Grimm D. Why we outlive our pets. Science 2015 Dec4;350(6265):1182-1185.
Dr. David Grimm, online news editor for Science Magazine, wrote one of the lead articles in Science Magazine, Dec. 4, 2015 issue, which was titled “Why We Age”. Within this issue, topics delve into trying to understand the cellular and molecular mechanisms that drive aging and death.
Perhaps it is a bit odd writing about this article for a feline health science blog, but I just couldn’t put it down and I wanted to share it with the Winn reader community. I was driven to look up publications by researchers that Dr. Grimm interviewed in his article; namely, Drs. Daniel Promislow, Steven Austad, and João Pedro de Magalhães. Boy! Dr. Austad sounds like a brilliant character with an interesting life path from taxi driver, newspaper reporter, lion trainer to distinguished biogerontologist professor at the University of Alabama, Birmingham.
The article starts with the philosopher Aristotle and his observation around 350 B.C. that bigger animals tend to live longer than smaller animals. Although his explanation for the observation being dependent on moisture was off the mark, the size and longevity trend is in general true. Dr. Austad mentions other hypotheses that tried to account for the size-longevity connection; namely, animals with higher metabolic rates live shorter lives because they run out their body clock faster and short-lived animals generate more tissue-damaging free radicals or have cells that stop dividing sooner. These hypotheses, by the way, don’t stand up in general.
Austad’s research with opossums lead to the insight that the reason Aristotle’s key observation continues to hold true is that large animals face fewer dangers (e.g., infectious disease, predation, etc.) Due to evolutionary pressure, they can invest resources leading to robust bodies that will allow them to sire many rounds of offspring. Mice and other heavily preyed-on small animals, on the other hand, live life in fast-forward: They need to put their energy into growing and reproducing quickly, not into developing hardy immune systems.
When it comes to cats and dogs, the bigger-is-better theory doesn’t, at first glance, pan out. Cats live an average of 15 years, compared with about 12 years for dogs, despite generally being smaller. And small dogs can live twice as long as large dogs. However, from Austad’s prospective, gray wolves, the ancestors of dogs, live a maximum of 11 or 12 years in the wild, whereas wildcats can live up 16 years. These two species face different evolutionary pressures. For example, wolves are more social than wild cats and thus more likely to spread infectious disease (i.e., danger). Indeed, two other small animals that are good at avoiding danger, naked mole rats and bats, can live 30 and 40 years, respectively. Meanwhile mice, which are the same size as the naked mole rat, live just a couple of years.
Our cats’ longevity is influenced by unique evolutionary pressure of their ancestry. Clearly tiny and gigantic dog breeds, having only been around for ~ 100-150 years, are not dictated by evolutionary pressure. All of this uniquely positions dogs and cats to possibly help solve the riddle of how we ourselves grow old. Perhaps they hold the clues to slowing down the body clock for all of us—and maybe even stopping it. Who wants to live a 1000 years or forever if our feline companions can’t live right along with us anyways? (GO)
Austad, SN. Cats, “rats”, and bats: the comparative biology of aging in the 21st century. Integr Comp Biol. 2010 Nov;50(5):783-792. (Free PMC article)