Can Cognitive Training Make You Smarter?

Monday, April 21st, 2014

Dan Hurley (Smarter: The New Science of Building Brain Power) discusses cognitive training:

What kind of effect does cognitive training have on the brain?

There is no question that training causes structural and functional improvement in the brain, as seen on MRI. Most of the changes are seen in the frontal areas of the brain, where high-level thinking occurs. Mindfulness meditation, for instance, has been shown to produce increased white-matter connections between the anterior cingulate cortex, an important region for complex decision-making, and the rest of the brain.

What cognitive functions did you find are most trainable?

Working memory is the ability to juggle multiple items of attention, to manipulate and analyze information. If you try to multiple 26 by 37 in your head, the reason it’s so hard is because of the demands it puts on your working memory. Tons of studies, including the latest one by Randy Engle, show that by training on certain kinds of working-memory tasks, you can improve your working memory overall. This is profoundly important for your ability to multi-task and think through complicated problems.

What interventions are the most effective in improving cognitive ability?

Working-memory training has proved really useful, although exactly which kinds of working-memory tasks are most useful remains unclear. Susanne Jaeggi has focused on the N-back task, which anyone can check out online at www.soakyourbrain.com.  Others prefer various other kinds of working-memory tasks. But plenty of research also shows that physical exercise, learning a musical instrument, and mindfulness meditation can all bring significant benefits. One of the coolest parts of my training was learning to play the Renaissance lute.

Teenagers everywhere want to know: are there any cognitive benefits of first-person shooter games?

Absolutely. These games are so good at improving reaction times that they are used by the U.S. military to train pilots and operators of drones. These games can also improve the “useful field of view,” your ability to see and respond to stimuli at the periphery of your vision, which is incredibly important when driving a vehicle. Other computerized games have been shown to improve older people’s ability to distinguish very fine differences in shades of gray. Strangely, this ability has been shown to be one of the single most important markers of longevity. So if you get better at it, will you actually live longer? That’s not yet clear. But improving your ability to see and respond to your environment can be potentially lifesaving.

How important is exercise?

Research has proved beyond doubt that the brain is actually connected to the heart and lungs via something called the “neck.” Physical exercise is perhaps the best-proved method for improving cognitive function in older people. It’s also critical for children and middle-aged sloths. Some researchers believe that cardiovascular exercise is best, while others insist that strength training is more important.

What about vitamins? Which one should take the most of if I want to think more quickly? Or should I just continue to drink lots and lots of caffeine?

I know that many people believe in the benefits of vitamins and dietary supplements. But there are no good studies showing that any of them really help cognitive function. Large studies of fish oil given to pregnant women have even suggested that there might be some risks to the intellectual abilities of their children. Caffeine, on the other hand, has been repeatedly shown to enhance not just attention, but motivation and even, most recently, memory. And if you can believe it, nicotine also helps. Cigarettes and other forms of tobacco are of course extremely dangerous and greatly increase the risk of cancer, heart disease, and much more. But studies in both humans and animals confirm that nicotine, given through a patch or gum, can be a great cognitive enhancer. I actually started using a 7 mg nicotine patch and found it useful, without any noticeable addictiveness.

Can mindfulness meditation make you smarter? What cognitive functions are most affected by mindfulness meditation?

A series of studies by Michael Posner and Yi-Yuan Tang have shown that mindfulness meditation can enhance all kinds of cognitive abilities. Mind-wandering is not helpful when you’re trying to write an article or take a test. On the other hand, some recent studies have suggested that allowing your mind to wander can also be helpful when you need a breakthrough. Some of the greatest scientific insights have occurred when scientists were spacing out.

How transferable are improvements in specific cognitive functions to intelligence more generally?

It’s easy for psychologists to give you a series of tests, have you practice some exercises, and then run follow-up tests to see if you improve better than people who didn’t do those exercises. But figuring out what the real-world benefits are to those improvements is much, much harder. A recent study of older adults given just ten hours of training found that even ten years later, they still enjoyed significant benefits in daily functioning. A hundred years of studies have proved that IQ tests and other tests of cognitive function are very, very predictive of real-world abilities. They’re not perfect—no test is—but on average, just like blood-pressure tests, they’re pretty good at predicting how you’ll do in the future. Many large corporations, as well as the U.S. military, give these tests not because they love tests, but because they really help pick out people who can be successful from those who just lack the ability to learn and function.

