127 Essays on Infinite Lifespans   Marvin L. Minsky Nevertheless, we might be able to replace certain worn out parts  of  brains  by  transplanting  tissue-cultured  stem  cells. This procedure would not restore lost knowledge – but that might not matter as much as it seems. We probably store each fragment of knowledge in several different places, in different forms. New parts of the brain could be retrained and rein- tegrated with the rest, and some of that might even happen spontaneously. Progress in regenerative medicine in the past few years is already leading to this form of treatment for neu- rodegenerative conditions like Parkinson’s. LIMITATIONS OF HUMAN WISDOM Even before our bodies wear out, I suspect that we run into limitations of our brains. As a species we seem to have reached a plateau in our intellectual development. There is no sign that we are getting smarter. Was Albert Einstein a better scientist than Newton or Archimedes? Has any playwright in recent years topped Shakespeare or Euripides? We have learned a lot in two thousand years, yet much ancient wisdom still seems sound – which makes me suspect that we haven’t been making much progress. We still do not know how to deal with con- flicts between individual goals and global interests. We are so bad at making important decisions that, whenever we can, we leave to chance what we are unsure about. Why is our wisdom so limited? Is it because we do not have the time to learn very much, or that we lack enough capac- ity? Is it because, as in popular legend, we use only a fraction of our brains? Could better education help? Of course it can, but only to a point. Even our best prodigies learn no more than twice as quickly as the rest. Everything takes us too long to learn because our brains are so terribly slow. It would cer- tainly help to have more time, but longevity is not enough.