Likelihood of death doesn’t always increase with age
Different species of plants and animals age in very different ways. In fact, in some species, the likelihood of death actually decreases the older they get. These findings, made by an international team of researchers, including UvA Professor Hal Caswell, have recently been published in the authoritative scientific journal 'Nature'.
The researchers drew a clear distinction between ageing (the increase in the probability of death as age increases) and lifespan, and concluded that rapid ageing doesn’t always correlate with a short life. A case in point is the Tundra vole, a type of rodent that has a lifespan of about one year. Over the course of that year, the vole's death rate increases by only a factor of 2. Compare this with humans, whose death rate increases by a factor of 20 over the course of their lifespan (of nearly a century).
Absence of ageing
With evolutionary biologists still unable to provide a clear explanation for ageing, this new research demonstrates the incredibly complex diversity in ageing processes. Indeed, the team's findings are at direct odds with prevailing theories on ageing, which assume that mortality increases with age. As it turns out, there are species – such as hydras and hermit crabs – whose death rates remain constant over their entire lifespans. The fact that their physical condition does not deteriorate over the course of their lives, suggests that these species simply do not age. Moreover, there are even species whose probability of death decreases as they get older, like the sea fan, oak and desert tortoise. Of course, this does not mean their likelihood of dying shrinks to zero as they get older; rather, compared to their situation in youth, their chance of reaching their next birthday increases as they age.
New population analysis
As professor of Mathematical Demographics and Ecology at the UvA, Caswell has developed a method for obtaining information from ageing data that, on the face of it, bears no obvious relation to age. Using a complex mathematical process, he analysed all the different possible development paths of species with different life cycles, development patterns and ecological needs and then reconstructed the birth and death rates of each. Such an analysis would have been impossible using the standard approach to demographic problem-solving.
The research was conducted by scientists from the UvA's Institute for Biodiversity and Ecosystem Dynamics (IBED), the Max Planck Institute for Demographic Research (MPIDR) in Rostock (Germany) and the Max Planck Odense Center on the Biodemography of Aging (MaxO) in Odense (Denmark).
Owen R. Jones, Alexander Scheuerlein, Roberto Salguero-Gómez, Carlo Giovanni Camarda, Ralf Schaible, Brenda B. Casper, Johan P. Dahlgren, Johan Ehrlén, María B. García, Eric Menges, Pedro F. Quintana-Ascencio, Hal Caswell, Annette Baudisch, James W. Vaupel: ‘Diversity of Ageing Across the Tree of Life’, in: Nature (2013), DOI: 10.1038/nature12789.