February’s issue of Technology Review (MIT’s alumni magazine) has a provocative article on Aubrey de Grey and his pursuit of immortality. De Grey, who’s day job is computer support for a genetics lab in Cambridge, proposes an ambitious research agenda to extend life. His ideas are actually not that outlandish. He identifies seven weak points in human physiology such as cell degeneration, mutations, and accumulation of “junk” that lead to our eventual demise. His proposal is that bio-engineering methods could be developed to repair these problems.
It may or may not be possible to live forever but I think there is an entirely different issue that he doesn’t address and that is the capacity of our brains is finite. Thus, no matter how long our bodies may live, our memories of it are limited. A Hopfield neural network of associative memory for example has a maximum capacity of about 10% of the number of neurons in the network. After that, memories will begin to overwrite each other. We do have 10^12 neurons or so but that is still a finite number. So an immortal person (without infinite memory capacity) at some point will either overwrite earlier memories or not remember anything new and be frozen in time (like the character in the film Memento).
Any form of memory augmentation could extend the problem but never completely cure it. Thus an immortal person could never have a sense of self that extended over their entire lifetime. They would only remember bits and pieces of it. A second problem is that they would need to adapt and evolve to changing environments. In any case, they would be forced to morph into different beings throughout their lives.
Nature already has a form of immortality and it is called reproduction. It was designed specifically to deal with these issues. De Bray claims that if people had to choose between living forever or having children they would all opt for the former. I personally would not. To me it makes much more sense to try to maximize the chances of survival for our species (or perhaps all forms of life) rather than myself. I would much rather spend our resources trying to make the short lives we have better than spend it on Ponce de Leon’s pipe dream. By just eliminating malaria, tuberculosis and AIDS alone we could significantly improve and extend the lives of many.