I thought that the article on why we age was very interesting. Kirkwood and Austad talk about three theories that provide explanations of why aging occurs. The theory that I found most interesting was how senescence is programmed to limit population size and allow the adaptation of organisms in changing environments. This seems to be true mainly for humans. One large flaw is the fact that wild animals don’t live long enough to grow old. It is hard to say that someone died of old age. Once you get older you are more susceptible to disease. Another theory was that of ‘pleiotropy’. This stated that pleiotropic genes that had good early affects would be favored even if they had poor affects later on. This is an important life-history trade-off, which is something we talk a lot about in this class. This is also a big part of the third theory, the ‘disposable soma’ theory. These two theories are very similar. The pleiotropy theory is based on a general pattern of gene action, while the other focuses specifically on mechanisms. Why we age is interesting but so is how we age. Our life expectancy has gone from around 47 in 1900 to around 80 in 2013. That is a drastic difference. Reading this article has made me want to do more research on why and how we age.