Pen drawing
Professor Shinya Yamanaka
I learned a lot from a YouTube conversation with Professor Yusuke Narita and Professor Shinya Yamanaka. All the cells in the human body are replaced except for two parts. The only parts that remain unchanged are the cells in the brain and heart.
I also learned in the process of iPS cell research that living things originally had the ability to regenerate. I think this ability gradually disappeared to avoid the risk of cancer. Even today, geckos have amazing regenerative abilities and can regrow their legs even if they are cut off. They even regenerate bones. Speaking of which, I think that the replacement of human teeth from child teeth to adult teeth is also a form of regeneration.