Something has always bugged me about the Paleo diet. Well, I guess the first thing is that it's a fad. The next part of it that bugged me was the whole notion that we should do anything like our ancestors. I mean, they caught a bad cold - or even a cold that is a sort of 24 hour sniffles to modern day us and they were as good as dead.
That's the luxury of, you know, modern technology. We don't need to go out and hunt for our food. But it does bug me some when you hear a paleo dieter go on about how they're eating all Paleo and they order something like eggs with avocado and salmon along with some protein enriched milk smoothie. Like, how lucky for that cavemen to live so close to both a fish source, avocado trees, cows and chickens. Yeah, I don't think that's very realistic.
Our maladapted ancestors
The
paleofantasy is a fantasy in part because it supposes that we humans, or
at least our protohuman forebears, were at some point perfectly adapted
to our environments. We apply this erroneous idea of evolution
producing the ideal mesh between organism and surroundings to other
life-forms too, not just to people. We seem to have a vague idea that
long long ago, when organisms were emerging from the primordial slime,
they were rough-hewn approximations of their eventual shape, like toys
hastily carved from wood, or an artist’s first rendition of a portrait,
with holes where the eyes and mouth eventually will be. Then, the
thinking goes, the animals were subject to the forces of nature. Those
in the desert got better at resisting the sun, while those in the cold
evolved fur or blubber or the ability to use fire. Once those traits had
appeared and spread in the population, we had not a kind of sketch, but
a fully realized organism, a fait accompli, with all of the lovely
details executed, the anatomical t’s crossed and i’s dotted.
But of
course that isn’t true. Although we can admire a stick insect that seems
to flawlessly imitate a leafy twig in every detail, down to the marks
of faux bird droppings on its wings, or a sled dog with legs that can
withstand subzero temperatures because of the exquisite heat exchange
between its blood vessels, both are full of compromises, jury-rigged
like all other organisms. The insect has to resist disease, as well as
blend into its background; the dog must run and find food, as well as
stay warm. The pigment used to form those dark specks on the insect is
also useful in the insect immune system, and using it in one place means
it can’t be used in another. For the dog, having long legs for running
can make it harder to keep the cold at bay, since more heat is lost from
narrow limbs than from wider ones. These often conflicting needs mean
automatic trade-offs in every system, so that each may be good enough
but is rarely if ever perfect. Neither we nor any other species have
ever been a seamless match with the environment. Instead, our adaptation
is more like a broken zipper, with some teeth that align and others
that gape apart. Except that it looks broken only to our unrealistically
perfectionist eyes—eyes that themselves contain oddly looped vessels as
a holdover from their past.
Even
without these compromises from natural selection acting on our current
selves, we have trade-offs and “good enough” solutions that linger from
our evolutionary history. Humans are built on a vertebrate plan that
carries with it oddities that make sense if you are a fish, but not a
terrestrial biped. The paleontologist Neal Shubin points out that our
inner fish constrains the human body’s performance and health because
adaptations that arose in one environment bedevil us in another.
Hiccups, hernias, and hemorrhoids are all caused by an imperfect
transfer of anatomical technology from our fish ancestors. These
problems haven’t disappeared for a number of reasons: just by chance, no
genetic variants have been born that lacked the detrimental traits, or,
more likely, altering one’s esophagus to prevent hiccups would entail
unacceptable changes in another part of the anatomy. If something works
well enough for the moment, at least long enough for its bearer to
reproduce, that’s enough for evolution.
We can
acknowledge that evolution is continuous, but still it seems hard to
comprehend that this means each generation can differ infinitesimally
from the one before, without a cosmic moment when a frog or a monkey
looked down at itself, pronounced itself satisfied, and said, “Voilà, I
am done.” Our bodies therefore reflect a continuously jury-rigged system
with echoes of fish, of fruit fly, of lizard and mouse. Wanting to be
more like our ancestors just means wanting more of the same set of
compromises.