The Science of Successful Learning

Monday, April 21st, 2014

Peter C. Brown, Henry L. Roediger III, and Mark A. McDaniel summarize the science of successful learning — which, in modern Internet fashion, garners the headline, Ditch the 10,000 hour rule! Why Malcolm Gladwell’s famous advice falls short.

Malcolm Gladwell’s 10,000-hour rule is often mischaracterized. First, it’s not Malcolm Gladwell’s rule; he simply popularized the work of Ericsson et al. Second, the rule is not that 10,000 hours of practice will guaranty mastery of a skill; it’s that those who had mastered a skill had spent an average of 10,000 hours in deliberate practice, often on their own, while second-tier experts had spent their time playing their instrument (or whatever) in not-so-deliberate practice.

So, that 10,000-hour cut-off isn’t hard and fast.

Anyway, the science of successful learning suggests that many popular training tactics improve performance in the very short term while reducing the amount of learning over the long term. So, if you practice the exact same thing, over and over, in dedicated training sessions, you will see clear improvement from the start of each session to the end of each session — at least until you get tired and bored — but you’ll improve less than if you if interleaved multiple skills into each session, spaced out your training, varied each challenge a bit, and so on.

Robin Hanson doesn’t see modern teaching methods as a mere misunderstanding of the science of successful learning:

If school’s purpose were to develop skills, we’d teach differently.

[...]

So, a good test of a theory of school is: how long do you predict it will take teachers to learn this lesson? The article above talks about how many coaches have learned this lesson, plausibly because they really do want to win games, and face strong competitive pressures.

If you think the main function of schools is something other than learning, you might think it could take a very long time before schools adopt these practices. If you think the main function of schools is learning, but that public schools face much weaker pressures to be efficient that private schools, you might predict that private schools will adopt this much faster. If you think public schools are effective at adopting better approaches, you might predict that they adopt these quickly.

Activities and Programs that Improve Children’s Executive Functions

Monday, April 21st, 2014

Executive functions — such as reasoning, working memory, and self-control — can be improved through various acitivities, Adele Diamond has found:

The best evidence exists for computer-based training, traditional martial arts, and two school curricula. Weaker evidence, though strong enough to pass peer review, exists for aerobics, yoga, mindfulness, and other school curricula. Here I address what can be learned from the research thus far, including that EFs need to be progressively challenged as children improve and that repeated practice is key. Children devote time and effort to activities they love; therefore, EF interventions might use children’s motivation to advantage. Focusing narrowly on EFs or aerobic activity alone appears not to be as efficacious in improving EFs as also addressing children’s emotional, social, and character development (as do martial arts, yoga, and curricula shown to improve EFs). Children with poorer EFs benefit more from training; hence, training might provide them an opportunity to “catch up” with their peers and not be left behind. Remaining questions include how long benefits of EF training last and who benefits most from which activities.

Manual for Civilization

Thursday, April 17th, 2014

The Long Now Foundation is taking recommendations for their library-sized Manual for Civilization. Kevin Kelly originally called for a Library of Utility:

It would be a very selective library. It would not contain the world’s great literature, or varied accounts of history, or deep knowledge of ethnic wonders, or speculations about the future. It has no records of past news, no children’s books, no tomes on philosophy. It contains only seeds. Seeds of utilitarian know-how. How to recreate the infrastructure and technology of civilization so far.

The idea evolved to include these categories:

  • Cultural Canon (Great Books, Shakespeare, Plato, etc.)
  • Mechanics of Civilization (Technical knowledge, how to build and understand things)
  • Rigorous Science Fiction (Science fiction that tells a useful story about a potential future)
  • Long-term Thinking, Futurism, and relevant history (Books on how to think about the future that may include surveys of the past)

Brian Eno’s recommendations were the first to be shared:

I’m inclined to see Steward Brand’s recommendations as definitive.

Orbital Mechanics

Wednesday, April 16th, 2014

The latest xkcd comic, on orbital mechanics, reminds us how powerful simulations are as learning tools:

xkcd Orbital Mechanics

Good Drug, Bad Delivery System

Tuesday, April 15th, 2014

Who smokes? And why?

Warner: If you look at the population that is at the poverty line or above it, about 18% of them are smokers. If you look at the population below the poverty line, it’s about 29%. If you look at college graduates, 7.5% of them smoke today. If you look at people with only 9 to 11 years of high school education it’s about 36% percent. If we go back to the time of the Surgeon General’s report…

Dubner: That, remember, was 1964.

