You are an educated reader, so I know that you know that vaccines do not cause autism. However, you probably have also read headlines such as the recent U.S. Health and Human Services release, “Autism Epidemic Runs Rampant.” Is there an epidemic-level increase in autism rates? Are vaccines involved in any way? Autism spectrum disorder (ASD) diagnoses have multiplied. Successive editions of my introductory psychology texts have offered updated Centers for Disease Control and Prevention estimates of U.S. childhood autism rates: My ninth edition, published in 2009, reported that 1 in 150 children were diagnosed. Tenth edition (2012): 1 in 110 Eleventh edition (2014): 1 in 68 Twelfth edition (2020): 1 in 59 Fourteenth edition (2023): 1 in 54 Briefer edition (2024): 1 in 38 Briefest edition (2025): 1 in 31 There are at least two possible contributors to a genuine autism increase. Premature babies more often get diagnosed with autism, and with medical advances today’s preemies more often survive to experience childhood. Also, older parents more often give birth to children with autism, so the increasing age of birthing parents may contribute. But other possibilities seemingly explain most of the increased autism reporting: Relabeling of children’s disorders. Increased ASD diagnoses have been partly offset by a decrease in children diagnosed with “cognitive disability” or “learning disability.” Better detection. The quintupled rate of autism diagnoses since 2009 also results from increased awareness and early autism detection—rather like breast cancer diagnoses increasing during the 1980s thanks to mammography adoption. Expanded labeling. Broadened criteria for ASD diagnosis may have led to some “concept creep.” With more clinicians trained in early detection, children are being diagnosed today who might earlier have just been considered a bit different. If growing up today, Bill Gates believes he would have been diagnosed with ASD. He reports that, as a child, he was “obsessed with certain projects, missed social cues and could be rude or inappropriate without seeming to notice his effect on others.” As an interviewer noted, “He still rocks back and forth like a metronome as he talks [and] thinks his superpower is his neurodiversity and ability to hyperfocus—he can remember all the number plates of his first employees.” So, to answer my first question, there does appear to be some actual autism increase, though the bigger contributor is likely more liberal diagnosing of children. Now to my second question: What causes autism, and might vaccines be even a small contributor? Vaccines do not cause autism. However, the subtle power of repetition (“vaccines cause autism”) seems to have caused many people to wonder if increased childhood vaccinations partially contribute to an “autism epidemic.” If you are unsure, you have much company, as evident from a 2025 KFF U.S survey: Children receive a measles/mumps/rubella (MMR) vaccination in early childhood, about the time ASD symptoms first get noticed. So, it’s understandable that some parents presumed the vaccination caused the ensuing ASD, an idea that spread after a 1998 British study claimed to have found a vaccine–autism connection. But that anti-vax-inspiring study—“the most damaging medical hoax of the last 100 years”—turned out to be fraudulent. The publication was retracted and its medical author disbarred. Others have worried that thimerosal, a mercury vaccine preservative, might cause autism. But experts discount that possibility, noting also that childhood vaccines since 2001 have been thimerosal-free. Even so, vaccine doubts and fears persist, contributing to this year’s measles outbreak. Yet the evidence could not be clearer. Studies of a gazillion children, including one following more than a million, reveal identical autism rates in those vaccinated and unvaccinated. A slight exception was one study that followed nearly 700,000 Danish children: Those receiving the MMR vaccine were slightly less likely to later be among the 6517 ASD-diagnosed children. Moreover, among children diagnosed with autism after vaccinations, family home movies have revealed less eye contact and other early autism symptoms appearing before vaccination. Although vaccines clearly do not cause autism, other biological factors do. As we document in Psychology, Fourteenth Edition, the prenatal environment can matter, especially when altered by maternal infection, toxins, psychiatric drug use, or stress. But multiple genes matter more. One five-nation study of 2 million people found the heritability of ASD was near 80 percent. If one identical twin is diagnosed with ASD, the chances are about 9 in 10 that the co-twin will be as well, although such twins often differ in symptom severity. So, is there an autism epidemic? There has definitely been a multiplication of autism spectrum diagnoses, to which in utero biology contributes, though the increase appears to be due more to expansive diagnoses. Regardless, vaccines do not contribute. And such neurodiversity can have an upside. As the scientist Temple Grandin reportedly explained on behalf of those sharing her autism diagnosis, “The most interesting people you’ll find are ones that don’t fit into your average cardboard box.” Bill Gates would agree: “If they ever invent a pill where they could say, ‘OK, your social skills will be normal, but your ability to concentrate would also be normal,’ I wouldn’t take the pill.” [June 23, 2025 update: Psychiatrist Allen Frances, who led the task force that created the DSM's expanded definition of ASD, explains here how the changing definition--blurring "the boundary between autism and social awkwardness"--explains the multiplying diagnoses (it's not vaccine related).]  David Myers, a Hope College social psychologist, authors psychology textbooks and trade books, including his recent essay collection, How Do We Know Ourselves? Curiosities and Marvels of the Human Mind. ... View more

