An important finding from studies in evolutionary psychology regards the instinct to avoid “contamination.” Humans avoid touching a object, and even more so, ingesting food, that is thought to be “contaminated” without regard to the ratio of “good” to “bad.” This might be considered a hard-wired version of a naive biology, which protects from dangerous pathogens in the form of replicating bacteria or parasites. The main difference between a threat of replicators as opposed to something toxic like a poisonous chemical, is that final population of replicators is not limited by their initial numbers. Rather, they will, as is their want, replicate until they reach some natural limit or resources, etc. That is why they are called “germs” (literally “seeds”). Like weeds, once one is in the garden, no part is safe. While the germ theory is disease is centuries old, more recent threats have been intensified in which the poisonous seeds are not alive in the conventionally sense. Mad Cow Disease, which is called Creutzfeldt–Jakob disease in humans, was so terrifying since it seemed to be contagious although no previously known pathogen could be identified as the cause. It turned out that a single misfolded protein called a prion was what was being passed in CJD. The misfolded protein served as a template that caused normal proteins to also misfold in the same way, creating a contagion no less real than one caused by multiplying bacteria.
Crystals can often be coaxed to form in a solution if a seed crystal is added to the mix. This helps overcome the “nucleation barrier” that causes small crystals to dissolve. However, once the crystal is large enough, the addition of new units is spontaneous. The same process causes the bubbles to float out of carbonated drinks – at least one bar advertises that their beer glasses are laser etched to help encourage the bubbles to become “nucleated.”
Kurt Vonnegut’s “Cat’s Cradle” explores a similar theme, in which the dangerous germ is a seed crystal for a more stable configuration of ice that would be solid at room temperature. If a crystal would come in contact with normal water, the whole thing would freeze solid, based on the action of the tiny seed. In real life, Tin pest is an autocatalytic form of tin that can lead to metal slowly turning to dust after being contaminated.
An important new paper shows how another condition, Alzhimer’s disease, is the result of a misfolded protein that conscripts normal proteins into its deadly game. In this case, a single misfolded protein serves as a template that grows as new proteins are added, forming a fibril. The authors of the new study were able to show that even the sides of this fibril contribute to the “secondary nucleation” of additional fibrils. In this one, a single seed of malignant protein can wreak havoc. Insights like this are crucial to efforts to stem the tide of the disease.