Warner: …those numbers were very close to each other. So that’s a huge issue, is a socio-economic disparity. And then there is one we that have finally started to recognize and talk about in the field of tobacco control and it is very important — perhaps as many as 40 to 50 percent of all smokers have a concurrent mental health disability or morbidity and/or other substance-abuse problem. The cigarette industry has always liked to talk about smoking as being a rational choice of well-informed adults and yet we have this strong correlation between smoking and mental illness.

Dubner: So this opens up a whole other way to look at smoking – that it is, to some degree, self-medication, with side effects of course. Paul Newhouse is an m.d. who runs the Center for Cognitive Medicine at Vanderbilt. For 30 years, he’s been studying the effects of nicotine on the brain:

Newhouse: We jokingly say in our lab: You know, good drug, bad delivery system.

Dubner: Newhouse tells us that nicotine itself has a number of potentially positive characteristics.

Newhouse: It appears to activate a class of what we call receptors important for regulating a whole variety of brain functions. And so we think that nicotinic receptors are important for things like attention, for behavioral strategies, for what we call executive functioning, which is the ability to make decisions and evaluate information, we think it’s important for memory, and so that has kind of led us to thinking about what particular disorders might be helped by stimulating nicotinic receptors either with nicotine or with something else.

Dubner: So Newhouse and others in his field are exploring if nicotine therapy might be used to treat schizophrenia, Parkinson’s disease, or other maladies.

Newhouse: Things like memory loss disorders, Alzheimer’s disease, pre-Alzheimer’s disease, which is called mild cognitive impairment, we’ve looked at ADHD, attention deficit hyperactivity disorder. Other investigators have looked at things from Tourette’s Syndrome to anxiety disorders to depression. I think the full potential of nicotine and nicotinic drugs is really not even fully known yet.

Dubner: Newhouse does believe, however, that nicotine has medicinal effects, and that is why some smokers smoke.

Newhouse: If you look at heavy smokers you will find that many of them have mood disorders or anxiety disorders as well. The rates of psychological problems among heavy smokers these days are very high. And we think that one of the reasons they smoke is because it produces benefits to them. Maybe it improves their mood, maybe it stabilizes their anxiety, maybe it helps them pay attention or inhibit impulsiveness, etc.

Infant IQ Tests Predict Scores in School

Monday, April 14th, 2014

Twenty-five years ago, Gina Kolata of the New York Times reported on infant IQ tests that predicted later school performance:

The tests, which attempt to measure what babies remember, are based on the assumption that they will be more interested in stimuli they have not previously encountered. One test involves showing infants photographs or pictures and measuring how long they look at them. In theory, babies will look at a new stimulus for a longer time than one they remember having seen before. Babies that are likely to be below average in intelligence will remember fewer of the stimuli they have seen before.

Working independently, Dr. Bornstein and Susan Rose of Albert Einstein College of Medicine in New York have found that a baby’s performance at age 4 months and 6 months on tests of visual memory correlate with I.Q. at 4 and 6 years of age. They used tests that they developed themselves but that are similar to those developed by Dr. Fagan. The predictions are independent of the parents’ education and income group, which also are correlated with I.Q.

The original article is full of fears that such tests might give already-advantaged children even more advantages.

Kenneth Change, also of the Times, revisits the original article:

For the most part, the validity of the Fagan test holds up. Indeed, Dr. Fagan (who died last August) and Dr. Holland revisited infants they had tested in the 1980s, and found that the Fagan scores were predictive of the I.Q. and academic achievement two decades later when these babies turned 21.

“It’s really good science,” said Scott Barry Kaufman, scientific director of the Imagination Institute at the University of Pennsylvania and the author of “Ungifted: Intelligence Redefined.”

But Dr. Fagan’s hope for widespread screening of infants has not come to pass. “There are some centers that have it,” Dr. Holland said. “It never came to be the kind of thing where it’s widely available.”

The trend is perhaps in the other direction, away from dividing young children by I.Q. and its surrogates out of concerns that the labels become self-fulfilling prophecies. Private schools in New York City, for example, have agreed to abandon intelligence tests for 4- and 5-year-old applicants.

This stands out:

For the last decade of his life, Dr. Fagan was unexpectedly drawn into the “genes versus environment” debate over intelligence after he found that babies from widely different cultural backgrounds performed equally well on his test. That, he argued, undercut the argument for a biological basis for the stark “achievement gap” between white and black children, or rich and poor.

Culture, Resources, or Genetics

Sunday, April 13th, 2014

Gregory Clark discusses social mobility — or the lack of it — and whether it comes down to culture, resources, or genetics:

DE: So social mobility does take place but over many generations. What are the mechanisms by which people revert to the mean?