As members of one species, we humans share both a common biology (cut us and we bleed) and common behaviors (we similarly sense the world around us, use language, and produce and protect children). Our human genes help explain our kinship—our shared human nature. And they contribute to our individual diversity: Some people, compared with others, are taller, smarter, skinnier, healthier, more temperamental, shyer, more athletic . . . the list goes on and on. Across generations, your ancestors shuffled their gene decks, leading to the hand that—with no credit or blame due you—you were dealt. If you are reading this, it’s likely that genetic luck contributed to your having above average intelligence. Others, dealt a different hand and a different life, would struggle to understand these words. Andrew Brookes/Image Source/Getty Images Individual variation is big. Individuals vary much, much more within groups (say, comparing Danes with Danes or Kenyans with Kenyans) than between groups (as when comparing Danes and Kenyans). Yet there are also group differences. Given this reality (some groups struggle more in school), does behavior genetic science validate ethnocentric beliefs and counter efforts to create a just and equal society? In The Genetic Lottery: Why DNA Matters for Social Equality, University of Texas behavior geneticist Kathryn Paige Harden answers an emphatic no. She documents the power of genes, but also makes the case for an egalitarian culture in which everyone thrives. Among her conclusions are these: We all are family. Going back far enough in time to somewhere between 5000 and 2000 B.C., we reach a remarkable point where “everyone alive then, if they left any descendants at all, was a common ancestor of everyone alive now.” We are all kin beneath the skin. We’re each highly improbable people. “Each pair of parents could produce over 70 trillion genetically unique offspring.” If you like yourself, count yourself fortunate. Most genes have tiny effects. Ignore talk of a single “gay gene” or “smart gene.” The human traits we care about, including our personality, mental health, intelligence, longevity, and sexual orientation “are influenced by many (very, very, very many) genetic variants, each of which contributes only a tiny drop of water to the swimming pool of genes that make a difference.” Individual genes’ tiny effects may nevertheless add up to big effects. Today’s Genome Wide Association Studies (GWAS) measure millions of genome elements and correlate each with an observed trait (phenotype). The resulting miniscule correlations from thousands of genetic variants often “add up to meaningful differences between people.” Among the White American high school students in one large study, only 11 percent of those who had the lowest GWAS polygenic index score predicting school success later graduated from college, as did 55 percent of those who had the highest score. “That kind of gap—a fivefold increase in the rate of college graduation—is anything but trivial.” Twin studies confirm big genetic effects. “After fifty years and more than 1 million twins, the overwhelming conclusion is that when people inherit different genes, their lives turn out differently.” Parent-child correlations come with no causal arrows. If the children of well-spoken parents who read to them have larger vocabularies, the correlation could be environmental, or genetic, or some interactive combination of the two. Beware the ecological fallacy (jumping from one data level to another). Genetic contributions to individual differences within groups (such as among White American high school students) provide zero evidence of genetic differences between groups. Genetic science does not explain social inequalities. Harden quotes sociologist Christopher Jencks’ illustration of a genetically influenced trait eliciting an environmentally caused outcome: “If, for example, a nation refuses to send children with red hair to school, the genes that cause red hair can be said to lower reading scores.”  Harden also quotes social scientist Ben Domingue: “Genetics are a useful mechanism for understanding why people from relatively similar backgrounds end up different. . . . But genetics is a poor tool for understanding why people from manifestly different starting points don’t end up the same.” Many progressives affirm some genetic influences on individual traits. For example, unlike some conservatives who may see sexual orientation as a moral choice, progressives more often understand sexual orientation as a genetically influenced natural disposition. Differences ≠ deficits. “The problem to be fixed is society’s recalcitrant unwillingness to arrange itself in ways that allow everyone, regardless of which genetic variants they inherit, to participate fully in the social and economic life of [their] country.” An example: For neurodiverse individuals, the question is how to design environments that match their skills. Behavior genetics should be anti-eugenic. Advocates of eugenics have implied that traits are fixed due to genetic influences, and may therefore deny the value of social interventions. Alternatively, some genome-blind advocates shun behavior genetics science that could inform both our self-understanding and public policy. Harden advocates a third option, an anti-eugenic perspective that, she says, would reduce the waste of time and resources on well-meaning but ineffective programs. For example, by controlling for genetic differences with a GWAS measure, researchers can more accurately confirm the actual benefits of an environmental intervention such as an educational initiative or income support. Anti-eugenics also, she contends, uses genetic information to improve lives, not classify people, uses genetic information to promote equity, not exclusion, doesn’t mistake being lucky in a Western capitalist society for being “good” or deserving, and considers what policies people would favor if they didn’t know who they would be. Harden’s bottom line: Acknowledging the realities of human diversity, and discerning the powers and limits of various environmental interventions, can enhance our quest for a just and fair society. (For David Myers’ other essays on psychological science and everyday life, visit TalkPsych.com. Follow him on Twitter: @davidgmyers.) ... View more

