Dying makes sense from an evolutionary perspective because it leaves the way clear for the next generation. But why do we get old? Why don’t we just die after we’ve reproduced? Some species of animals and plants – such as salmon, male ants and bamboo – actually do just that. But despite the many advances that age research has made over the past two or three decades, we still cannot fully explain why we humans, along with many other organisms, age.
In general, we can define ageing as a decline in physiological functions over time that occurs in almost all living things. The ageing process is affected by external factors, such as diet, and by internal factors, such as an organism’s genetic make-up. A major breakthrough in age research came when scientists discovered that changes in just one gene were enough to slow the ageing process and significantly increase an organism’s lifespan. The finding was first demonstrated using roundworms, but scientists have now shown that the same genes also play an important role in other creatures and are probably involved in regulating life expectancy in humans.
One of the main causes of ageing is thought to be damage to cells that accumulates over time. The damage can be caused by external influences, such as UV rays, and by processes that happen in the cell itself and produce things like free radicals that then interact with other biomolecules and harm them. Cells have a variety of defence systems that can render harmful substances innocuous. However, these systems become less efficient as we get older and this leads to an increased build-up of damaged biomolecules. The defective molecules progressively restrict normal cell function until, eventually, the cell dies. What’s interesting is that some of the genes that are known to be involved in regulating lifespan also code for proteins that play a part in eliminating harmful substances.
Another possible cause of ageing is the shortening that occurs at the ends of chromosomes, which are the parts of the cell that carry our genetic information. The chromosome ends are protected by things known as telomeres, and every time a cell divides, part of the telomere is lost. When the telomeres get too short, the cell can no longer divide. This can lead to a situation where organ function is restricted because tissues lose some of the ability to repair themselves after an injury or simply due to wear and tear.
In short, ageing is a complex process that depends on many different factors. And even though we have learned a great deal about the molecular mechanisms of aging over the past few years, many fascinating questions remain, and these will be the focus of age research in the coming years. One of the questions asks whether we will one day be able to extend human lifespans in the same way as we can with some creatures today.
This question was answered by Dr Sebastian Grönke of the Max Planck Institute for Biology of Ageing in Cologne.