The Ageing Process
Many of us grew up with the idea that ageing is a biological programme shaped by natural selection to ensure turnover of the generations. Most gerontologists now think this is wrong.
In the wild, old animals are lost to accidents or predators, disease or cold, dying long before they show any signs of damage from ageing. So, ageing as a means of culling the old makes little sense; yet genes certainly exert a powerful influence over the length of life, hence the tendency for longevity to run in families. What are these genes that regulate length of life, if not evolved to direct our death?
Because wild animals die young, natural selection is relatively powerless to eliminate mutations that have their adverse effects in later life, especially if they have a positive impact in a youngster. For example, a high testosterone level may aid the reproductive drive of a young male, but it predisposes to later health problems. For natural selection, early advantage counts much more than trouble which might follow later. This is important when we consider the impact of natural selection on our body’s mechanisms for maintenance and repair.
Maintenance is essential if the body is to retain its health functions. But, maintenance is metabolically expensive and it may be too costly to build a body that could last forever. The ‘disposable soma’ theory suggests that our genes, under pressure from natural selection, settled on a solution ‘good enough’ to see us through the 30 years of ‘nasty brutish and short’ life available to our distant ancestors.
This arrangement is less suited to today’s safer living conditions, so we now age and die because of the limitations of our maintenance and repair. Ageing appears to be a lifelong accumulation of faults at the cellular and molecular level, each a random occurrence insignificant in itself, combining to overwhelm the body’s ability to keep its systems running. The random nature of these faults is what makes us each age so individually, and it is this individuality and the underlying complexity, which makes the ageing process such an intriguing scientific challenge.
Tom Kirkwood – Director IAH