Judith Rich Harris’ December 29th death took my mind to her remarkable life and legacy. Among all the people I’ve never met, she was the person I came to know best. Across 243 emails she shared her draft writings, her critical assessment of others’ thinking (including my own), and the progress of her illness. Our conversation began after the publication of her cogent Psychological Review paper, which changed my thinking and led me to send a note of appreciation. The paper’s gist was delivered by its first two sentences: “Do parents have any important long-term effects on the development of their child’s personality? This article examines the evidence and concludes that the answer is no.” Her argument: Behavior genetics studies (of twins and adoptees) show that genes predispose our individual traits, and that siblings’ “shared environment” has a shockingly small influence. Peers also matter—they transmit culture. Show her some children who hear English spoken with one accent at home, and another accent at school and in the neighborhood, and—virtually without exception—she will show you children who talk like their peers. Judy Harris was a one-time Harvard psychology graduate student who was dismissed from its doctoral program because, as George Miller explained to her, she lacked “originality and independence.” But she persisted. In her mid-fifties, without any academic affiliation and coping with debilitating autoimmune disorders, she had the chutzpah to submit her evidence-based ideas to Psychological Review, then as now psychology’s premier theoretical journal. To his credit, the editor, Daniel Wegner, welcomed this contribution from this little-known independent scholar. Moreover, when her great encourager Steven Pinker and I each nominated her paper for the annual award for “outstanding paper on general psychology,” the judges selected her as co-recipient of the—I am not making this up—George A. Miller Award. (To his credit, Miller later termed the irony “delicious.”) The encouraging lesson (in Harris’ words😞 “‘Shut in’ does not necessarily mean ‘shut out.’” Truth will out. Although biases are real, excellence can get recognized. So, wherever you are, whatever your big idea or passion, keep on. Her fame expanded with the publication of her 1998 book The Nurture Assumption, which was profiled by Malcolm Gladwell in a New Yorker feature article, made into a Newsweek cover story, and named as a Pulitzer Prize finalist. Her argument was controversial, and a reminder that important lessons are often taught by those who fearlessly push an argument to its limit. (Surely child-rearing does have some direct influence on children’s values, religiosity, and politics—and not just via the peer culture to which parents expose children. And surely the loving versus abusive extremes of parenting matter.) Harris was kind and generous (she supportively critiqued my writing, even as I did hers) but also had the self-confidence to take on all critics and to offer challenges to other widely accepted ideas. One was the “new science” of birth order, which, as she wrote me, was “neither new nor science.” An August 24, 1997, email gives the flavor of her wit and writing: Birth order keeps coming back. In their 1996 book on birth order and political behavior, Albert Somit, Alan Arwine, and Steven A. Peterson spoke of the “inherent non-rational nature of deeply held beliefs” and mused that “permanently slaying a vampire”—the belief in birth order effect—may require “that a stake of gold be driven through his/her heart at high noon” (p. vi).             Why is it so difficult to slay this vampire? Why, in spite of all the telling assaults that have been made on it, does it keep coming back? The answer is that the belief in birth order effects fits so well into the basic assumptions of our profession and our culture. Psychologists and nonpsychologists alike take it for granted that a child’s personality, to the degree that it is shaped by the environment, receives that shaping primarily at home. And since we know (from our own memories and introspections) that a child’s experiences at home are very much affected by his or her position in the family—oldest, youngest, or in the middle—we expect birth order to leave permanent marks on the personality.             The belief in birth order effects never dies; it just rests in its coffin until someone lifts the lid again. Alas, the disease that shut her in has, as she anticipated, claimed her. In her last email sent my way on September 6, 2018, she reported that I’m not doing so well. This is the normal course of the disorder I have—pulmonary arterial hypertension. It is incurable and eventually progresses to heart failure and death. I’m in the heart failure stage now. It’s progressing very slowly, but makes remaining alive not much fun.              Because I can’t actually DO anything anymore, it’s a treat to get your mail. I can’t do any more than I’ve already done, but maybe what I’ve already done is enough. Who would have thought that 20 years after its publication, people would still be talking about The Nurture Assumption! Or that The New York Times would replay its message at length, in your well-deserved obituary, Judy. (For David Myers’ other essays on psychological science and everyday life visit www.TalkPsych.com.) ... View more