7.18.2006

Germs and Brains

In my last set of links I brought up Gregory Cochran's "germ theory" of disease- that many ailments we think of as primarily genetic or environmental are in fact due to infectious agents. I'd like to take this a step further, and mention a similar (yet even more speculative) theory from Agnostic over at Dusk.

While Cochran suggests germs may be the culprits behind many "lifestyle" or "genetic" diseases such as rheumatoid arthritis, Agnostic suggests that much of the variation we see in personality, motivation, and higher cognitive function also may stem from complex interactions with germs. His emphasis, specifically, is that lucky interactions with microorganisms who slip past the "gateway" into the brain, the blood-brain barrier, could be partly responsible for reinforcing certain thinking and motivational patterns common to geniuses. Newton, in short, may have had germs to thank for rearranging his brain for exceptional creativity.

This is a highly aggressive assertion. It'd be very hard to prove (or disprove) that microorganisms commonly influence higher cognitive functions, though we do have solid evidence that some germs do affect behavior (i.e. rabies and toxoplasmosis), that some germs we carry around are good for us, and that the onset of certain patterns of thinking- i.e. schizophrenia- show signs of infectious causation. These facts are somewhat suggestive of some deeper germ-brain connection.

Agnostic's argument depends upon:
  • The vast amount of germs (good and bad) that live in our body;
  • The vast possibilities of how germs could interact with cellular processes and alter mental processes, purposefully or accidentally, given that we already know some do (and that, among all these possibilities, surely a few of them involve increasing the host's intelligence, or altering their motivation).
  • A lack of alternative explanations for the numerous differences which develop between twins
  • A higher winter/spring birth percentage in the set of geniuses (and schizophrenics) he looked at, which he suggests may be indicative of a higher exposure to certain germs as susceptible newborns. The percentages are somewhat startling: he draws on Charles Murray's book "Human Accomplishment", and of the 18 top geniuses Murray identifies, we know the birth month of 16, and of these 16, all but two were born in the winter or spring.

Unfortunately, these connections between genius and infection are rather circumstantial and speculative, and this is not a very testable hypothesis. However, I think there's really something to the author's more general point, that "Of all the imaginable sources of variation in higher cognitive functioning among human beings, the one that remains the least explored is the role of microorganisms."

We know very little about these things inside of us, but we're quite aware that they're terribly important. The organisms we carry around are so tightly integrated with our bodies that we'd die if they weren't there, they outnumber our cells 10 to 1, they vary widely between individuals, many live in our brains, and, as John Hawks notes, we "are using the same metagenomic techniques to fine organisms in our bodies that are used to find new unidentified ocean life!" It would seem quite a stretch to hold that some of the organisms we carry around with us don't significantly affect our cognitive functions in some way. We're not talking "brain control by germs", but this may show up in contributing to more outliers (the Newtons and schizophrenics of this world), in increasing mental variation, and perhaps shifting certain average personalities a few points in some direction.

I think the takeaway concept from Agnostic's argument is that the microorganisms in a person's body almost certainly affect their personality, motivation, and higher-order thought-processes somehow, though we're far from understanding how they would do so, and that a lot of the variation between people may very well arise from the different germs they have, and how the complex interactions between their brains and their germs are playing out. And though it may sound creepy that germs probably commonly influence behavior, it's been this way for millions of years.

This is the first in a series which examines quirky things in and around genetics.
Epigenetics post planned for next week.

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