Parasite Rex

Carl Zimmer is an important communicator of science, perhaps the most important such communicating in English, at the present time. I have read a few dozen of his articles and blogs, but had never read one of his books. Now I have. That book is Parasite Rex: Inside the Bizarre World of Nature's Most Dangerous Creatures. Here is the book's Amazon page, Kindle version.

Quick summary: Most animals, at least the vertebrates, arthropods, and molluscs, are parasitized by several other animals. (The book also considers plants a little. It says very little about fungal parasites. Zimmer couldn't cover everything.) Most biologists don't consider the effect of this massive amount of debilitating interaction nearly enough. Parasites are hard to study. They usually are hidden, and often pass through more than one host animal during their lifetime. Humans, until recently, were as prone to parasites as other animals. Some humans, in primitive conditions, still are. Even though parasites harm their hosts, they seldom kill them, at least not until they have had offspring with a good chance of reaching another host. If they did kill immediately, they would be destroying their own chances of survival.

Some interesting ideas:
There are probably more parasitic species than free-living ones.

Parasites have seldom been found as fossils, mostly because they are almost all soft-bodied.

The discovery of parasites caused some theological concerns:

Parasites seemed to arise by spontaneous generation. If God created everything in the first six days, then all organisms living now should be descendants of those first organisms, not just appearing suddenly, as it were, from nowhere. Eventually, it was shown that parasites came from previous organisms, often from their eggs.

It seemed that parasites were a dead end -- they just got into a host and died there. But a scientist named Friedrich Küchenmeister doubted that that was the full story, and found that those parasites, in at least some cases, were not dead ends. If the host was eaten, they went into a new stage of development.

"[Darwin] found that parasitic wasps are a particularly good antidote to sentimental ideas about God. The way that the larvae devoured their host from the inside was so awful that Darwin once wrote of them, 'I cannot persuade myself that a beneficient and omnipotent God would have designedly created the Ichneumonidae [one group of parasitic wasps] with the express intention of their feeding within the living bodies of Caterpillars.'"

I have posted on questions related to whether germs, and by extension, parasites, were present before the Fall.

Some parasites can control the gene activity of their hosts, or control the behavior of their hosts, in bizarre ways, generally to the benefit of the parasite, usually somehow helping the parasite to reach another host animal. To put it another way, they create zombies.

Parasites may be responsible for the development of sex and mating. (It is, of course, possible for many animals to reproduce without sex, although most vertebrates require some sort of fertilization to reproduce.) Often, animals display to attract females. Parasite-ridden animals usually aren't as colorful, or as active, and observing these males allows females to select the more healthy and less parasite-ridden, mates, who, usually, have better genes, perhaps genes that give resistance to parasites, or genes which cause behavior which is less likely to lead to being parasitized.

 IgE, an immunoglobulin that our own bodies produce, and that causes allergies and other problems, isn't just a nuisance. For most of human history, and in many places on earth, IgE helped to repel parasites. Some experiments indicate that ulcerative colitis and Crohn's disease (an intestinal problem) can be cured by introducing parasites into the people that have these problems.

There are other fascinating ideas, and many descriptions of how parasites live, and of the scientists who have made discoveries about them, and how these discoveries came about. A fine book!

Thanks for reading!