Revealing the facts

There are several science myths that still hold ground. Megan Scudellari takes a look at the popular ones and demystifies them

Some dangerous myths get plenty of airtime — vaccines cause autism, HIV doesn’t cause AIDS. But many others swirl about, too, harming people, sucking up money, muddying the scientific enterprise — or simply getting on scientists’ nerves. Here, we look at the origins and repercussions of four myths that refuse to die.

Screening saves lives from cancer

Regular screening might be beneficial for some groups at risk of certain cancers such as lung, cervical and colon, but this isn’t the case for all tests. Still, some patients and clinicians defend the ineffective ones fiercely. The belief that early detection saves lives originated in the early 20th century, when doctors realised that they got the best outcomes when tumors were identified and treated just after the onset of symptoms. 

The next logical leap was to assume that the earlier a tumor was found, the better the chance of survival. “We’ve all been taught, since we were at our mother’s knee, the way to deal with cancer is to find it early and cut it out,” says Otis Brawley, chief medical officer for the American Cancer Society.

But evidence from large randomised trials for cancers such as thyroid, prostate and breast has shown that early screening is not the lifesaver it is often advertised as. For example, a Cochrane review of five randomised controlled clinical trials totaling 3,41,342 participants found that screening did not significantly decrease deaths due to prostate cancer.

“People seem to imagine the mere fact that you found a cancer so-called early must be a benefit. But that isn’t so at all,” says Anthony Miller at the University of Toronto in Canada. Miller headed the Canadian National Breast Screening Study, a 25-year study of 89,835 women aged 40–59 years old that found that annual mammograms did not reduce mortality from breast cancer.

That’s because some tumors will lead to death irrespective of when they are detected and treated. Meanwhile, aggressive early screening has a slew of negative health effects. Many cancers grow slowly and will do no harm if left alone, so people end up having unnecessary thyroidectomies, mastectomies and prostatectomies. Antioxidants are good and free radicals are bad.

In December 1945, chemist Denham Harman’s wife suggested that he read an article in Ladies’ Home Journal titled ‘Tomorrow you may be younger.’ It sparked his interest in ageing and years later, as a research associate at the University of California, Berkeley, Denham had a thought “out of the blue,” as he later recalled.

Ageing, he proposed, is caused by free radicals and reactive molecules that build up in the body as byproducts of metabolism and lead to cellular damage. Scientists rallied around the free-radical theory of ageing, including the corollary that antioxidants, molecules that neutralise free radicals, are good for human health.

By the 1990s, many people were taking antioxidant supplements such as Vitamin C and beta-carotene. It is “one of the few scientific theories to have reached the public — gravity, relativity and that free radicals cause ageing, so one needs to have antioxidants,” says Siegfried Hekimi, a biologist at McGill University in Montreal, Canada.

Yet in the early 2000s, scientists trying to build on the theory encountered bewildering results — Mice genetically engineered to overproduce free radicals lived just as long as normal mice and those engineered to overproduce antioxidants didn’t live any longer than normal.

It was the first of an onslaught of negative data, which initially proved difficult to publish. The free-radical theory “was like some sort of creature we were trying to kill. We kept firing bullets into it, and it just wouldn’t die,” says David Gems at the University College London, who started to publish his own negative results in 2003.

Then, one study in humans showed that antioxidant supplements prevent the health-promoting effects of exercise, and another associated them with higher mortality. None of those results has slowed the global antioxidant market, which ranges from food and beverages to livestock feed additives. “It’s a massive racket,” says David, “The reason the notion of oxidation and ageing hangs around is because it is perpetuated by people making money out of it.”

Humans have exceptionally large brains

The human brain — with its remarkable cognition — is often considered to be the pinnacle of brain evolution. That dominance is often attributed to the brain’s exceptionally large size in comparison to the body, as well as its density of neurons and supporting cells, called glia. None of that, however, is true.

“We cherry-pick the numbers that put us on top,” says Lori Marino, a neuroscientist at Emory University in Atlanta, Georgia. Human brains are about seven times larger than one might expect relative to similarly sized animals. But mice and dolphins have about the same proportions and some birds have a larger ratio. “Human brains respect the rules of scaling. We have a scaled-up primate brain,” says Chet Sherwood, a biological anthropologist at George Washington University in Washington DC.

Even cell counts have been inflated — articles, reviews and textbooks often state that the human brain has 100 billion neurons. More accurate measures suggest that the number is closer to 86 billion. That may sound like a rounding error, but 14 billion neurons is roughly the equivalent of two macaque brains.

Human brains are different from those of other primates in other ways: Homo sapiens evolved an expanded cerebral cortex — the part of the brain involved in functions such as thought and language — and unique changes in neural structure and function in other areas of the brain.

The myth that our brains are unique because of an exceptional number of neurons has done a disservice to neuroscience because other possible differences are rarely investigated, says Chet, pointing to the examples of energy metabolism, rates of brain-cell development and long-range connectivity of neurons. “These are all places where you can find human differences, and they seem to be relatively unconnected to total numbers of neurons.”

Individuals learn best when taught in their preferred learning stylePeople attribute other mythical qualities to their unexceptionally large brains. One such myth is that individuals learn best when they are taught in the way they prefer to learn.

There are two truths at the core of this myth: Many people have a preference for how they receive information, and evidence suggests that teachers achieve the best educational outcomes when they present information in multiple sensory modes. Couple that with people’s desire to learn and be considered unique, and conditions are ripe for mythmaking.

“Learning style has got it all going for it: a seed of fact, emotional biases and wishful thinking,” says Howard-Jones. “What you prefer is not always good for you or right for you,” says Paul Kirschner, an educational psychologist at the Open University of the Netherlands.

In 2008, four cognitive neuroscientists reviewed the scientific evidence for and against learning styles. Only a few studies had rigorously put the ideas to the test and most of those that did showed that teaching in a person’s preferred style had no beneficial effect on his or her learning.

The human population is growing exponentially

Fears about overpopulation began with Reverend Thomas Malthus in 1798, who predicted that unchecked exponential population growth would lead to famine and poverty. But the human population has not and is not growing exponentially and is unlikely to do so, says Joel Cohen, a populations researcher at the Rockefeller University in New York City. The world’s population is now growing at just half the rate it was before 1965.

Today there are an estimated 7.3 billion people and that is projected to reach 9.7 billion by 2050. Yet, beliefs that the rate of population growth will lead to some doomsday scenario have been continually perpetuated.

Like others interviewed for this article, Joel is less than optimistic about the chances of dispelling the idea of overpopulation and other ubiquitous myths, but he agrees that it is worthwhile to try to prevent future misconceptions. Many myths have emerged after one researcher extrapolated beyond the narrow conclusions of another’s work, as was the case for free radicals.

Beyond that, it comes down to communication, says Paul Howard-Jones, professor of neuroscience and education, Bristol University. Scientists need to be effective at communicating ideas and get away from simple, boiled-down messages.