies have already started to offer.
Behavioral genetics is controversial
The highest portion of shared genetic effects was observed between educational attainment and income. These associations have been reported in separate publications, and the genetic effect on each is roughly the same. Both publications received much attention in the media and on social media. While for educational attainment, the reactions were mostly positive, the publication on genetic effects on income was met mostly with criticism.
These opposite reactions to the same genetic signal might have to do with income being more closely associated in people's minds with social inequalities. Trying to explain social inequalities in terms of something that people are born with may instill the fear that science is being misused to justify the position of marginalized groups. Instead, these molecular genetic effects are helping to elucidate an inherent unfairness in the way we organize our societies.
A closer look at these genetic effects shows that they contain substantial amounts of environmental influences. Our initial studies had trouble separating the two because they are highly correlated. When your genes predispose you to a higher education, that means that your parents also carry those genes and are thus more likely to also have a higher education, giving them better resources (money) to nurture you with a better environment. If you are born with genes that make it easier for you to learn, it will also increase the chances that you will move to a richer neighborhood with healthier living circumstances. These "double advantages" and "double disadvantages" make us mistake the impact of systematic social disadvantages for genetic effects, inflating heritability estimates.
These gene-environment correlations were recently detected studying DNA from people that were exclusively of white European origin. Systematic differences in environmental influences are likely much worse between different ethnic groups, casting more doubts on white supremacists' claims who love to use these inflated heritability estimates to support their genetic explanations for socio-economic group differences.
After two decades of reading out human genomes, we are still only scratching their surface. We are just starting to dissect only a fraction of the total heritability that we are currently able to capture with molecular genetic data. Large parts of humanity are still underrepresented in our measurements, which makes it difficult to make more general claims. We outline in more detail in our Nature Human Behavior paper which steps we need to take in our methods and data collection strategies to better understand the differences in our DNA.
Abdel Abdellaoui & Karin J.H. Verweij (2021). Dissecting polygenic signals from genome-wide association studies on human behavior. Nature Human Behavior. https://doi.org/10.1038/s41562-021-01110-y
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So much for rest in peace.
- Australian scientists found that bodies kept moving for 17 months after being pronounced dead.
- Researchers used photography capture technology in 30-minute intervals every day to capture the movement.
- This study could help better identify time of death.
We're learning more new things about death everyday. Much has been said and theorized about the great divide between life and the Great Beyond. While everyone and every culture has their own philosophies and unique ideas on the subject, we're beginning to learn a lot of new scientific facts about the deceased corporeal form.
An Australian scientist has found that human bodies move for more than a year after being pronounced dead. These findings could have implications for fields as diverse as pathology to criminology.
Dead bodies keep moving
Researcher Alyson Wilson studied and photographed the movements of corpses over a 17 month timeframe. She recently told Agence France Presse about the shocking details of her discovery.
Reportedly, she and her team focused a camera for 17 months at the Australian Facility for Taphonomic Experimental Research (AFTER), taking images of a corpse every 30 minutes during the day. For the entire 17 month duration, the corpse continually moved.
"What we found was that the arms were significantly moving, so that arms that started off down beside the body ended up out to the side of the body," Wilson said.
The researchers mostly expected some kind of movement during the very early stages of decomposition, but Wilson further explained that their continual movement completely surprised the team:
"We think the movements relate to the process of decomposition, as the body mummifies and the ligaments dry out."
During one of the studies, arms that had been next to the body eventually ended up akimbo on their side.
The team's subject was one of the bodies stored at the "body farm," which sits on the outskirts of Sydney. (Wilson took a flight every month to check in on the cadaver.)Her findings were recently published in the journal, Forensic Science International: Synergy.
Implications of the study
The researchers believe that understanding these after death movements and decomposition rate could help better estimate the time of death. Police for example could benefit from this as they'd be able to give a timeframe to missing persons and link that up with an unidentified corpse. According to the team:
"Understanding decomposition rates for a human donor in the Australian environment is important for police, forensic anthropologists, and pathologists for the estimation of PMI to assist with the identification of unknown victims, as well as the investigation of criminal activity."
While scientists haven't found any evidence of necromancy. . . the discovery remains a curious new understanding about what happens with the body after we die.
Metal-like materials have been discovered in a very strange place.
- Bristle worms are odd-looking, spiky, segmented worms with super-strong jaws.
- Researchers have discovered that the jaws contain metal.
- It appears that biological processes could one day be used to manufacture metals.
The bristle worm, also known as polychaetes, has been around for an estimated 500 million years. Scientists believe that the super-resilient species has survived five mass extinctions, and there are some 10,000 species of them.
Be glad if you haven't encountered a bristle worm. Getting stung by one is an extremely itchy affair, as people who own saltwater aquariums can tell you after they've accidentally touched a bristle worm that hitchhiked into a tank aboard a live rock.
Bristle worms are typically one to six inches long when found in a tank, but capable of growing up to 24 inches long. All polychaetes have a segmented body, with each segment possessing a pair of legs, or parapodia, with tiny bristles. ("Polychaeate" is Greek for "much hair.") The parapodia and its bristles can shoot outward to snag prey, which is then transferred to a bristle worm's eversible mouth.