GC: For me, as a social scientist, this is the most interesting part of the story. The question that really comes up is: is this a cultural phenomena? Is it a familial culture that is being passed on? Is it resources? Or is the basic genetics of inheritance? And if it’s cultural or resources, what it says is that societies are dramatically failing to achieve appropriate rates of social mobility; that it’s a number one problem for all societies; that President Obama is right to say that this is the problem his administration will tackle. If it’s just a basic issue of genetics and of assortative mating and then the transmission of certain types of abilities or competencies, then actually two things: one is we don’t have a problem. And the second thing is we shouldn’t devote enormous resources to trying to deal with it.

DE: So let me press you on that. So, one interpretation is that all that’s happening is that intelligent people are passing their genes on to intelligent people and so remaining in the elite. Another is that there are barriers to a meritocratic society. Which is it?

GC: My own personal bet is that genetics plays a much greater role in this than people have been willing to consider. One test would be, in cultural explanations, your grandparents; your cousins; your other relatives should all have some influence on your outcomes. If you’re from the Jewish community, for example, then being part of that larger community network should have significant influence on your outcomes. In a genetic interpretation, if we truly knew the status of your parents – the underlying status – that would be the only predictor of your outcomes. Your grandparents, all the rest of the stuff would not matter. And also, things like resource shocks should be relatively unimportant. And interestingly, again using Oxford and Cambridge data, we can actually test. do your parents only matter or does your more extended lineage matter to predicting future success?

And the answer is: it’s only your parents. If we can get the data, it’s only your parents that matter. Another test is a genetic explanation would say that any elite group that only intermarry internally would not actually regress to the mean. Because, the genetic information is not being lost from that group. And that, again, we can test by looking at various examples. And what we find then is that in societies with a high degree of endogamy, the rate of social mobility doesn’t seem to slow down. Another interpretation here would be that any elite group would simply have been selected from a larger population by some mechanism – or any underclass group. And we again can test this by looking at history and saying for example: Ashkenazi Jews are elite; Sephardic Jews are elite. Are they a subset of a larger population? And the answer overwhelmingly and very clearly is yes. Only a small fraction of the original Jewish population has survived as Jewish. The rest converted to Christianity. And, there’s very strong evidence that that was the elite share of the population.

And, we can also see in modern America that new social elites are actually being formed by immigration policy which means that people coming from areas distant from the US, without familial connections to the US, are being drawn from very high-level elites in those societies. So now, the super-elites in the US are Coptic Christians; Indian Hindus; Iranian Muslims; Maronites. And when you look across those groups, what you see is – culturally – an incredible diversity. The only groups that are not represented now in the modern US elites are protestant Anglo-Saxons. (Laughs.) So what you actually see when you look at this data, it seems to me, is that eliteness has nothing to do inherently with culture; it’s to do with the familial transmission of abilities.

Homicide Rates by Genetic versus Stepfathers

Sunday, April 6th, 2014

Homicide rates by genetic versus stepfathers and by age of child for Canada, reprinted from Daly and Wilson (1996):

Homicide Rates by Genetic vs. Stepfathers

Twin Studies

Thursday, April 3rd, 2014

In lieu of kidnapping twins, Dalton Conley explains, the way that researchers typically calculated how much a given trait — be that extraversion or earnings — was due to genetics was by comparing how alike identical twins were with respect to how alike (same sex) fraternal twins were: 

The logic is that the fraternal twins share half their genes on average and the identical twins share all of them, so the degree to which identical twins are more alike than their fraternal counterpart pairs reflects the genetic contribution to that trait.

If two-thirds of our kids’ chances in life were due to their family background, the field of behavioral genetics would have us believe that the vast lion’s share of that predictive power of family of origin was due to genetics.  According to these studies, about half of the variation in incomes or job situations was due to our genetic makeup.  And only about a sixth resulted from the household environment on which parents could exert some conscious influence.  The remaining one-third was a product of random events outside a family’s control: an inspiring teacher, a traumatic accident, or a lucky break at work.

I initially went into the field of genetics to prove these researchers wrong.  Genes couldn’t matter that much, I figured.  It just didn’t jive with what I saw around me: Siblings seemed so different from each other; I knew plenty of poor kids growing up that I could have imagined achieving great heights had they been reared in better circumstances; and, likewise, in my adulthood I had gotten to know plenty of folks who seemed to be of mediocre talent despite their huge paychecks.  Social environment had to count for more.  So I decided to go right after the geneticists’ core assumption.

