As advances in medicine, hygiene, and safety extend average lives on Earth, it's natural to wonder if some of us belong to the “last mortal generation”, with younger counterparts never needing to grow old or die. An assessment of what we know about aging in Nature Communications, however, argues we are a long way from this. Just like in the fairy stories, death will get all of us in the end, barring something well beyond anything science has yet achieved.
“'Tis impossible to be sure of anything but Death and Taxes,” has been a popular quote for three centuries. However, now that the very rich regard taxes as optional, some have wondered if death too could be beaten, given enough money.
Against this lies what is known as the “invariant rate of aging hypothesis”, which the paper says; “Posits that the rate of aging is relatively fixed within species.” Researchers from 42 institutions in 14 countries combined to explore the idea.
"We were able to shed light on the invariant rate of aging hypothesis by combining an unrepresented wealth of data and comparing births and deaths patterns on nine human populations with information from 30 non-human primate populations, including gorillas, chimpanzees and baboons living in the wild and in zoos," said Dr Fernando Colchero of the University of Southern Denmark in a statement.
Before vaccines and clean water supplies, almost half the population of children died before adulthood, but most of the rest made it to 50. Most of the initial extension of global life expectancy since the mid-1800s came from cutting infant mortality. More recently reducing the death rate among people in their 60s and 70s has also contributed, but there has been less change among the very old, leading to estimates of a maximum human lifespan of 115.
This pattern has been widely noticed, leading to speculation we may now be facing a law of diminishing returns.
Not everyone is convinced, however, seeing this as drawing conclusions from too limited a sample. So Colchero and co-authors expanded to our closest relatives. "We observe that not only humans, but also other primate species exposed to different environments, succeed in living longer by reducing infant and juvenile mortality. However, this relationship only holds if we reduce early mortality, and not by reducing the rate of aging" Colchero said.
Indeed, the paper reports differences in the rate of aging are small within a genus; “Implying biological constraints on how much the human rate of aging can be slowed”. Co-author Dr Jose Aburto of the University of Oxford said; "A steep rise in death rates, as years advance into old age, is clear to see in all species."
If Neanderthals or Homo erectus were still around, and had access to modern medicine, they'd probably have similar life expectancies to our own.
Nor is the rate of aging random, it correlates strongly with things like body size and growth rate, as well as the age of first reproduction. Giant tortoises and Greenland sharks prove you can evolve immense lifespans, but it is neither quick nor easy.
“Not all is lost" Colchero said, “Medical science has advanced at an unprecedented pace, so maybe science might succeed in achieving what evolution could not: to reduce the rate of aging.” However, if it was nearly here, we'd probably see it reflected in demographic patterns, and so far we don't.