The jaws of one bristle worm — Platynereis dumerilii — are super-tough, virtually unbreakable. It turns out, according to a new study from researchers at the Technical University of Vienna, this strength is due to metal atoms.
Metals, not minerals
Fireworm, a type of bristle wormCredit: prilfish / Flickr
This is pretty unusual. The study's senior author Christian Hellmich explains: "The materials that vertebrates are made of are well researched. Bones, for example, are very hierarchically structured: There are organic and mineral parts, tiny structures are combined to form larger structures, which in turn form even larger structures."
The bristle worm jaw, by contrast, replaces the minerals from which other creatures' bones are built with atoms of magnesium and zinc arranged in a super-strong structure. It's this structure that is key. "On its own," he says, "the fact that there are metal atoms in the bristle worm jaw does not explain its excellent material properties."
Just deformable enough
Credit: by-studio / Adobe Stock
What makes conventional metal so strong is not just its atoms but the interactions between the atoms and the ways in which they slide against each other. The sliding allows for a small amount of elastoplastic deformation when pressure is applied, endowing metals with just enough malleability not to break, crack, or shatter.
Co-author Florian Raible of Max Perutz Labs surmises, "The construction principle that has made bristle worm jaws so successful apparently originated about 500 million years ago."
Raible explains, "The metal ions are incorporated directly into the protein chains and then ensure that different protein chains are held together." This leads to the creation of three-dimensional shapes the bristle worm can pack together into a structure that's just malleable enough to withstand a significant amount of force.
"It is precisely this combination," says the study's lead author Luis Zelaya-Lainez, "of high strength and deformability that is normally characteristic of metals.
So the bristle worm jaw is both metal-like and yet not. As Zelaya-Lainez puts it, "Here we are dealing with a completely different material, but interestingly, the metal atoms still provide strength and deformability there, just like in a piece of metal."
Observing the creation of a metal-like material from biological processes is a bit of a surprise and may suggest new approaches to materials development. "Biology could serve as inspiration here," says Hellmich, "for completely new kinds of materials. Perhaps it is even possible to produce high-performance materials in a biological way — much more efficiently and environmentally friendly than we manage today."
Dealing with rudeness can nudge you toward cognitive errors.
- Anchoring is a common bias that makes people fixate on one piece of data.
- A study showed that those who experienced rudeness were more likely to anchor themselves to bad data.
- In some simulations with medical students, this effect led to higher mortality rates.
Cognitive biases are funny little things. Everyone has them, nobody likes to admit it, and they can range from minor to severe depending on the situation. Biases can be influenced by factors as subtle as our mood or various personality traits.
A new study soon to be published in the Journal of Applied Psychology suggests that experiencing rudeness can be added to the list. More disturbingly, the study's findings suggest that it is a strong enough effect to impact how medical professionals diagnose patients.
Life hack: don't be rude to your doctor
The team of researchers behind the project tested to see if participants could be influenced by the common anchoring bias, defined by the researchers as "the tendency to rely too heavily or fixate on one piece of information when making judgments and decisions." Most people have experienced it. One of its more common forms involves being given a particular value, say in negotiations on price, which then becomes the center of reasoning even when reason would suggest that number should be ignored.
It can also pop up in medicine. As co-author Dr. Trevor Foulk explains, "If you go into the doctor and say 'I think I'm having a heart attack,' that can become an anchor and the doctor may get fixated on that diagnosis, even if you're just having indigestion. If doctors don't move off anchors enough, they'll start treating the wrong thing."
Lots of things can make somebody more or less likely to anchor themselves to an idea. The authors of the study, who have several papers on the effects of rudeness, decided to see if that could also cause people to stumble into cognitive errors. Past research suggested that exposure to rudeness can limit people's perspective — perhaps anchoring them.
In the first version of the study, medical students were given a hypothetical patient to treat and access to information on their condition alongside an (incorrect) suggestion on what the condition was. This served as the anchor. In some versions of the tests, the students overheard two doctors arguing rudely before diagnosing the patient. Later variations switched the diagnosis test for business negotiations or workplace tasks while maintaining the exposure to rudeness.
Across all iterations of the test, those exposed to rudeness were more likely to anchor themselves to the initial, incorrect suggestion despite the availability of evidence against it. This was less significant for study participants who scored higher on a test of how wide of a perspective they tended to have. The disposition of these participants, who answered in the affirmative to questions like, "Before criticizing somebody, I try to imagine how I would feel if I were in his/her place," was able to effectively negate the narrowing effects of rudeness.
What this means for you and your healthcare
The effects of anchoring when a medical diagnosis is on the line can be substantial. Dr. Foulk explains that, in some simulations, exposure to rudeness can raise the mortality rate as doctors fixate on the wrong problems.
The authors of the study suggest that managers take a keener interest in ensuring civility in workplaces and giving employees the tools they need to avoid judgment errors after dealing with rudeness. These steps could help prevent anchoring.
Also, you might consider being nicer to people.