Aging destroys fitness. How could aging have evolved?
Below is my answer to this question. This is mainstream
science from peer-reviewed journals [Ref
but it is my science,
and as Richard Feynman warned us*, I’m the last one who can
be objective about the merits of this theory.
Too fit for its own good
In 1874, a swarm of Rocky Mountain Locusts descended on the
American midwest. They covered the sky and shadowed the
earth underneath for hundreds of miles. A single cloud was
larger than the state of California. Once on the ground,
they ate everything that was green, leaving behind a dust
bowl. The earth was thick with egg masses, ready to renew
the plague the following year.
Huge brown grasshoppers were hitting the ground all
around her, hitting her head and her face and her arms.
They came thudding down like hail. The cloud was hailing
grasshoppers. The cloud was grasshoppers. Their bodies
hid the sun and made darkness. Their thin, large wings
gleamed and glittered. The rasping, whirring of their
wings filled the whole air and they hit the ground and
the house with the noise of a hailstorm. Laura tried to
beat them off. Their claws clung to her skin and her
dress. They looked at her with bulging eyes, turning
their heads this way and that. Mary ran screaming into
the house. Grasshoppers covered the ground, there was
not one bare bit to step on. Laura had to step on
grasshoppers and they smashed squirming and slimy under
The locusts returned in several more seasons, but the last
reported sighting of a Rocky Mountain locust was
in 1902. There are preserved specimens in museums and
laboratories today, but no living locusts. Entomologists
interested in the locust’s rise and fall travel to the
glaciers of Wyoming, mining hundred-year-old ice for
carcasses that they might study.
Where did they go? The Rocky Mountain Locust drove itself
to extinction by overshooting its sustainable population.
Every animal species is part of a food web, and depends on
an ecosystem to survive. If the ecosystem collapse, it takes
down every species and every individual with it. Because of
their mobility, the locusts were able to devastate many
ecosystems, denuding one landscape, then flying hundreds of
miles to deposit their children in a fresh location.
Animals that can’t fly become victims of their own greed
much more quickly than the locust. If the lions killed every
gazelle on the Serengeti, how long would it be before the
lions were gone, too?
Evolution of Individuals and Groups
How would an evolutionary biologist describe this situation?
Were the locusts too fit for their own good? To capture this
story, you have to distinguish between individual fitness
and collective fitness. Individually, these locusts were
super-competitors. Collectively, they were a circular firing
squad. The science of individual fitness and collective
fitness is called Multi-level
Selection Theory, and it has been spearheaded by David
S Wilson of Binghamton University, based on theoretical
foundations by George
Price. MLS is regarded with suspicion by most
evolutionary biologists, but embraced by a minority as sound
Selfish organisms that consume as much of the available food
species as possible may thrive for a time. They may crowd
out other individuals of the same species that compete less
aggressively. But as soon as their kind grows to be the
majority, they are doomed – they wipe out the food source on
which their children depend.
Animals are evolved to be “prudent predators”†. Species
that have exploited their food sources too aggressively, or
that have reproduced too fast have become extinct in a
series of local population crashes. These extinctions have
been a potent force of natural selection, counterbalancing
the better-known selective pressure toward ever faster and
more prolific reproduction.
How did Evolutionary Theory go Wrong?
This is an idea that has common-sense appeal to anyone who
thinks logically and practically about evolutionary science.
In order not to to appreciate this idea, you need years of
training in the mathematical science of evolutionary
genetics. Evolutionary genetics Evolutionary
genetics is an axiomatic framework, built up logically
from postulates that sound reasonable, but the conclusions
to which they lead are deeply at odds with the biological
world we see. This is the “selfish
gene” theory that says all cooperation in nature is a
sort of illusion, based on a gene’s tendency to encourage
behaviors that promote the welfare of other copies of the
same gene in closely-related individuals.
The “selfish gene” is an idea that should have been rejected
long ago, as absurd on its face. Yes, there is plenty of
selfishness and aggression in nature. But nature is also
rich with examples of cooperation between unrelated
individuals, and even cooperation across species lines,
which is called “co-evolution”. Species become intimately
adapted to depend on tiny details of the other’s shape or
habits or chemistry. Examples of this are everywhere, from
the bacteria in your gut to the flowers and the honeybees.
