prions, mad cows and memes

Years ago, when I was in school, there were two sources of transmissible disease: bacteria an viruses. This idea was so well entrenched that it was very hard to suggest that there might be a third category. Of course, congenital disease and poisons cause disease, too, but these are nottransmissible. In the last 10 years, a new kind of disease-causing element was isolated: the prion. Even 5 years ago it was a contentious issue, but my sense of the landscape is that the consensus has been reached: there are proteins that mis-form and then cause other proteins to mis-form.

It’s known that these proteins get from one animal to another through cannibalism. If a mad cow eats another mad cow, it spreads the disease. How the mis-folded proteins get from the gut to the brain remains a mystery as best I have heard. I’d be really interested to learn of new findings in that area. In any case, there were some rumors in 2004 that there might be a more virulent form of prion disease in caribou, but I never heard any more about it. Interesting trivia, prions and some spider silk proteins are both amyloids.

I ramble on about this to illustrate a point: extremely unlikely things (flukes) can have a strong impact if they are in an environment that is “propagative”. I’ll illustrate with a flower analogy then talk about prions again. Let’s say I have a hundred acres of fresh, beautiful, irrigated, tilled soil. It’s ready for seed, but it’s in the middle of a desert and there are no seeds. It’s isolated. The event of a single seed (the size of a grain of sand) falling in that huge hundred acres would be impossible to notice. If you looked for seeds with a magnifying glass, you could look for your whole life and never see one land. But if you just wait and look for flowers, you have a much better chance of inferring that a plant has landed. Probably if a seed lands you won’t notice. You might not even notice the first plant. But given a few growing seasons, you will see a whole patch of earth covered with all of that one seed’s great grandchildren. The event was rare, but its consequences grow very quickly in that fertile ground.

Now let’s return to prions. The seed is a single protein molecule mis-folding. It causes other proteins to mis fold. That means that the fertile ground upon which this seed has fallen is the cow’s brain. And the plant that grows is madness. If cow’s brains are isolated, that’s not a big deal for anyone but that cow. But if the cow’s brains are brought into proximity to other cow’s brains, then that one seed (no matter how rare) will take up the whole space eventually.

Eventually, I’d like to talk about memes on this space. Memes are like flowers and prions and seeds. Given fertile space, they spread. The consequences of that are entirely dependent on the type of meme. Some are beneficial and some are detrimental; some are slow to grow while others spread quickly. They are ideas that jump from one mind to another. As humans, we can choose the memes for which we make our minds a habitat. That is one of our greatest gifts.

More to come.

-Peter