
Parasites may explain regional differences in intelligence - Rob-Goodier
http://www.economist.com/node/16479286
======
donaldc
When looking at correlating factors, they should also include diet. I remember
reading that some Central Asian countries, as recently as a decade ago, were
losing more than 5 IQ points on average just to iodine deficiency.

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tokenadult
Another HN participant told me about a reply to this latest paper by these
authors.

[http://blogs.discovermagazine.com/notrocketscience/2010/06/2...](http://blogs.discovermagazine.com/notrocketscience/2010/06/29/does-
national-iq-depend-on-parasite-infections-er/)

When I see gee-whiz news reports about science, even in very reputable
publications like The Economist, I think to turn to Peter Norvig's article
"Warning Signs in Experimental Design and Interpretation"

<http://norvig.com/experiment-design.html>

to evaluate the research.

~~~
bd
There is an interesting comment in the Discover post, where Carl Zimmer
(author of popular science book on parasites) points out several studies from
all around the world (Jamaica, China, Indonesia, Philippines) where they found
children got smarter after de-worming:

[http://blogs.discovermagazine.com/notrocketscience/2010/06/2...](http://blogs.discovermagazine.com/notrocketscience/2010/06/29/does-
national-iq-depend-on-parasite-infections-er/#comment-10704)

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anonymousDan
Why wouldn't it simply be the case that more intelligent societies have been
more successful at eradicating disease?

------
T_S_
My first thought: which parasites make you smarter?

~~~
misterbwong
Had the same thought, though the article says that the _lack of_ infectious
disease (parasites) would cause intelligence gain. The population of countries
where disease is less of a problem wouldn't see the same benefit...

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JeffL
The first thing I thought of is that if lack of diseases is what has been
causing the rise in intelligence, then there's likely to be a ceiling that
average intelligence will hit as countries become healthier, rather than some
mysterious force continually increasing average intelligence forever. That
makes me a little sad.

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diziet
I'm really curious as to how exactly they accounted for other factors. They
say they compared findings to other studies that looked at other possible
explanations, but quite many of them are certainly correlated if not caused by
one another.

~~~
joubert
one can deduce how two kinds of organisms have influenced each other by
studying how their respective gene pools (have) co-evolve(d)

~~~
zppx
Statically the problem that he posed is still there, what are the variables
they ignored when calculating the statistical significance of their
hypothesis? I actually read the paper, and well, it was one of the worst that
I have read in my entire life. In the end of the paper they wrote: "We are not
arguing that global variation in intelligence is only caused by parasite
stress."

So why is the point of having a research about causation when various
independent causes can exist and do not test how much the hypothetical cause
affects the causation relationship in general? Should I publish a paper on
intelligence and ice cream consumption by population in the last 50 years to
show how ridiculous the entire situation is?

Sounds like that sort of paper that someone publishes only so that his name
get cited more times.

------
ars
It's politically illegal to say that on average whites are smarter than blacks
so instead they have this little gem:

"....distance from humanity’s African homeland (novel environments could
encourage greater intelligence)...."

~~~
Ardit20
There are plenty of Blacks outside Africa and I hear that in South Africa
there are loads of whites.

~~~
ars
If you look at the data you'll notice it's very noisy. And I bet the noise is
entirely (or mostly) made up of race.

Note that one of the things they did not control for was race.

It's racist to say this, I know, and more importantly it's not nice. But if
you are going to make a study, you have to deal with reality.

Control for race, and then check the correlation with parasites.

~~~
starkfist
How do you control for race? My grandmother is Mexican. My grandfather is
German. What "race" is my mom? What about me?

~~~
ars
You do the best you can. Perfection is not required.

------
awongh
another reason to support universal health care: a smarter public

~~~
ams6110
You presume that universal health care will lead to a healthier public

~~~
Retric
It's been successful in every country that has tried it. Granted, the US has a
bad habit of poorly implemented government programs so who knows, we may be
the first exception.

PS: Medical outcomes are far more dependent on the average level of care than
the peek level of care. EX: There is a lot of evidence that the average doctor
is significantly more effective than a "high preforming" doctor that is sleep
deprived.

~~~
anamax
> It's been successful in every country that has tried it.

Doesn't that depend on the starting point? For example, NHS started during the
post WWII depression in the UK. The US isn't starting from there.

I'm trying to track down the stats, but I've heard that the US lifespan is
world-longest if you adjust for accidents and homicide, two things that aren't
affected by healthcare.

> Granted, the US has a bad habit of poorly implemented government programs so
> who knows, we may be the first exception.

The US govt gets the same amount of tax revenue per person as the "rich" EU
countries. If the benefits are less ....

