Wednesday, August 29, 2012

The Wild Life of Our Bodies

The Wild Life of Our Bodies: Predators, Parasides, and Partners that Shape Who We Are Today
© 2011 Rob Dunn
290 pages

You can take the man out of the jungle, but not the jungle out of the man. Such is the lesson of Rob Dunn's brilliantly-written The Wild Life of Our Bodies, which demonstrates to readers the ways in which interactions with other species have shaped human evolution, and the folly of our attempt to sever our ties with the natural world.

I initially thought this book was on the body as an ecosystem, host to millions of other lifeforms; some preying on us, others living in a mutualistic relationship with us, helping us to digest food in return for a roof over their little unicellular heads. That's only the start of Dunn's piece, and even there he turns expectations on our heads. Sure, we need bacteria to help digest our food -- but as it turns out, we need, or at least could use, parasites active in our system to give certain immune responses something to do. Absent of real threats, our immune system will happily turn on us, causing various diseases and disorders. We forget how utterly alien the civilized world is to bodies which evolved in the world, becoming geared to compete and strive and fight, to cope with famine and stress.

No man is an island, nor is any species.  The interactions between species -- as foes, as friends -- drive evolution, giving pronghorns and cheetahs faster legs to outrun the other, and avocado fruits larger volume to attract animals with larger appetites. Humans, in spite of our tendency to view ourselves as separate from the 'animal world', are no different in being shaped by others. Not only have our appearances changed because of relations with other species, but part of our emotional life and even our aesthetic senses have ties to ecology. Take taste, for instance: it's no coincident that fruit bearing seed ready to germinate tastes delightful, while unripe fruits -- those with seeds still readying themselves -- taste bitter. The bitterness is the plant's way of keeping hungry foragers from forcing the seeds into the world before their time. Other species have shaped not only human bodies, but human civilization -- take the lactose-tolerance that prevails in pastoral societies, and the way grasses and cattle have prospered by becoming the staple of many civilizations.

 This is popular science at its best: insightful, with lessons that apply across the whole of human existence, and enterprisingly written to boot. The implications for medicine are especially worth considering, and the book as a whole reminds of the law of unintended consequences.


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