It Takes a Genome: How a Clash Between Our Genes and Modern Life Is Making Us Sick

Imbalance of the Immune System

The wonder with all of these diseases is not so much that they happen, but that severe forms afflict only a few percent of us. As with cancer and diabetes, we’re dealing with an extremely complex genetic system in a species that has done an awful lot of evolving recently, in an environment that is fundamentally foreign with respect to most of our history. The question, “Why are there genes for arthritis?” is as misplaced as asking, “Why are there soldiers who fire on their own?” They don’t mean to; it just happens.

Let’s consider the complexity first. All organisms face a bewildering array of microscopic enemies. Belligerent bacteria, vile viruses, and pesky parasites confront the immune system with different challenges ...