Every day, an all new you

We are always changing. Literally. In a region of the brain called the hippocampus, about 3 percent of neurons are replaced each month. Red blood cells get a little overripe after a few months in service and are trashed in favor of new ones. Proteins have a shelf life, after which they are degraded and new copies are substituted. You'd be hard-pressed to find a single molecule in your body that was there at birth.

This unsettles me - the idea that the me sitting here is destined to be reconstituted with all new molecules. It would probably unsettle anyone. On a psychological level, we are all resistant to the inevitability of change, all biased to believe that what is, will always be. This isn't just an academic concern; it's pertinent to the new world dawning in a few weeks.

If you carry out a "longitudinal" study - follow your subjects for decades, as scientists have done - and, at various points, assess their personalities and values, you'll find that there's a steady rate of change throughout. We're all constantly evolving. Then try asking your subjects a retrospective question: How much has your personality changed in the last decade? What about your values? From teenagers to grandparents, people give relatively accurate assessments.