After my father died last year of pancreatic cancer at 72, I found myself thinking about a question that's easy to avoid when you're healthy: How much of my future is already written into my biology? To find out, I enrolled in an executive health program at Human Longevity, a Silicon Valley clinic that combines full-body imaging, blood testing, and genomic sequencing to assess health risks and longevity. In total, the tests cost about $12,000. What I learned was both reassuring and unsettling.