You are what infests you—and that’s not all bad, declares Zuk (Biology/UC-Riverside).
This latest take on the hot field of evolutionary biology reviews scores of studies to suggest that all creatures great and small have always had to contend with parasites that need to live on the rest of us. As a result, we have co-evolved, honing our immune systems to control them, even as the bugs develop countermeasures. So don’t even think of trying to sterilize everything around you; those very antibacterial potions may have contributed to the explosion of allergies and asthma as the immune system, lacking its normal stimuli, latches on to pollen or other innocuous matter. Feeding sterile worm eggs to patients with Crohn’s disease has actually caused remissions, Zuk reveals, presumably because the immune system targets the eggs rather than becoming hyperinflammatory. And sex may have arisen because the gene mixing when sperm meets egg improves our immune defenses. Moreover, the author cites studies to suggest that when females choose the big antlers or the brightest coxcombs, it’s because they read those as signs of a healthy male; testosterone actually suppresses immunity, so he has to have a really good defense system to start with if he is to invest in all that showmanship. Later chapters present fascinating material on how parasites can alter hosts’ behavior, e.g., the spider that spins a tent to cocoon its infested wasp larva, along with speculation that humans may show personality changes from parasitic effects on the brain. As new diseases like AIDS and SARS emerge, and old diseases like tuberculosis stage a comeback, the author reminds us not to put all our faith in antibiotics, given bacteria’s effectiveness in developing resistant strains.
Sure, some of this is over the top, and Zuk is certainly not arguing against sanitation, clean water, vaccines and drugs. But her basic point—that parasites will always be with us and not always against us—is well taken.