It’s been more than a week since ABC announced that actress and model Jenny McCarthy would join their mid-day talk show, The View, but backlash against the decision continues. At the heart of the controversy is McCarthy’s anti-vaccine activism.

Scientists pride themselves on being rational, able to disagree civilly. Of course, scientists are also human, so it doesn’t always work that way. But few things spark more raw outrage than anti-vaccination rhetoric. Even climate change and evolution might have to settle for consolation prizes in this category. But why?

Dangerous Dissent

One reason, of course, is the public health impact of non-vaccination. Vaccines are a proven way to control, if not eradicate, numerous deadly diseases. Take polio, for example. Last year, the number of children paralyzed by the disease hit a record low of 223 worldwide – down from hundreds of thousands killed or paralyzed each year in the 1940s and 1950s.

But outbreaks of diseases thought by many to be things of the past still crop up in areas where vaccination rates are low. There’s currently a polio outbreak in Somalia, and Wales saw an outbreak of measles begin last November. The Centers for Disease Control and Prevention say outbreaks of whooping cough, or pertussis, remain common in the United States.

There are a variety of explanations for these outbreaks. Polio vaccination rates in Somalia have lagged due to a combination of complacency, lack of funds, and political instability. Whooping cough outbreaks may be due, in part, to the fact that the early childhood vaccine’s effectiveness wanes over time and requires a booster during adolescence.

The measles outbreak in Wales, though, is a different story. Officials there have seen a dramatic decline in the rate of childhood measles vaccination, delivered as part of the Measles-Mumps-Rubella (MMR) triple vaccine, in recent years. Many blame Andrew Wakefield and the anti-vaccination movement that his now-debunked work spawned.

Scientific Consensus and 'Funhouse Mirrors'

Here’s the quick version: In 1998, Andrew Wakefield published a study in the medical journal The Lancet claiming a link between the MMR vaccine and autism. But, over the past fifteen years, the overwhelming majority of studies have found absolutely no evidence to support that claim. Then, in 2010, an investigation by journalist Brian Deer revealed that Wakefield had distorted and faked data, and hidden financial conflicts of interest. As a result, he was struck from the UK’s medical register and the original paper in The Lancet was retracted.

And this is what gets scientists’ goats. There is a strong scientific consensus – on par with that about human-caused climate change – that vaccines do not cause autism. (Neither, incidentally, does a non-nurturing mother – one of the prevailing ideas when the disorder was first named in the 1940’s.) The primary dissenting study has been discredited and retracted – an action that comes as close as possible to removing it from the scientific record. And yet, the anti-vaccination movement keeps chugging along. In a post on NPR’s 13.7 blog last week, Adam Frank wrote:

And that is what makes the faux debate over something like climate change so painful for scientists to watch. All the years of hard work and sweat are right there in print — right there in the literature — and yet somehow the message gets distorted for reasons that have nothing to do with the effort to understand the world. It's like living in a world of funhouse mirrors.”

You could easily substitute the words “vaccines and autism” for “climate change.” Funhouse mirrors, indeed.

If the sustained anti-vaccination movement is an example of a failed lesson on the nature of scientific consensus, it also highlights the continuing march of the scientific process. When an idea is raised, it is incumbent upon the scientific community to corroborate or debunk it. And when one hypothesis is disproven, any scientist worth his or her salt moves on to consider others, until the problem at hand is solved. Indeed, there’s a saying that good science generates more questions than answers.

Real-life Medical Mystery

There is no shortage of questions about what does cause autism. Genetics certainly plays a role; on the order of one thousand regions of DNA have been linked to the disorder. But the National Institute of Mental Health estimates that genetic factors only account for 10-20% of all autism diagnoses.

The efforts of the scientific community currently are focused largely on the role of environmental factors – pollutants, medications, foods or food contaminants – that could account for the other 80-90%. Since autism shows up so early in life, most scrutiny has fallen on exposures that occur while still in the womb. One emerging area of research, though, has begun to consider the possibility that autistic children may be manifesting the effects of alterations in their mothers’ eggs wrought by chemicals to which their mothers were exposed.

It is this real-life medical mystery, and what the search for answers may teach us about the development of the human mind, that makes autism truly fascinating.