That is, their nifty little calculation relies on one hugely problematic assumption known as the “equal environments assumption.”  Put in English, these researchers had to take as a given the notion that identical twins are not treated any more similarly to each other than fraternal twins are (and that identical twins don’t interact with each other more than fraternal twins do in ways that might affect the outcomes in question — i.e. that their mutual, reciprocal influence is no different than that of same gender fraternal twins).  Since in my own experience I often couldn’t even tell who was who in an identical twin set, it seemed obvious to me that identical twins were experiencing much more similar environments than fraternal twins were in ways that were not generalizable to us non-twins in the population, and thus the behavioral geneticists were inflating the effects of genes and correspondingly underestimating the impact of family environment.[2]

Determined to prove them wrong and save the day for social scientists, I thought of a trick that would have been unimaginable before the days of 23andme and the like: I would take the fraction of twins who thought they were identical when they were really fraternal (and vice versa) and run the same analysis on them.  If they thought they were fraternal twins their whole lives but the laboratory genetic test revealed they were actually identical, we could be sure that they weren’t raised with more similar environments because they had been (mistakenly) socialized as fraternal twins.  And ditto in reverse.  But when I ran these folks through the statistical models, the results didn’t refute the behavioral geneticists at all.  In fact, my models confirmed the high genetic heritability for everything from height to high school GPA to ADHD.

Group Size

Monday, March 31st, 2014

An architect by training, then a professor at Arizona State University, and now a business strategy consultant, Kristine Woolsey studies the impact of the physical environment on human behavior:

Numerous anthropological studies show that group size — the number of individuals who live or work together — is key to peaceful collaboration in all kinds of environments. The ideal group size for forming bonds of trust is around six to eight people, Woolsey said.

A gang of four can be easily dominated by one strong personality; any larger than eight, and they’ll to need to elect a leader. But right in the middle, there’s “a sort of peer pressure in terms of expected social behavior” that leads people to act in the common interest, she said.

Effective open-plan offices, such as the ones Google Inc. has designed in Zurich and Dublin, and the ones offered by NextSpace, a California-based company that rents workspaces to freelancers and small businesses, place employees in hubs of six to eight, with nearby common areas accessible to several groups, Woolsey said. Thus, rather than dividing up a giant workforce into “acres of gray cubes,” the office is instead comprised of small groups nested within larger ones.

[...]

Jeremy Neuner, the CEO of NextSpace, said he’s observed that workers naturally congregate in groups of six to eight. Recently at the company’s Santa Cruz headquarters, as a sort of experiment, a 12-seat conference table was moved into an open area of the office. Sure enough, Neuner said, six to eight people gathered there to work.

“Except when they’re up against a deadline, people are not looking for their own closed-in spaces,” Neuner said.

As Woolsey sees it, the traditional open-plan office is no better at adapting to the way people work than the old cubicle-dotted office.

How Athletes Use Caffeine

Tuesday, March 25th, 2014

Athletes use caffeine strategically:

In 2009, Ganio and his colleagues published a systematic review of 21 studies on caffeine in timed performance. Most of the researchers looked at subjects cycling, but some also studied running, rowing, and cross-country skiing, and most of the tests were in the 15-minute to two-hour range. Looking across all the results, Ganio found consistent improvements in performance.

The improvements can be substantial, he told me, often as much as 3 percent. To put that into context, a 3 percent improvement would mean an 18-minute boost in a 10-hour race. Eighteen minutes was all that separated the top eight finishers in both the men’s and women’s pro races at Kona.

[...]

Ganio said it is important to take the right dose, which shakes out to about three to six milligrams per kilogram of body mass. That is a lot of caffeine. An 80-kilo (176-pound) athlete taking six milligrams per kilogram would need 480 milligrams of caffeine.

“That’s four strong cups of coffee,” said Ganio. “If you can tolerate it, it seems to be the upper end of what you can have to improve performance.”

Since “cups of coffee” is a notoriously imprecise measure of caffeine, it may help to think of it this way: 480 milligrams would be six 8-ounce Red Bulls, two and a half NoDoz tablets, or two Extra Strength 5-hour Energy shots. A more moderate dose for a smaller athlete, say, a 65-kilo (143-pound) athlete taking three milligrams per kilo, is still an impressive amount of caffeine: equal to one NoDoz tablet, one 5-hour Energy shot, or two and a half Red Bulls. Even this amount of caffeine is difficult to obtain using caffeinated sodas like Coca-Cola. A 65-kilo athlete would need to chug nearly six cans of Coke at once to get a caffeine dose of three milligrams per kilogram.