In the same way, predators and their prey (I’m using this
word to include plant as well as animal food sources) adapt
to be able to co-exist for the long haul. It is obvious to
every naturalist that there is a temperance in nature’s
communities, that when ecosystems are out of balance they
don’t last very long.
It makes good scientific sense that extinctions from
overpopulation are a powerful evolutionary force, and it is
part of Darwin’s
legacy as well. Natural selection is more than merely a
race among individuals to reproduce the fastest. The very
word “fitness” came from an ability to fit well into the
life of the local community.
But beginning some forty years after Darwin’s death,
mathematical thinking has led the evolutionary theorists
astray. They have forgotten the first principle of science,
which is that every theory must be validated by comparing
predictions from the theory to the world we see around us.
Predictions of the selfish gene theory work well in the
genetics lab, but as a description of nature, they fail
Understanding Aging based on Multi-level Selection
In we are willing to look past the “selfish gene” and
embrace the science of multi-level selection, we can
understand aging as a tribute paid by the individual in
support of the ecosystem. If it weren’t for aging, the only
way that individuals would die would be by starvation, by
diseases, and by predation. All three of these tend to be
“clumpy” – that is to say that either no one is dying or
everyone is dying at once. Until food species are exhausted,
there is no starvation; but then there is a famine, and
everyone dies at once. If a disease strikes a community in
which everyone is at the peak of their immunological
fitness, then either everyone can fend it off, or else
everyone dies in an epidemic. And without aging, even death
by predation would be very clumpy. Many large predators are
just fast enough to catch the aging, crippled prey
individuals. If this were not so, then either all the prey
would be vulnerable to predators, or none of them would be.
There could be no lasting balance between predators and
Aging helps to level the death rate in good times and bad.
Without aging, horde dynamics would prevail, as deaths would
occur primarily in famines and epidemics. Population would
swing wildly up and down. With aging comes the possibility
of predictable life spans and death rates that don’t
alternately soar and plummet. Ecosystems can have some
stability and some persistence.
Aging is plastic, providing further support for ecosystem
This would be true even if aging operated on a fixed
schedule; but natural selection has created an adaptive
aging clock, which further enhances the stabilizing effect.
When there is a famine and many animals are dying of
starvation, the death rate from old age is down, because of
the Caloric Restriction effect. In times of famine and
other environmental stress, the death rate from aging
actually takes a vacation, because animals become hardier
and age more slowly.
When we ask “Why does an animal live longer when it is
starving?” the answer is, of course, that the ability
to last out a famine and re-seed the population when
food once again becomes plentiful provides a great selective
advantage. This may sound like it is an adaptation for
individual survival, consistent with the selfish gene. But
we might ask the same question conversely: “Why does an
animal have a shorter life span when there is plenty to
eat?” When we look at it this way, it is clear that tying
aging to food cannot be explained in terms of the selfish
gene. In order to be able to live longer under conditions
of starvation, animals must be genetically programmed to
hold some fitness in reserve when they have plenty to eat,
and this an advantage only to the community, not to the
Hormesis is an important clue concerning the
evolutionary meaning of aging. This word refers to the fact
that when an individual is in a challenging environment, its
metabolism doesn’t just compensate to mitigate the damage,
but it overcompensates. It becomes so much stronger that it
lives longer with challenge than without. The best-known
example is thatt people (and animals) live longer when
they’re underfed than when they’re overfed. We also know
that exercise tends to increase our life expectancy, despite
the fact that exercise generates copious free radicals (ROS)
that ought to be pro-aging in their effect.
Without aging, it is difficult for nature to put together a
stable ecosystem. Populations are either rising
exponentially or collapsing to zero. With aging, it becomes
possible to balance birth and death rates, and population
growth and subsequent crashes are tamed sufficiently that
ecosystems may persist. This is the evolutionary meaning of
aging: Aging is a group-selected adaptation for the purpose
of damping the wild swings in death rate to which natural
populations are prone. Aging helps to make possible stable
“ The first principle is that you must not fool yourself,
and you are the easiest person to fool.” – R
P Feynman (from the Galileo Symposium, 1964)
† Here “predator” can mean herbivore as well as carnivore.
This is the common usage in ecology.