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 		 [ Human evolution is ongoing and our diets still shape our
evolutionary path. Our food choices today will influence the direction
we will take tomorrow.] [https://portside.org/] 




 Brian Handwerk 
 March 31, 2018
Smithsonian Magazine

	* [https://portside.org/node/16888/printable/print]

 _ Human evolution is ongoing and our diets still shape our
evolutionary path. Our food choices today will influence the direction
we will take tomorrow. _ 

 Human evolution is ongoing, and what we eat is a crucial part of the
puzzle, photosil / Alamy 


You aren’t what you eat, exactly. But over many generations, what we
eat does shape our evolutionary path. “Diet,” says anthropologist
John Hawks, of the University of Wisconsin-Madison, “has been a
fundamental story throughout our evolutionary history. Over the last
million years there have been changes in human anatomy, teeth and the
skull, that we think are probably related to changes in diet.”

 As our evolution continues, the crucial role of diet hasn’t gone
away. Genetic studies show that humans are still evolving, with
evidence of natural selection pressures on genes impacting everything
from Alzheimer’s disease to skin color to menstruation age. And what
we eat today will influence the direction we will take tomorrow.

 Got Milk?

 When mammals are young, they produce an enzyme called lactase to
help digest the sugary lactose found in their mothers’ milk. But
once most mammals come of age, milk disappears from the menu. That
means enzymes to digest it are no longer needed, so adult mammals
typically stop producing them.

 Thanks to recent evolution, however, some humans defy this trend.

 Around two-thirds of adult humans are lactose intolerant or have
reduced lactose tolerance after infancy. But tolerance varies
dramatically depending on geography. Among some East Asian
communities, intolerance can reach 90 percent; people of West African,
Arab, Greek, Jewish and Italian descent are also especially prone to
lactose intolerance.

 Northern Europeans, on the other hand, seem to love their
lactose—95 percent of them are tolerant, meaning they continue to
produce lactase as adults. And those numbers are increasing. “In at
least different five cases, populations have tweaked the gene
responsible for digesting that sugar so that it remains active in
adults,” Hawks says, noting it is most common among peoples in
Europe, the Middle East and East Africa. 

Ancient DNA shows how recent this adult lactose tolerance is, in
evolutionary terms. Twenty-thousand years ago, it was non-existent.
Today, about one-third of all adults have tolerance.

That lightning-fast evolutionary change suggests that direct milk
consumption must have provided a serious survival advantage over
peoples who had to ferment dairy into yogurt or cheese. During
fermentation, bacteria break down milk sugars including lactase,
turning them into acids and easing digestion for those with lactose
intolerance. Gone with those sugars, however, is a good chunk of the
food’s caloric content.

Hawks explains why being able to digest milk would have been such a
boon in the past: “You’re in a nutrition limited environment,
except you have cattle, or sheep, or goats, or camels, and that gives
you access to a high energy food that infants can digest but adults
can’t,” he says. “What it does is allow people to get 30 percent
more calories out of milk, and you don’t have the digestive issues
that come from milk consumption.”

A recent genetic study found that adult lactose tolerance was less
common in Roman Britain than today, meaning its evolution has
continued throughout Europe’s recorded history.

 These days, many humans have access to plentiful alternative foods
as well as lactose-free milk or lactase pills that help them digest
regular dairy. In other words, we can circumvent some impacts of
natural selection. That means traits like lactose tolerance might not
have the same direct impacts on survival or reproduction that they
once did—at least in some parts of the world.

“As far as we know, it makes no difference to your survival and
reproduction in Sweden if you can digest milk or not. If you’re
eating out of a supermarket (your dairy tolerance doesn’t affect
your survival). But it still makes a difference in East Africa,”
Hawks says. 

Wheat, Starch and Alcohol

These days, it isn’t uncommon to find an entire grocery store aisle
devoted to gluten-free cookies, bread and crackers. Yet trouble
digesting gluten—the main protein found in wheat—is another
relatively recent snag in human evolution. Humans didn’t start
storing and eating grains regularly until around 20,000 years ago, and
wheat domestication didn’t begin in earnest until about 10,000 years

 Since wheat and rye became a staple of human diets, however, we’ve
have had a relatively high frequency of celiac disease. “You look at
this and say how did it happen?” asks Hawks. “That’s something
that natural selection shouldn’t have done.”