Also, researchers found no evidence of dehydration from using caffeine.

Personality Predicts Social Learning

Wednesday, March 19th, 2014

Researchers conducted a three-year study of how personality interacts with social learning — in wild baboons in Namibia:

Carter and her colleagues had given all the baboons “personality tests” to measure two traits, boldness and anxiety. They assessed boldness by looking at a baboon’s response to a new food (such as a hard-boiled egg dyed green); the bolder the individual, the more time he or she spends inspecting a new food. They assessed anxiety by presenting the baboons with a taxidermied venomous snake; in this test, more anxious individuals spend more time investigating the potential threat. Boldness and anxiety are stable personality traits and are independent in baboons, meaning a bolder baboon is just as likely to be anxious as a shy baboon.

After figuring out where individual baboons fell on these two personality traits, the researchers looked at whether the traits were related to the time spent watching a demonstrator or the subsequent ability to then solve the task being demonstrated.

They found bolder and more anxious individuals were more likely to learn about a novel foraging task from another baboon — despite the fact that shy baboons watched the demonstrators just as much as bold baboons, and calm baboons paid even more attention to the demonstrators than anxious baboons. This means that an individual’s ability or interest in watching a demonstrator does not necessarily translate to then solving the task. All personality types seemed to collect social information, but bolder and more anxious baboons were better at using it.

Carter thinks that bold baboons may show more social learning not because they are smarter or better at learning this type of information, but because they are more willing to interact with something new. “I imagine that watching another individual manipulate a novel food requires less boldness than manipulating a novel food directly,” she says. “It’s likely the shy baboons were just too shy to handle the food, even after watching a demonstrator.”

Derbyshire on Wade’s A Troublesome Inheritance

Friday, March 14th, 2014

There is nothing breathtaking in New York Times science writer Nicholas Wade’s Troublesome Inheritance, John Derbyshire says — if you already frequent websites like VDare, InfoProc, hbdchick, or West Hunter:

Most people don’t visit these websites, though, and are raised and educated taking the SSSM [which declares race to be a “social construct”] for granted. To them, the facts that Wade’s book presents and the ideas it discusses will come as thunderclaps.

This is the “shocking” keynote of the book:

New analyses of the human genome have established that human evolution has been recent, copious, and regional.

Yosemite Bears and Human Food

Wednesday, March 12th, 2014

Researchers performed isotope analysis of hair and bone samples to study Yosemite bears’ changing diets over the past century:

Yosemite National Park was established in 1890, and Hopkins obtained samples from bears killed between 1915 and 1919 to represent the earliest time period. In those early years, bears were attracted to garbage dumps in the park and were often killed when they became a nuisance. Visitors liked to see bears, however, and in 1923 the park began intentionally feeding bears where visitors could watch them. The last artificial feeding area closed in 1971. There was also a fish hatchery in Yosemite Valley, from 1927 to 1956, where bears once helped themselves to fresh trout from the holding tanks. But closing the hatchery and the feeding areas didn’t stop bears from eating human food.

“The bears just went back to the campgrounds and hotels and continued to find human food,” Hopkins said.

The average figures for the proportion of human food in bear diets during the four time periods in the study were 13 percent for the period from 1915 to 1919; 27 percent for 1928 to 1939; 35 percent for 1975 to 1985; and 13 percent again for 2001 to 2007.

These results are based on a kind of chemical forensics in which Koch’s lab specializes. Isotopic analysis of an animal’s tissues can yield clues to its diet because of natural variability in the abundance of rare isotopes of elements such as carbon and nitrogen. Isotope ratios (the ratio of carbon-13 to carbon-12, for example) are different in human foods than in the wild plants and animals that black bears naturally eat in Yosemite, partly due to the large amounts of meat and corn-based foods in our diets.

In order to analyze the data from Yosemite bears that ate a mixture of human and natural foods, Hopkins had to get samples from bears that did not eat any human food, and he had to track down samples of the non-native trout that had been raised in the hatchery. He also needed data representing a 100 percent human food diet, for which he turned to the Smithsonian Institution for samples of human hair from different periods over the past century.

“He searched far and wide to get the collection of samples we analyzed, and that collection made the study powerful enough to answer the question of how management practices affect bear diets,” Koch said.

According to Hopkins, the key to managing bear problems is to prevent bears from becoming conditioned to eat human food in the first place.