So, today I have lectured for five hours on the diseases of the cardiovascular system. It’s the fifth consecutive year that I have the honour of lecturing on this topic for some of the undergraduates in our department.
One aspect that I have always brought up is that heart muscle cells essentially don’t reproduce in adulthood. This is why a myocardial infarction leaves a permanent fibrous scar, that will remain for life. The heart cannot heal back to its normal functionality. And the low proliferative capacity of the heart muscle cells is probably closely linked to the strange phenomenon that they never give rise to cancer.
Alas, this has changed. A paper appeared just a few days ago from the Frisén laboratory showing that heart muscle cells do proliferate, but slowly. About half of them are replaced at some point during adulthood. The technique used to demonstrate this is based on the detection of carbon-14, levels of which increased dramatically in the entire atmosphere of the earth in the 1950’s and 60’s due to test detonations of nuclear bombs. The DNA in heart muscle cells from people who were already adults at that time was found to contain far more carbon-14 than expected, indicating that new cells had been formed.
When I was in high school, I used to wonder what it felt like to be a teacher, when old knowledge was proven false. Suddenly, I thought, a lot of past work would seem counterproductive.
But this is not how I feel at all! It’s a delightful sensation, a feeling of moving forward.
This reevaluation is a reminder that all our knowledge is provisory, and can be overturned at any time by new evidence. I shudder to think of a world where we didn’t question our old beliefs.