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Germs of Endearment
Biologist links bacteria, our well-being in infectious read
(Headline from the Dallas Morning News)
A parasite said to its host,
"Though I am not trying to boast,
My favorite trick
Is making you sick
So your health will be better than most."
Species chauvinists beware! Your view of humanity's dominance of Earth is upside-down.
Riddled With Life, a fascinating and entertaining new book by biologist Marlene Zuk, presents an intriguing view of the factors that drive the evolution of life on Earth. She begins with a familiar premise: To be successful, a species must respond to environmental challenges. It must be able to thrive despite changes in both its physical surroundings and its ecological milieu.
Species do not simply evolve; they co-evolve with all other species in their environment. They develop some traits that are advantageous in competitions with other creatures and other traits that rely on the presence of those creatures.
The co-evolution of predators and prey, of plants and animals--even of mammals and the bacteria that colonize their guts--is unsurprising. But Ms. Zuk carries the idea further. Because humans evolved in the presence of parasites and pathogens, do we now depend on them?
Her answer is an unequivocal yes. One of the most persuasive pieces of evidence for this conclusion is the paradoxical increase in asthma, allergies, and auto-immune diseases.
"[T]he overly cleansed world into which we now proudly place our newborn babies may be a deceptive haven from illness," she writes in the Introduction. "Like bored children, immune system cells may start working mischief, attacking the cells of the very body they inhabit or initiating an elaborate assault on an innocuous pollen grain or mote of dust. Having evolved with parasites, could we suffer when they are gone?"
As the book's long subtitle suggests, this is a collection of loosely connected stories with a common theme. Readers will find surprising insights and delights in tales of "Friendly Worms, Ladybug Sex, and the Parasites That Make Us Who We Are."
They will discover that our species' strengths are intertwined with its woes, and that in the never-ending competition for Earth's resources, a little illness is inevitable. "Not Such a Bad Case" (the title of Chapter 3) may be a good thing in the long run.
Those who like a little sex to spice up their reading will find plenty of savory and unsavory questions. Did sexual dimorphism, or even sex itself, evolve in response to parasites or pathogens? Why do high levels of testosterone persist in males, even though it makes them more susceptible to disease?
The book's final chapter "Who's in Charge Here, Anyway?" is particularly provocative. Completing the life cycle of many viruses, bacteria, and parasites depends on changes in the behavior of affected hosts. Ms. Zuk cites a scientist who argues that human cultural differences may result from "longstanding differences in infection." Readers, perhaps under the control of mind-invading organisms, are willing to consider the possibility.