The Clock Inside You

There is a clock running inside every cell of your body. It has been running since before you were born. It does not tick. It does not chime. But it is keeping time all the same, and a group of researchers at Harvard have just learned to read it.

What they did, in essence, was listen to the hum of 11,000 living things. Mice, rats, macaques, humans. Tissue from 25 different parts of the body. Transcriptomes, which is the word scientists use when they mean the full chorus of genes singing away inside a cell at any given moment. And when they laid all of this out and looked very carefully, they found something rather wonderful: aging sounds the same in all of us.

The patterns of gene activity that change as a mouse grows old are, in their essential shape, the same patterns that change in you. Evolution, it turns out, settled on a single strategy for wearing out its creations, and has been using it loyally across 80 million years of mammalian history.

From these patterns, the team built what they are calling molecular clocks. Not chronological age, mind you, the number of times the Earth has lapped the sun since your birthday, but biological age. The real number. The one your body is quietly keeping track of regardless of what your passport says. In humans, these clocks predicted time of death with an accuracy that matched the best epigenetic tools science currently has.

Somewhere in your cells, the count is running. Now we can read it.

Which raises a question worth sitting with for a moment.

If you could find out your biological age, the number your body actually believes itself to be, would you want to know? Would you book the test, open the results, read the number? Or would you, on reflection, prefer to leave the clock face turned to the wall?

Most people, when asked in the abstract, say yes. Of course they would want to know. Knowledge is power. Forewarned is forearmed. All of that.

But the abstract has a way of feeling quite different once it becomes an envelope on the kitchen table.