To understand human longevity, we need to put it into perspective. Are we relatively long-lived or short-lived creatures? After all, among all the plants and animals in nature, we find a vast variety of lifespans, from several hours to several millennia, and possibly even more.
While humans are the most long-lived primates, our lifespan pales in comparison to that of many other animals. If we all are created from the same building blocks, why do some animals live fast and die young, others live slow and die old, and some manage to live fast and die old anyway? What can we learn from such organisms that can help us in our quest for longer and healthier human lives?
These are some of the questions that the new book by Steven N. Austad, Methuselah’s Zoo, is trying to answer. Austad is a famed veteran geroscientist with an incredibly interesting personal story that he recounted in his interview with Lifespan.io. In short, in his younger years, Austad dreamed of becoming a novelist, dropped out of college, and worked in a variety of quirky jobs, culminating in training large animals for Hollywood.
This part of his biography includes transporting a live tiger across several states on the back seat of a car and being mauled by an unrelated tiger a few years later. After recovery, Austad decided to study animals in a safer and more meaningful way, got back to school and became a biologist. While he ended up never writing a single novel, Austad’s talent for writing is very much present in the book, making it a captivating read.
Initially, Austad’s interests did not include aging. He studied various animals across the globe, but fluctuations in lifespan between and inside species caught his attention, and he gradually became one of the most prominent experts in animal lifespan. Methuselah’s Zoo is his attempt to tell the incredible story of how various species age – and fight aging.
The wonders of animal longevity
Longevity is relative. One of the most direct and well-established correlations is between lifespan and body size; this is true when comparing species and not individuals of the same species, where the correlation can be positive, negative, or nonexistent. Larger species usually live longer. However, there are outliers, and when hunting for anti-aging strategies developed by evolution, those outliers are the usual suspects.
Some tortoise species can live into their 150s, like the live tanks that crawl the Galapagos islands. They live slowly in a way that humans cannot, but that’s not the only reason for their enviable longevity. Tortoises also deal very well with DNA damage and cancer. Like with most other death-defying tricks described in the book, we simply don’t know how they do it yet.
Then there are flying vertebrates: birds and bats. Many of these species, even at tiny sizes, live for decades, and some birds can outlive a human. This is even more incredible considering how demanding flight is. Birds and bats spend enormous amounts of energy in flight and produce enormous amounts of free radicals, although less than human cells produce under a similar load, but they just seem to be very good at mitigating this type of damage.
Bats have also developed incredible resistance to viruses. Their tightly packed colonies are hotbeds for viruses that sometimes jump over to human populations, but instead of just fighting those viruses, we should also be asking ourselves how bats do it.
While long-lived birds and bats are very active, they actually develop and reproduce slowly, with late puberty, one offspring at a time, and long gaps between births, which is also common in many other long-lived species. Slow reproduction is usually associated with longer lifespan, but again, we don’t know why.
However, ants and termites seem not to fit this pattern. Their queens can live for decades, dozens of times longer than workers, despite having the same DNA and producing an egg a minute for their whole lives. Apparently, queens turn on pro-longevity genes that are turned off in workers.
Yet another quality that seems to unite most long-lived species is the lack of environmental hazards, be it elements or predators. Species ensure their own safety in various ways. Large animals, such as elephants or whales, are simply hard to kill. Others may choose to live underground, like the famous naked mole rat (which is neither a mole nor a rat), the amazing mouse-sized animal that lives for about 40 years.
However, naked mole rats live a long time not just because no predator can get to them. They are also known to boldly defy any carcinogen that scientists have thrown at them (lab mice, quite on the contrary, die mostly of cancer). Long-lived species have also been found in other safe environments, such as caves.
Partnering with evolution
Probably the most amazing takeaway from the book it that there seems to be no type of age-related damage that some species have not developed defenses against. Some have conquered cancer. Others, such as the bivalve mollusk Arctica islandica, which lives at least 500 years, easily deal with mind-boggling amounts of oxidative stress. Birds and bats are much better than humans in countering protein misfolding and extracellular matrix degradation.
Over billions of years, evolution has found numerous niches where longevity could develop and numerous ways to develop it. There is no single formula that every long-lived species follows, but there is an astonishing variety of paths to living longer – and maybe forever, if what we suspect about the immortal jellyfish is true.
Moreover, longevity can develop relatively fast on the evolutionary time scale. For instance, mice are evolutionarily quite close to naked mole rats, despite more than a ten-fold difference in lifespan. The same is true for bivalve mollusks; some species live just over one year, and others live for centuries.
This conclusion is deeply optimistic. The cure for aging is out there, if only we can find the way to combine our own ingenuity with that of nature. While we cannot slow our metabolism like tortoises, grow our telomeres during hibernation like bats, or live in ice-cold water like Arctica islandica, we can potentially elucidate their anti-aging mechanisms and use them to devise therapies for humans.
However, this is a hard task that researchers must commit to. It requires intensive resources to be diverted to studying long-lived species in the wild and in captivity and to expanding our repertoire of lab species. Or, in Austad’s words, “Let’s acknowledge that evolution is cleverer than you are*. Are you listening, Silicon Valley zillionaires?”
Austad finishes on a slightly more serious note: “Until we make a firm commitment to study in depth the animals that can do these things and not remain stuck in our research on the short-lived, rapidly aging species that fill our biomedical labs today, we are unlikely to make much progress in achieving longer, healthier human lives.”
Obviously, we are barely scratching the surface of Austad’s bestiary of long-lived species here. This book contains information about the rougheye rockfish with its 200-year lifespan, the bowhead whale, which is the longest-lived mammal, and other amazing creatures. If you share Austad’s conspicuous love of all living things, along with his passion for fighting aging, you will enjoy the book even more.
We briefly spoke with Steven Austad about his new book.
What is the book’s main idea?
The main idea is that nature, i.e., evolution, is smarter than we are. It has had hundreds of millions of years and billions of species with which to tinker with resistance to the damaging processes of aging and that we would be well-served to take advantage of nature’s successes to improve and extend our own health.
While the book is essentially optimistic, it poses more questions than it provides answers. How would you describe the current situation in animal longevity research?
We now understand a great deal about the basic biology of aging and how to modify the rate of aging in rapidly-aging, short-lived species. What we still need to achieve is to learn how to do the same in slow-aging, long-lived species like ourselves. We are discovering more and more species of what I call “exceptional biogerontological interest,” because they age more successfully than humans. However, studies of these species are sparse. We need to expand our bestiary if we want to discover more and better ways to resist aging.
What have been the most interesting recent developments in studying animal longevity?
The discovery that I think shows the most promise is the impact of young blood/old blood transfusion. It looks right now that toxic substances build up in the blood of older individuals, that if diluted periodically with either young blood or a young blood substitute improves many aspects of health.
Why am I pretty enthusiastic about this? First, it makes sense that as blood circulates through increasingly damaged organs, it would pick up debris from damaged and dying cells and that such debris is likely to itself be damaging (as you can tell, I think the effect is more likely to be about the toxic properties of old blood rather than the rejuvenating properties of young blood). Second, it is something that is easily translatable among species. Comparative analysis of the components of young and old blood in aging-resistant species such as birds and bats compared with aging-prone species has a great deal to teach us about healthy longevity.
* “Evolution is cleverer than you are” is a saying by the biochemist Leslie Orgel, known as “Orgel’s second rule”, which Austad acknowledges.