Aging came into being very early in the history of life, resulting from the evolution of strategies to deal with the inevitable accumulation of metabolic waste and damaged molecules in single-celled organisms: operating any sort of machinery produces wear and byproducts, and this is just as true of biological machinery. This can be seen in bacteria today, where cell division can shift most or all of the damage onto one of the daughter cells, using reproduction as a way to dilute waste and damage to maintain a core population that is pristine. The cost is a secondary population that is aging, becoming more damaged over time. These strategies were inherited by multicellular organisms, and show up in, for example, stem cell populations that must maintain themselves for long periods of time. There is a clear spectrum of collective action in mechanisms relevant to aging that reaches from the bacterial collaboration observed in the research here to the highly organized behavior of tissues and their stem cells in our species. At root, it is all about how to deal with damage, and aging is absolutely a matter of damage accumulation.
Microorganisms like bacteria reproduce by growing and dividing into two new bacteria. The older the bacteria, the more defects they have accumulated. When bacteria divide, the two new bacteria look the same, but the question is whether the defects are divided equally between the two new individuals. The researchers performed experiments in the laboratory and made model calculations. They wanted to investigate what was best for the bacterial community. Would it be best to have a colony that was aged to the same degree? Or would it be better for the colony to have the aging defects accumulate in some individuals, while others were free of aging defects and were thus younger?
In the laboratory they studied the bacterial colonies under different conditions and influences. The measurements showed that when a colony was left in peace, the bacteria shared almost symmetrically, so the new individuals were fairly similar with the same number of defects. However, if they exposed the colony to 'stress' in the form of heat or bacteriostatic compounds, cell division was asymmetrical. Now the defects gathered in one bacterium, which then aged and also grew at a slower rate. "What we have found is that the asymmetry of cell division is not controlled genetically. It is a process that is controlled by the physical environment. Through collective behaviour, the bacterial colony that is exposed to stress can stay young, produce more offspring and keep the colony healthier." This is a process that is probably universal and applies to cells in many organisms, including for stem cells. A single individual cell cannot overcome the damage, but the group of cells can do so together. The strength lies in the collective behaviour.