Theories of aging often look at the behaviors of older adults and how they are influenced by personal choices, societal pressure, and changes to socioeconomic networks. What if the way people think, behave, and act as they age had a biological influence to it? This is essentially what Thomas Kirkwood proposed in 1977 when he published his disposable soma theory of aging.
Kirkwood worked as a statistician at the time he published this initial theory of aging. He has gone on to publish several additional works regarding the science of aging because of his research work at the University of Newcastle. His idea is this: that an organism only has a limited amount of energy and it must be divided between reproduction and non-reproductive aspects of the organism.
Does the Human Body Budget Its Energy?
Kirkwood proposes that a human body is required to budget the amount of energy that is available to it on a daily basis. Every action taken, either voluntarily or not, has an energy expenditure. The disposable soma theory breaks down the budget line for energy distribution into three separate categories: metabolism, reproduction, and repair/maintenance.
This budget must be in place because there is a finite food supply given to the human body each day. It requires a compromise to be made so that each system does not operate at its full potential. Over time, as people age, the energy requirements for each system evolve as well. The compromises made for the three major systems shift. More energy is budgeted for repair and maintenance and the metabolism, which means less energy is available for reproduction.
Although there is individual variability in how these energy transfers occur, the compromises operate in a similar curve for everyone. Over time, less energy is dedicated to reproduction. This means the evolutionary developmental and gestation rates must counter this energy transfer by putting biological pressure on people to have children before a certain time.
If you’ve ever heard of someone talking about their “ticking clock” to have children, that would be a description of Kirkwood’s disposable soma theory.
How Much Energy Goes to Reproduction?
As people age, there are several pressures placed on the reproductive system. This includes the amount of food that people eat. There is a direct correlation to a lower energy level in the reproductive system and lower food intake levels. The other budgeted energy levels are also reduced, but not necessarily to the same extent.
That is why the idea that reproductive energy is the first line-item that is compromised by the body is the foundation of the disposable soma theory. The repair and maintenance requirements of the body are lower with a lower caloric intake, but the energy budget remains proportionally the same. This is also true with the metabolism energy requirement. Digestion may not be necessary, but the body will pull energy from stored fat resources if needed to maintain proper functionality.
For this theory of aging, it explains why people can feel pressures at different times for having children. Based on their diet, lifestyle, and other factors that affect their health, more energy may be dedicated to maintenance and repair or metabolism. Since there is a finite budget of energy available, the body draws from reproductive energies to support the other needs.
Concerns with the Disposable Soma Theory
The idea that processes begin to deteriorate as a person ages is widely accepted. Dead cells are replaced with live cells. Your fingernails continue to grow. Your hair continues to grow and it might even start growing in places you don’t like as you age – like inside your ear canal. Wounds heal. Infections are defeated.
In the disposable soma theory, an assumption must be made for it to work properly. Organisms would be able to reduce repair or maintenance in time, but the adverse effects of that reduction would not occur until later. This creates an energy trade-off that doesn’t account for the fact that some biological needs are short-term, but others are long-term.
Your hair grows a little bit every day. Your brain cells are replaced with much less frequency. This would mean that reducing long-term maintenance resources would create very little energy transfer. It has also been shown through direct observation that some animals and people still have an increased reproductive capacity as older adults, which conflicts with the idea that there is a tradeoff which occurs between aging and reproduction.
The disposable soma theory offers a way to explain aging through a scientific process. Further research and experimentation will be required to determine how accurate it happens to be.