 The answer lies in our immune response. A system of genes known as
the human leukocyte antigens take part in the fight against disease,
and frequently produce new variations to battle ever-changing
infections. Unfortunately, for individuals with celiac disease, this
system mistakes the human digestive system for a disease and attacks
the lining of the gut.

 Yet despite the obvious drawbacks of celiac disease, ongoing
evolution doesn’t seem to be making it less frequent. The genetic
variants behind celiac disease seem to be just as common now as
they’ve been since humans began eating wheat.

 “This is a case where a selection that is probably about disease
and parasites has a side effect that produces celiac disease in a
small fraction of people. That’s a trade-off that recent evolution
has left us and it wasn’t an adaptation to diet—it was an
adaptation in spite of diet,” Hawks says. Unintended trade-offs are
common in evolution. For example, the genetic mutation to red blood
cells that helps humans survive malaria can also produce the deadly
sickle cell disease.

 Other examples of our continuing evolution through diet are
intriguing but uncertain. For instance, Amylase is an enzyme that
helps saliva digest starch. Historically, agricultural peoples from
West Eurasia and Mesoamerica have more copies of the associated gene.
Were they selected to digest starches better? “That makes a
compelling story and it may be true. But biology is complicated and
it’s not totally clear what’s at work or how important it is,”
Hawks says.

 More than one-third of East Asians—Japanese, Chinese and
Koreans—have a flushing reaction when they metabolize alcohol,
because the process creates an excess of toxic acetaldehyde enzymes.
There’s strong genetic evidence that this was selected recently,
during the last 20,000 years, Hawks notes.

 Because its appearance in the genome may roughly coincide with rice
domestication 10,000 years ago, some researchers suggest that it
stopped people from over indulging in rice wine. The timelines
aren’t precisely determined, however, for either the mutation or
rice domestication. It has also been suggested that acetaldehyde
offered protection from parasites that were unable to stomach the

 “It mattered in some way, to past populations, because it wasn’t
common and now it is,” says Hawks. “It’s a big change, but we
really don’t know why.”

 More Important Than We Think?

Even the color of human skin may be shifting, at least in part, as a
response to diet (other factors, studies suggest, include sexual
selection). The current diversity of human skin colors is a relatively
recent development. The standard hypothesis focuses on the prevalence
of UV rays at equatorial latitudes. Our bodies need vitamin D, so our
skin produces it when soaked by UV rays. But too much UV can have
detrimental effects, and darker skin pigments are more effective at
blocking them.

 As humans moved into darker, colder latitudes, the idea goes, their
skin no longer needed protection from too much UV and lightened so
that it could produce more beneficial vitamin D with less sunlight.

 But DNA studies comparing modern Ukrainians with their prehistoric
ancestors show that European skin color has been changing over the
past 5,000 years. To explain this, another theory suggests that skin
pigmentation could have been under the influence of diet, when early
farmers suffered from a lack of vitamin D their hunter-gatherer
ancestors once got from fish and animal foods.

 Nina Jablonski, a skin color researcher at Penn State University,
told Science that new research “provides evidence that loss of
regular dietary vitamin D as a result of the transition to a more
strongly agricultural lifestyle may have triggered” the evolution of
lighter skin.

 It’s difficult to see evolution in action. But new technologies
like genome sequencing—and the computing power to crunch massive
piles of data—are making it possible to spot tiny genetic tweaks
that can add up over many generations to real evolutionary shifts.
Increasingly, databases of genetic information are also paired with
information like medical histories and environmental factors like
diet, which may allow scientists to observe the ways they interact.

 Hakhamanesh Mostafavi, an evolutionary biologist at Columbia
University, authored one such genome study that analyzed DNA from
215,000 people to try to see how we continue to evolve over the span
of just a generation or two. “Obviously our diet is radically
changing today, so who knows what evolutionary effect that may
have,” Mostafavi says. “It may not necessarily have a direct
selection effect but it may interact with genes that control a

 Mostafavi’s genetic research also revealed that some variants that
actually shorten human life, like one that prompts smokers to increase
their consumption above smoking norms, are still being actively
selected against.

 “We see a direct effect of that gene on the survival of humans
today,” he explains. “And potentially you can imagine that diet
might have the same kind of effect. We have so many recent dietary
changes, like fast food for one example, and we just don’t know yet
what effects they may or may not have.”

 Fortunately, thanks to the work of scientists like Mostafavi and
Hawks, it might not take 20,000 years to find out.

Read more:

	* [https://portside.org/node/16888/printable/print]







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