When was that utopia again?
Recognizing
the continuity of evolution also makes clear the futility of selecting
any particular time period for human harmony. Why would we be any more
likely to feel out of sync than those who came before us? Did we really
spend hundreds of thousands of years in stasis, perfectly adapted to our
environments? When during the past did we attain this adaptation, and
how did we know when to stop?
If they had
known about evolution, would our cave-dwelling forebears have felt
nostalgia for the days before they were bipedal, when life was good and
the trees were a comfort zone? Scavenging prey from more formidable
predators, similar to what modern hyenas do, is thought to have
preceded, or at least accompanied, actual hunting in human history.
Were, then, those early hunter-gatherers convinced that swiping a
gazelle from the lion that caught it was superior to that newfangled
business of running it down yourself? And why stop there? Why not long
to be aquatic, since life arose in the sea? In some ways, our lungs are
still ill suited to breathing air. For that matter, it might be nice to
be unicellular: after all, cancer arises because our differentiated
tissues run amok. Single cells don’t get cancer.
Even
assuming we could agree on a time to hark back to, there is the sticky
issue of exactly what such an ancestral nirvana was like. Do we follow
the example of the modern hunter-gatherers living a subsistence
existence in a few remaining parts of the world? What about the great
apes, the animals that most closely resemble the ancestors we (and they)
split off from millions of years ago? How much can we deduce from
fossils? People were what anthropologists call “anatomically modern,”
meaning that they looked more or less like us, by about 200,000 years
ago, but it’s far less clear when “behaviorally modern” humans arose,
or what exactly they did. So, trying to deduce the classic lifestyle
from which we’ve now deviated is itself a bit of a gamble. In his book
Before the Dawn, science writer Nicholas Wade points out, “It is
tempting to suppose that our ancestors were just like us except where
there is evidence to the contrary. This is a hazardous assumption.”
You might
argue that hunter-gatherers, or the cavemen of our paleofantasies, were
better adapted to their environment simply because they spent many
thousands of years in it—much longer than we’ve spent sitting in front
of a computer or eating Mars bars. That’s true for some attributes, but
not all. Continued selection in a stable environment, as might occur in
the deep sea, can indeed cause ever more finely honed adaptations, as
the same kinds of less successful individuals are weeded out of the
population. But such rock-solid stability is rare in the world; the
Pleistocene varied considerably in its climate over the course of
thousands of years, and when people move around, even small shifts in
the habitat in which they live, going from warm to cool, from savanna to
forest, can pose substantially new evolutionary challenges. Even in
perfectly stable environments, trade-offs persist; you can’t give birth
to large-brained infants and also walk on two legs trouble-free, no
matter how long you try.
Incidentally,
it’s important to dispel the myth that modern humans are operating in a
completely new environment because we only recently began to live as
long as we do now, whereas our ancestors, or the average
hunter-gatherer, lived only until thirty or forty, and hence never had
to experience age-related diseases. While it is absolutely true that the
average life span of a human being has increased enormously over just
the last few centuries, this does not mean that thousands of years ago
people were hale and hearty until thirty-five and then suddenly dropped
dead.
An average
life expectancy is just that—an average of all the ages that the people
in the population attain before they die. A life expectancy of less than
forty can occur without a single individual dying at or even near that
age if, for example, childhood mortality from diseases such as measles
or malaria is high—a common pattern in developing countries. Suppose you
have a village of 100 people. If half of them die at age five, perhaps
from such childhood ailments, twenty die at age sixty, and the remaining
thirty die at seventy-five, the average life span in the society is
thirty-seven, but not a single person actually reached the age of thirty
hale and hearty and then suddenly began to senesce. The same pattern
writ large is what makes the life expectancy in developing countries so
shockingly low. It isn’t that people in sub-Saharan Africa or ancient
Rome never experienced old age; it’s that few of them survived their
childhood diseases. Average life expectancy is not the same thing as the
age at which most people die. Old age is not a recent invention, but
its commonness is.
