“Life is mostly an exercise in being something other than what we used to be while remaining fundamentally — and sometimes maddeningly — who we are,” Meghan Daum wrote in her unforgettable meditation on what makes us who we are.

I thought of this recently when I returned to my alma mater to deliver the 2016 commencement address. The evening before the ceremony, I wandered through campus — the alleys I had once walked daily, the library unchanged by the lapse of a decade, the tree under which I gave up reading Ulysses. I found myself puzzling once again over the paradoxical continuity of personal identity — what is it that makes the me of today the same person as the young woman who walked those passageways a decade ago? I look different, I value different things, my life is entirely different and unlike anything she could have possibly imagined, my body has healed. Even my hair has changed color and texture by its own accord.

What, then, makes us ourselves?

That question, or at least the biological aspect of it, is what Lulu Miller, co-host of NPR’s ceaselessly excellent Invisibilia, posed to NPR’s Adam Cole. His fascinating answer presents a kind of bodily Ship of Theseus, exploring the rate at which your body — the amalgamation of organs, tissues, and other structures comprising the physical you — renews itself:

In a fantastic related episode, Invisbilia explores the psychological counterpart to this biological perplexity and examines the myth of fixed personality, reaching the same conclusion that Anaïs Nin did many decades earlier in her magnificent defense of the fluid self.

Complement with Grace Paley on the art of growing older, psychologist Carol Dweck’s pioneering work on fixed vs. growth mindset, and the trailblazing Harvard psychologist Jerome Bruner, whose body recently ceased renewing at the age of 100, on how storytelling shapes our sense of personhood.