Currently I’m reading The Hidden Life of Trees by Peter Wohlleben, a collection of jaw-dropping facts about trees. I may blog about it some day, but I don’t think most of you would believe me. Today I am thinking about an ancient spruce in Sweden whose root was determined to be 9,550 years old.

The root of a tree is its most permanent part, and the closest thing it has to a brain in terms of centralized control, retention of learning, and coordinated communication with other plants and fungi. (I know, I just said you wouldn’t believe it.) This particular tree has been chopped down, or struck down, or eaten by insects, or otherwise reduced to stump level many, many times; its above-ground portion is much younger. But the root has been alive continuously.

Many trees are able to regrow from stumps, which leads to the question of identifying an individual tree. Is it the part we see, or the part underground? If it’s the combination, how does it decide which birthday to celebrate?

During docent training I studied the life cycle of the moon jelly, a shape shifter. The adults reproduce sexually. The larvae are microscopic, ciliated swimmers. After a few days they attach to something and become polyps, stems with tentacles on top, tiny but visible to the naked eye. Those can live for 25 years, and during that time they create colonies of clones.

At least once a year, each polyp’s upper body transforms into a stack of about 25 tentacled disks which break off one by one, swim away, and eventually grow into adult moon jellies. This is an animal that would be hard-pressed to identify its forebears. The population probably doesn’t have much trouble with the It’s all about me! attitude though.

As humans, most of us can identify our forebears, and point to pictures of ourselves stretching back at least to birth. But are they all the same person? Not in a literal sense, since we replace cells constantly. Even neurons in the brain, once thought to be unchanging in adults, now are believed to be replaceable.

Then there’s our microbiome. Each of us has about as many bacterial cells as human cells in our body, which comprise much less than half of the volume but much, much more than half of our genes: 30 to 500 times as much. These biota have a huge impact on our lives, controlling everything from our immune systems to our food cravings.

I read once about an adult man who developed pedophilia because of the location of a brain tumor. His predilection for it disappeared when the tumor was reduced by treatment and reappeared when it regrew. In this case a disease vector fundamentally altered his identity in a super-creepy way.

Have any of you ever been confronted with irrefutable proof that something you believe you experienced actually never happened? It’s startling. Perhaps this will happen more as the record-and-publish-everything generation ages. Or perhaps this generation will avoid confirmation or consistency bias since so much evidence is extant.

That seems unlikely.