The pace of change
If we do
not look to a mythical past utopia for clues to a way forward, what
next? The answer is that we start asking different questions. Instead of
bemoaning our unsuitability to modern life, we can wonder why some
traits evolve quickly and some slowly. How do we know what we do about
the rate at which evolution occurs? If lactose tolerance can become
established in a population over just a handful of generations, what
about an ability to digest and thrive on refined grains, the bugaboo of
the paleo diet? Breakthroughs in genomics (the study of the entire set
of genes in an organism) and other genetic technologies now allow us to
determine how quickly individual genes and gene blocks have been altered
in response to natural selection. Evidence is mounting that numerous
human genes have changed over just the last few thousand years—a blink
of an eye, evolutionarily speaking—while others are the same as they
have been for millions of years, relatively unchanged from the form we
share with ancestors as distant as worms and yeast. The pages to come
will explore which genes and traits have changed, which have not, how we
know, and why it matters.
What’s
more, a new field called experimental evolution is showing us that
sometimes evolution occurs before our eyes, with rapid adaptations
happening in 100, 50, or even a dozen or fewer generations. Depending on
the life span of the organism, that could mean less than a year, or
perhaps a quarter century. It is most easily demonstrated in the
laboratory, but increasingly, now that we know what to look for, we are
seeing it in the wild. And although humans are evolving all the time, it
is often easier to see the process in other kinds of organisms. Humans
are not the only species whose environment has changed dramatically over
the last few hundred years, or even the last few decades. Some of the
work my students and I have been doing on crickets found in the Hawaiian
Islands and in the rest of the Pacific shows that a completely new
trait, a wing mutation that renders males silent, spread in just five
years, fewer than twenty generations. It is the equivalent of humans
becoming involuntarily mute during the time between the publication of
the Gutenberg Bible and On the Origin of Species. This and similar
research on animals is shedding light on which traits are likely to
evolve quickly and under what circumstances, because we can test our
ideas in real time under controlled conditions.
Over the
last decade, our understanding of such rapid evolution, also called
“evolution in ecological timescales,” has increased enormously. And
studying the rate of evolution also has practical implications. For
example, fishermen often take the largest specimens of salmon or trout
from streams and rivers. Fish usually need to reach a certain size
before becoming sexually mature and capable of reproduction, after which
growth slows down. Like other animals, fish show a trade-off between
large size and time of reproduction: if you wait to be large before
producing offspring, you probably will be able to produce more of them,
and having greater numbers of offspring is favored by evolution, but you
also risk dying before you are able to reproduce at all. But where
overfishing has removed a substantial portion of a population, the
average size of fish is now substantially smaller, because the fishermen
have inadvertently selected for earlier reproduction, and evolution has
favored fish that get to the business of sex sooner. It’s not just that
the larger fish have all been taken; it’s that the fish are not
reaching such sizes to begin with. The genes responsible for regulating
growth and size at sexual maturity are now different because evolution
has occurred. To bring back the jaw-dropping trophy fish of decades
past, scientists say, people will have to change their ways.
It’s common
for people talk about how we were “meant” to be, in areas ranging from
diet to exercise to sex and family. Yet these notions are often flawed,
making us unnecessarily wary of new foods and, in the long run, new
ideas. I would not dream of denying the evolutionary heritage present in
our bodies—and our minds. And it is clear that a life of sloth with a
diet of junk food isn’t doing us any favors. But to assume that we
evolved until we reached a particular point and now are unlikely to
change for the rest of history, or to view ourselves as relics hampered
by a self-inflicted mismatch between our environment and our genes, is
to miss out on some of the most exciting new developments in
evolutionary biology.
So I guess I'm going to go enjoy some of our modern day non-paleo inventions. It just goes to show you that the paloe diet isn't the best thing to happen since sliced bread.
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