~~~
kragen
> I've heard that the US lifespan is world-longest if you adjust for accidents
> and homicide, two things that aren't affected by healthcare.

Other measures of health care quality, such as infant mortality, are worse in
the US than in many other countries. So I doubt it.

~~~
miked
_Other measures of health care quality, such as infant mortality, are worse in
the US..._

Nope. The US spends far more on trying to save the lives of premature and
sickly newborns than any other country. Many these don;t make it after being
born and show up in the stats as "high infant mortality". This approach also
drives up health care costs.

One can argue (having met two crack babies that survived, I personally would
be tempted to in many cases) that US hospitals _shouldn't_ do this, but
nevertheless they _do_ do it. And it costs money and skews statistics.

I also have personally experienced health care in other countries (Greece,
Mexico, China -- where my wife was a doctor). No thanks.

~~~
kragen
_The US spends far more on trying to save the lives of premature and sickly
newborns than any other country._

[citation needed]

 _Many these don;t make it after being born and show up in the stats as "high
infant mortality"._

That's true in every country, regardless of how hard you try to save their
lives. More of them make it after being born if you try very hard to save
their lives.

 _I also have personally experienced health care in other countries (Greece,
Mexico, China_

So have I. I surely don't need to point out to _you_ , with your wide travel
experience, that not all other countries are equal. The Argentine health care
I've experienced is head and shoulders above anything I've experienced in the
US, although that's mostly because I live in the capital where things are
good.

The US's infant mortality rate is about .0063. Greece's is about .005 to .007.
Mexico's is .017 or .018. China's is about .020 to .023. Your personal
experience that care is much worse in those countries, with the exception of
Greece, supports the validity of infant mortality as a measure of care
quality; it does not undermine it.

There are around 25 countries with better infant mortality than the US, but
that doesn't include the three you listed. Several of them have less than half
the infant mortality level of the US. Have you personally experienced health
care in any of them? What was your experience?

[https://secure.wikimedia.org/wikipedia/en/wiki/List_of_count...](https://secure.wikimedia.org/wikipedia/en/wiki/List_of_countries_by_infant_mortality_rate)

I recognize that statistics do not always capture the reality of a situation.
However, in this case, I don't think it's adequate to simply deny their
validity without any evidence. (The evidence you have adduced so far, from
your personal experience, supports their validity rather than undermining it.)

~~~
anamax
> There are around 25 countries with better infant mortality than the US,

With comparable populations?

For example, Scandanavians do well everywhere. (However, the US ones do better
than the ones who didn't leave.) A population dominated by Scandanavians will
do better than one that is more "typical".

I'm pretty sure that the US healthcare system is not responsible for crank and
crack mothers, but it gets "credit" for their birth problems.

------
archer
Correlation <> causation. IMHO they should be very careful before establishing
a link between those two.

~~~
Dove
You should read the article. They considered that.

 _The correlation is about 67%, and the chance that it might have come about
at random is less than one in 10,000. But correlation is not causation, so Mr
Eppig and his colleagues tried to eliminate other possible explanations.
Previous work has offered income, education, low levels of agricultural labour
(which is replaced by more mentally stimulating jobs), climate (the challenge
of surviving cold weather might provoke the evolution of intelligence) and
even distance from humanity’s African homeland (novel environments could
encourage greater intelligence) as explanations for national differences in
IQ. However, all of these, except perhaps the last, are also likely to be
linked to disease and, by careful statistical analysis, Mr Eppig and his
colleagues show that all of them either disappear or are reduced to a small
effect when the consequences of disease are taken into account.

There is, moreover, direct evidence that infections and parasites affect
cognition. Intestinal worms have been shown to do so on many occasions.
Malaria, too, is bad for the brain. A study of children in Kenya who survived
the cerebral version of the disease suggests that an eighth of them suffer
long-term cognitive damage. In the view of Mr Eppig and his colleagues,
however, it is the various bugs that cause diarrhoea which are the biggest
threat. Diarrhoea strikes children hard. It accounts for a sixth of infant
deaths, and even in those it does not kill it prevents the absorption of food
at a time when the brain is growing and developing rapidly._

