Question: what causes humans to grow old

Rebecca Dewey answered on 23 Jun 2015:

We’re not entirely sure. There are theories that people have come up with, and some of them even sound plausible, but we don’t know which one (or combination of more than one) is true.

It is beneficial with evolution for each member of a species to die so that new attempts / improvements can exist. This might be controlled within the programming of the cells in the body, or be caused by external factors outside the body. After a member of the species has reproduced (had children and brought them up to be independent) then they are no longer necessary to the continuation and survival of the species, so biology chooses not to keep them around.

Each time our cells make new cells, the DNA has a chance of getting damaged, either by losing individual genes or sections of DNA or splits and breaks in the DNA. Once the damage in the cells has built up to a certain level, it is not good to carry on making more cells that way, and it is better to start off again from scratch with a new human. This can also apply to the idea of cell repair – once cells have been damaged through wear-and-tear and then repaired a certain number of times, the cell has been compromised and it’s better to start with new.