Cells that you have today are not all the exact same cells that you had yesterday

Over time, cells age and become damaged, so your body's cells are constantly replicating, creating their own replacements

Every seven years or so, your cells have been so productive that your body has replaced every part of itself, from your eyelashes to your esophagus

The human heart renews at a rather low rate, with only 40% of all cardiomyocytes exchanged throughout life

In the brain, cell renewal can be even more leisurely. Scientists have uncovered evidence showing that some neurons in the hippocampus are renewed

Regardless of how "young" our skin, guts and liver may be, we feel older as years go by because of our biological age, Bergmann explained

Mutations can thereby accumulate and affect the life of the cell (opens in new tab) or the expression of certain genes

So even if the cells in parts of our bodies are relatively new, our aging, much-copied DNA makes us feel the weight of all those years that have passed