3 Diseases We May Be Able to Blame on Our Ancient Ancestors
Obesity, lactose intolerance, and high blood pressure may all be traceable to huntergatherer survival.
November 27th, .2008
by Emily Anthes
The ADHD children of the world may have their wandering ancestors to blame. A genetic variant associated with
impulsivity, novelty seeking, and attention deficit hyperactivity disorder (ADHD) might have actually been adaptive in
nomadic populations, according to a recent study by Dan Eisenberg at Northwestern University. Kenyan nomads with
this variant, he says, may have been better at searching for food and defending their resources, giving them a
survival advantage. But the study shows that the nomads’ settled descendants who carried this gene were more often
malnourished than those without the gene. “Just because we don’t see a trait as being currently advantageous,”
Eisenberg says, “does not preclude the trait from having had a function in the past.” Geneticists continue to unravel
our ancestral evolution in hopes of better understanding how formerly advantageous genes have led to modern-day
health problems.
High Blood Pressure
High blood pressure may be caused by a gene that was key to nomadic survival. The ability to retain salt—controlled
in part by a gene called CYP3A5—varies by latitude, according to geneticists at the University of Chicago. The closer
a population lives to the equator, the better individuals are at retaining salt. “Since hunter-gatherers weren’t assured
of getting sodium every day, they needed to be sure not to lose what they did acquire,” says Alan Weder, a
hypertension specialist. But bring this gene to a modern setting—with couch lounging and salty snacking—and it is
easy to retain more salt than is needed, which can lead to medical problems like high blood pressure.
Lactose Intolerance
Whether or not you can drink milk may depend on where your nomadic ancestors settled down. Early humans, like
other mammals, were able to digest milk only during infancy. But when humans started raising cows and milk
became widely available, an ability to digest it brought a selective advantage, according to genetic research by
Cornell University biologist Paul Sherman. DNA analysis of skeletons from between 5840 and 5000 B.C. found
evidence that the early wave of European farmers could not produce the enzyme lactase, which permits the digestion
of milk, while later farmers could. In regions where dairy farming is currently not safe or economical because of an
extreme climate or cattle diseases, Sherman says, populations still possess ancestral genes that make them lactose
intolerant.
Obesity
Could our growing waistlines be blamed on nomadic ancestors? Some scientists think so. The Pima Indians of
Arizona are a recently settled group whose members today have sky-high rates of obesity and diabetes, thanks to
their genes, say Leslie Baier and her colleagues at the National Institute of Diabetes and Digestive and Kidney
Diseases. Eight years ago, Baier identified a genetic variation in the Pimas associated with slowed metabolism and
increased glucose conservation. Researchers think that the gene helped Pima ancestors survive food shortages.
Though most of us are not Pimas, our own hunter-gatherer forebears would also have needed to survive food
shortages and scarcity—conditions that favor the evolution of similar fat-storing mechanisms, which are a problem in
times of plenty.
Abstract or Summary of the Article:
In the past, our ancestors, had genes that provided an advantage to their survival in the world of the
hunter and gathers. Conditions like ADHD, high blood pressure, lactose intolerance, and obesity have all
genetic connections in the past have been an adaptation that allowed people to survive better in their
world of limited food sources. ADHD provides individuals with more impulsivity and seeking new and
better resources would be an advantage to people wandering for food. High blood pressure would be the
result of individuals would need to obtain salt and retain the right amount of sodium. As food came and
went without consistency this would be very important gene to possess. Farming and agriculture would
have changed the collection and availability of food for communities. This environmental change could
favor individuals who were lactose tolerant; therefore, lactose intolerance is a relic of our past. Finally
obesity gene would be a benefit in places where food sources were in short supply. Slower metabolism
and increase in glucose conservation would benefit hunter-gatherers however, now they lead to
increased obesity and diabetes.
Connections to Class Content:
Proteins are the product of our genetic code and variations on that code would determine which trait we
would inherit. Lactase for example, is an enzyme that breaks down lactose, so if someone has inherited a
trait or code that prevents them from producing lactase, they would be lactose intolerant. As the culture
changed from hunter-gatherers to farms, there were more milk products available as a source of nutrients
and this environmental change would favour individuals with the gene for lactase. Over many
generations, this variation or gene would become more and more dominant in the gene pool as it
provides individuals with an advantage or an adaptation as they could eat more variety of food. The same
can be said about the genes for ADHD, retaining salt (high blood pressure), and storing energy (obesity).
Societal & Technological Implications:
By understanding the origin and purpose of genes, and the proteins that they produce, can help society,
medical professionals, and the general population identify increasing risk factors and come up with
preventative measures. Gene testing and therapy can also be something that could help or assist society
in treating or helping decrease the stress of ADHD behaviours, diseases related to high blood pressure,
diabetes, and other food intolerances.
Personal or Ethical Views:
Knowledge of a person’s genetics may lead to discrimination against certain genetic populations or
individuals by insurance companies or employers, and pharmaceutical companies could take advantage
of individuals who may overreact to the potential that their genes provide.
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1st Paragraph: Abstract/Summary
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3rd Paragraph: Societal and Technological Impacts
4th Paragraph: Ethical or Religious Impacts
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