The Science of Aging

While many search for the proverbial fountain of youth, you might be wondering why do we age in the first place? What is it about our bodies or cells biologically that causes us to grow old? There is a variety of internal and external factors such as diet, exercise or environmental stress which all contribute to cell damage and repair and effect the rate of aging, But the surprising truth is that apart from these, we actually have a biological clock buried within our genetic makeup. And this clock can only run for so long, in other words we are programmed to die. Your body is made up of trillions of cells which are constantly going through cell division and every time they divide they make a copy of their DNA as well. This DNA is tightly packed into structures called chromosomes of which humans have twenty three pairs. The problem is, DNA replication isn't quite perfect and skips over the end of each chromosome. To protect against important DNA information being cut out we have something called telomeres on the end of chromosomes which are essentially meaningless repeats of DNA that we can afford to lose. But everytime our cells divide these telomeres become shorter and shorter until eventually they've been entirely stripped away. At which point the cell no longer divides. Some flat worms are able to endlessly regenerate their telomeres making them effectively biologically immortal, but their lifespans do vary and they're still susceptible to disease further suggesting that aging is a mix of genetic and environmental factors. But why don't our cells do this? Ultimately this replication limit actually helps to prevent cancer which is the uncontrollable growth of cells and evasion of cell death. The point at which a cell stops replicating is known as cellular senescence. In humans this replication limit is around fifty times. Once it is reached the cell gradually begins to lose its function and die causing age-related characteristics. This also helps to explain why life expectancy is a strongly heritable trait from your parents, because you got your initial telomere length from them. Got a burning question you want answered? Ask it in the comments, or on facebook and twitter, and subscribe for more weekly science videos.