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!

Carl Zimmer muses on parasitism

Spontaneous generation was the best explanation for parasites, given the evidence at hand. But, it was also a profound heresy. The Bible taught that life was created by God in the first week of creation, and every creature was a reflection of His design and His beneficence. Everything that lived today must descend from those primordial creatures, in an unbroken chain of parents and children -- nothing could later come squirting into existence thanks to some vital, untamed force. If our own blood could spontaneously generate life, what help did it need from God back in the days of Genesis?
The mysterious nature of parasites created a strange, disturbing catechism of its own. Why did God create parasites? To keep us from being too proud, by reminding us that we were merely dust. How did parasites get into us? They must have been put there by God, since there was no apparent way for them to get in by themselves. Perhaps they were passed down through generations within our bodies to the bodies of our children. Did that mean that Adam, who was created in purest innocence, came into being already loaded with parasites? Maybe the parasites were created in him after his fall. But wouldn't this be a second creation, an eighth day added on to the first week. . . Well, then, maybe Adam was created with parasites after all, but in Eden parasites were his helpmates. They ate the food he couldn't fully digest and licked his wounds clean from within. But why should Adam, created not only in innocence but in perfection, need any help at all? Here the catechism seems to have finally fallen apart. Carl Zimmer, Parasite Rex: Inside the Bizarre World of Nature's Most Dangerous Creatures (New York: Free Press, 2000, p. 5)

See here for Zimmer's blog.

Thanks for reading.

Parasitism, again

This is a photo of Indian Pipe, Monotropa uniflora.

Indian Pipe is a flowering plant, and there are flowers on the plant in this photo. Almost all flowering plants have chlorophyll, a green pigment. This plant does not, and it does not carry out photosynthesis. Hence, it needs to get its energy some way. The Wikipedia article on the plant says that it is a parasite, living on underground fungi, which surprised me. Fungi are often parasites on flowering plants. Well, why not the reverse, once in a while?

We found this along a hiking trail in the Beaverhead National Forest, in Montana, USA.

Thanks for reading, and looking.

Speaking of parasitism

In my previous post, I made a brief reference to a parasitic relationship. There are some really amazing, or perhaps strange, such. Here's a YouTube video, of a parasitized snail. The video is about 90 seconds in length. The parasite has changed the behavior of the snail, to the detriment of the host, but to the advantage of the parasite.

Note that if a parasite is too harmful, it will destroy it's own ecological niche -- parasites need hosts.

Thanks for reading.