Fancy, high-quality products such as Rolex watches and Red Wing boots often cost more to make but last longer. This is a principle that manufacturers and customers are familiar with. But while this also applies to biology, scientists rarely discuss it.
Researchers have known for decades that the faster an animal grows, the shorter its lifespan, at least among mammals. This holds across species of different sizes. Ecophysiologists like me have been studying the trade-offs between allocating energy for growth or for maintenance, and how those trade-offs affect aging and lifespan.
One explanation is that since animals have a limited amount of energy available, investing more energy in growth will reduce the energy they have left to maintain their health, therefore leading to faster aging.
Another explanation is based on the observation that metabolism – all the physical and chemical processes that convert or use energy – fuels growth. Some researchers have suggested that fast growth is associated with high metabolism, in turn causing stress that speeds up aging.
However, these two explanations may not capture the whole picture of the trade-off between growth and longevity. For example, certain species allocate a larger fraction of their energy to maintenance but don’t have better resistance to stress than species that allocate less energy to those processes. This finding indicates that the amount of energy allocated to maintenance may not be the only thing that determines its quality.
Meanwhile, I found that this negative association still strongly holds even after accounting for metabolic rate. That means the higher metabolism associated with faster growth cannot completely explain faster aging. There had to be other missing links to consider.
What have scientists overlooked? My recently published research suggests that the energy cost it takes to make biological materials, or the biosynthetic cost, also affects lifespan.
Whales have some of the longest lifespans among mammals.
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Cost of making biomass
It costs energy to make biological materials, or biomass, such as assembling individual amino acids into whole proteins. It also costs energy to check newly synthesized materials for errors, break down and rebuild materials with errors, and transport finished materials to where they need to be.
To measure the energy investment in building biomass across species, I derived a mathematical relationship between biosynthetic cost and rates of growth and metabolism. I based my equation on the first principle of energy conservation, which states that energy is neither created nor destroyed, and data on the growth and metabolism rates of different mammals routinely measured by other researchers in the field.
While researchers previously believed that the cost of synthesizing new biomass was the same across species, my analysis of data from 139…
