July 27, 2012
July 18, 2012
A couple months ago Mike Martin wrote about the strange story of untrained evolutionary biologist Margie Profet and her disappearance. It was only because of its publication that Profet became aware her family was looking for her and reunited with them, and good thing they were since she had been living in poverty and with ailments as yet unrevealed. I’m sure Martin feels some warm fuzzies that his work had a positive impact (an on rather short notice too), but as a member of the younger generation it seems somewhat ridiculous that should be necessary. Shouldn’t anybody be able to set up a free email account they can access from a public library or something? And I guess there’s that Facebook thing if you’re into that. The optimal possibility from my perspective would be maintaining an open-comments blog about evolved defenses against pathogens, which I’d read even (or especially) if she was crazy.
July 1, 2012
I’ve finally read a book by Carl Zimmer, after seeing his (and his brother’s) byline on numerous pieces online. For some reason I thought he had also written “Survival of the Sickest”, but that’s apparently by somebody whose name rings no bell. Much of the book is sort of a complaint that people haven’t found parasites very interesting even though they really really are (did you know that most species of animal are parasites? I didn’t), but I’m going to write about that things that stuck in my head rather than what Zimmer may have wanted to emphasize.
Bit one is that the term “parasite” is not used to apply to everything occupying what we might call the parasitic ecological niche. Only eukaryotes & multicellular organisms are given the name, for reasons of historical accident rather than because it carves reality at the joints. Zimmer says this lead to parasites being neglected by scientists, because europe is more afflicted by bacteria & virii while tropical reasons have “parasites” proper. This made me wonder why that was the case. The classic explanation for the prevalence of tropical disease is that many species have to live in water (it is useful for carrying in nutrients and carrying out waste) and warmth is also better for most life than cold. But I would think that would apply especially to single-celled organisms (and eukaryotes admittedly qualify), while colder weather is associated with larger size. I mentioned earlier William McNeill’s claim that microparasites result in less selection for IQ relative to macropredation, and it occurs to me that a number of the macroparasites in the tropics actually should be visible without a microscope. But perhaps the overall fitness cost from all entities in the “parasite” ecological niche is still lower in northern europe.
Continuing on with the eukaryotic distinction, Zimmer argues that such parasites are more likely to manipulate their host than bacteria/virii. The reasoning seems to be that many “parasites” proper need multiple hosts for the different generational stages of their life cycle (the different forms generations can take made it difficult to tell at first different organisms were one species and satisfy Koch’s postulates, I was surprised to learn that Plasmodium have a sexually reproducing generation inside mosquitoes since they are single-celled). Could it also have to do with the complexity of the organism allowing for more complicated effects on a host, or am I placing too much weight on a fuzzy notion of “complexity”? At an rate, I was under the impression that a number of venereal diseases like syphilis (bacterial) affected their host’s behavior to spread more easily, as discussed in one of the chapters from “The Man Who Mistook His Wife For a Hat” by Oliver Sacks. I assume most readers are familiar with the Red Queen theory of infections giving rise to sexual reproduction, but Zimmer adds that William Hamilton & Marlene Zuk also argued that showy displays for sexual selection would be particularly common in response to “parasites” proper because bacteria/virii tend to just kill their hosts or get promptly eliminated themselves. I don’t know why one would expect that to be the case. Helicobacter pylorii and other bacteria can persist in hosts for a long time, and H.I.V is a well known persistent virus. Furthermore, one of the most well known examples of showy mate display is the peacock’s tail, which I had originally heard was supposed to be a credible signal that the peacock was not afflicted with diarrhea, which can often result from bacteria such as cholera (though I don’t know if cholera specifically is a common affliction of peacocks). (more…)