What is ageing and why do we get older? How It Works looks at the science of senescence and the technologies tackling the inevitable

Words by Scott Dutfield

Ageing is a fact of life we can’t escape no matter how hard we try, though as a species we’re getting better at prolonging the process. For the first time in human history, the global average life expectancy is above 70 years old. In comparison, back in 1950 the global average was only 45 years old. We can predominantly thank the advancement of medicine for letting us live longer, but at what point do we stop growing and start ageing?

It’s generally understood that once we surpass sexual maturity in our late 20s we make the transition from developing into ageing, also referred to as senescence, which means ‘the process of growing old’. After sexual maturity, our bodies become less efficient at dealing with physical stress and maintaining biological systems. That seems to be because of the way our species has evolved.

It might make more sense that, like any machine, if you keep your body well-fuelled and maintained, you could live indefinitely. Generally speaking, many evolutionary biologists have concluded that we age simply because the driving force of evolution, known as natural selection, hasn’t selected for fitness and function at an older age.

Of course, humans aren’t alone in this. The majority of other species have evolved a similar reproductive life cycle – but not all of them. Many cold-blooded species such as lizards retain their fitness and reproductive abilities and are considered to have negligible senescence. These animals age very slowly and typically die from non-age related events such as predation, disease or natural disasters.