Dear Ines,

I have gray fur. But sometimes I think it’s getting grayer—like my human friends’ hair does as they get older.

I asked my friend Jiyue Zhu about that. He’s a biochemist at Washington State University.

He told me it’s a mystery.

“We still don’t completely comprehend this,” Zhu said. “It’s an active area of research.”

Aging seems to be related to the way cells duplicate.

DNA is a set of instructions for making your body. You keep a copy of your DNA folded up inside each of your cells.

All those cells have different life spans. Some, like your skin cells, … » More …

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