(Parts II, III, & IV to follow, will focus respectively on definining genius / creativity, how a germ could contribute to genius, and evidence for genius germs by examining winter-spring seasonality of births of the giants among giants in scientific & artistic fields.)
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. Consider the gut flora: in the gut alone there are 10 times as many microbes as there are cells in the human body (10^12 human cells * 10 = 10^13 gut microbes), which represent some 100s of species. Some of them are parasitic: indeed, the 2005 Nobel Prize in Physiology or Medicine was awarded to Barry Marshall & Robin Warren, two Australian doctors who proved that the helicobacter pylori bacterium causes much of gastritis and stomach ulcers, despite conventional medical wisdom that they were due to genetic profile and/or diet & lifestyle, a vindication of Paul Ewald & Gregory Cochran's new germ theory (click first item of this for the pdf). Of course, gut flora also contain species that benefit us, not out of sheer kindness, since the stuff we can't digest is food for them. Because we have no clue what most species in the gut are doing, only further research can resolve the ratio of parasitic to mutualist bugs.
So they're in our colon -- are they in our brain, too? If you took a neuroscience class or read a few popular articles on it, you might remember that we have what's called the Blood-Brain Barrier (BBB), a very narrow passage from the bloodstream to the nervous system which protects the brain by only allowing in a tiny range of molecules, like a sieve, unlike the more open passages to other organs. However, most neuroscientists lack a true appreciation for the role of evolution, for once we observe a neurological Wall of Troy, it's clear enough to anyone that it acts as a gatekeeper, but it should also be clear that this, like any defense such as the skin & nose hair, is the hallmark of an evolutionary arms-race -- in this case against living things small enough to pass into the bloodstream: microbes. Because the latter are also evolving (unlike the rain & dirt that our skin keeps out), and much faster than we are, all they need is to stumble upon a mutation for smaller size to squeeze through, or evolve a neurological cannon to blast through our Wall; or perhaps a neurological Trojan Horse would suffice. We would then evolve a better Wall, and the cycle would repeat. Our BBB is not unique in the animal world: it protects the nervous systems of vertebrates and insects, a testament to the ubiquity and eternity of the struggle against pathogens. See my previous post here on the recent Wang et al. paper which showed that among the genes that have undergone rapid recent selection in humans are ones that have to do with pathogen response and neuronal function.
The brain uses up 20% of the body's energy, so that's quite a hot spot to hit if you're hungry. More, if the human host is a mere vehicle to transport you to the real host, you want to get your hands on the main control levers to get you there. Homo sapiens have inhabited the Earth in their roughly modern form for ~500,000 years, always swarmed by varying degrees of bugs, so the odds that zero of them have shrunken themselves or stumbled upon a cannon or Trojan Horse to bypass our most recent version of the Wall is -- well, about nihil. To name just a few obvious culprits, with presumably many more unidentified: the neurological symptoms of African sleeping sickness result from the protozoa Trypanosoma brucei crossing the BBB; in people with compromised immune systems (mostly from AIDS), the common JC virus cannot be held in check and is free to cross the BBB, causing progressive multifocal leukoencephalopathy (PML); and bacterial meningitis seems to use a Trojan Horse strategy to cross the BBB of newborn infants. So, right after you're born, the bugs are already digging in, and they never leave you alone. As an aside, the nucleus affected in gay men and sheep belongs to the hypothalamus, a part of the brain which lacks a BBB. Also, any drugs designed to act on the brain bypass the BBB directly or indirectly.
It's easier to recognize when things are screwed up than when they're working normally, so we mention the evidence above only to show that in the evolutionary arms-race, the bugs (not surprisingly) have figured out how to bypass our latest version of the Wall. In principle, more difficult to detect flora could be doing so in order scratch our back if we scratch theirs, much as the mutualist gut flora make a bee-line for our colon not long after we're born. In the next post, we will briefly discuss how a germ could help someone become a genius.