Directions: After carefully reading the articles, provide a detailed answer to the following questions. Make
sure to either use direct quotes from the articles correctly or put the information into your own words.
Based on selected National Geographic Articles
(I posted pdf files on MyMtech so you don’t have to sign up with National Geographic unless you choose to)
The Surprising Way Saliva Brought These Six Strangers Together
Siblings Can Have Surprisingly Different DNA Ancestry. Here's Why.
These Twins, One Black and One White, Will Make You Rethink Race
There's No Scientific Basis for Race--It's a made-up label
1. (2 pts) Everyone profiled in these articles has had DNA testing through National Geographic's DNA Ancestry Kit.
Explain what this type of DNA testing is and why broad DNA testing is now possible.
2. (5 pts) What is meant by "DNA Ancestry" as the term is used in these articles? Explain how the six people profiled in
"The Surprising Way Saliva Brought These Six Strangers Together" can be unrelated yet share the same "DNA Ancestry".
3. (5 pts) In terms of your understanding of the process of Meiosis and how new genetic combinations (diversity) can
arise, explain why the two sets of twins discussed can have different traits (phenotypes) and different DNA Ancestry.
Refer to the articles "Siblings Can Have Surprisingly Different DNA Ancestry. Here's Why" and "These Twins, One Black
and One White, Will Make You Rethink Race".
4. (3 pts) Based on the explanation in the articles, why else (apart from what happens in Meiosis) might biological family
member's DNA testing results turn out different from one another?
5. (5 pts) What is an example of a quantitative trait discussed in the article "There's No Scientific Basis for Race—It's a
Made-Up Label". What is a quantitative trait? What causes the phenotypic variation seen in such traits? Provide and
example from the article.
Instructor: Anna Nugent
These Twins Will Make You Rethink Race
Marcia and Millie Biggs say they’ve never been subjected to racism—just curiosity and
surprise that twins could have such different skin colors.
BY PATRICIA EDMONDS
W H E N A M A N D A W A N K L I N and Michael Biggs fell in love, they “didn’t give a toss” about the
challenges they might face as a biracial couple, Amanda says. “What was more important was what we wanted
They settled down in Birmingham, England, eager to start a family. On July 3, 2006, Amanda gave birth to
fraternal twin girls, and the ecstatic parents gave their daughters intertwined names: One would be Millie
Marcia Madge Biggs, the other Marcia Millie Madge Biggs.
From a young age the girls had similar features but very different color schemes. Marcia had light brown hair
and fair skin like her English-born mother. Millie had black hair and brown skin like her father, who’s of
Jamaican descent. “We never worried about it; we just accepted it,” Michael says.
“When they were first born,” Amanda recalls, “I would be pushing them in the pram, and people would look at
me and then look at my one daughter and then look at my other daughter. And then I’d get asked the question:
‘Are they twins?’”
“‘But one’s white and one’s black.’”
“Yes. It’s genes.”
People who commented on the girls weren’t openly hostile or judgmental—just very curious, Amanda says. And
then “as time went on, people just saw the beauty in them.”
Amanda, who works as a home-care aide, calls Millie and Marcia her “one in a million” miracle. But it’s not that
rare that a biracial couple would have fraternal twins who each look more like one parent than the other, says
statistical geneticist Alicia Martin.
Fraternal twins account for about one in 100 births. When a biracial couple has fraternal twins, the traits that
emerge in each child depend on numerous variables, including “where the parents’ ancestors are from and
complex pigment genetics,” says Martin, a postdoctoral research fellow at the Broad Institute in Cambridge,
And research on skin color is further complicated by a history of “study biases that mean we know more about
what makes lighter skin light than what makes darker skin dark,” she says.
In genetic terms, skin color “is not a binary trait” with only two possibilities, Martin notes. “It’s a quantitative
trait, and everyone has some gradient on this spectrum.”
Historically, when humans have drawn lines of identity—separating Us from Them—they’ve often relied on
skin color as a proxy for race. But the 21st-century understanding of human genetics tells us that the whole idea
of race is a human invention.
Modern science confirms “that the visible differences between peoples are accidents of history”—the result of
mutations, migrations, natural selection, the isolation of some populations, and interbreeding among others,
writes science journalist Elizabeth Kolbert. They are not racial differences because the very concept of race—to
quote DNA-sequencing pioneer Craig Venter—“has no genetic or scientific basis.”
And yet 50 years after the assassination of Rev. Martin Luther King, Jr., racial identity has reemerged as a
fundamental dividing line in our world.
We’re devoting the April issue of National Geographic to the complicated issue of race.
The Race Issue includes a story about how scientific ideas of race originated, a letter from our editor exploring
National Geographic’s own checkered history on race, and a video-driven feature documenting the
phenomenon of black men getting stopped by police while driving.
This month’s issue is just a starting point. We’re doing stories on the evolving identities of key ethnic, religious,
and racial groups throughout 2018.
They Think We’re Just Best Friends
The twins, for their part, understand quite clearly what racism is. “Racism is where somebody judges you by
your color and not by your actual self,” Millie says. Marcia describes racism as “a negative thing, because it can
hurt people’s feelings.”
Michael, who owns an auto-repair business, says he’s faced hostility at times because of the color of his skin.
He vividly recalls an episode from his youth when a car full of men sped by and shouted slurs at him and his
“But it’s a different time now,” Michael says. Neither he nor Amanda has ever witnessed racist behavior toward
the girls. And both Millie and Marcia say that they’ve never sensed racism when people note the contrast in
“When people see us, they think that we’re just best friends,” Marcia says. “When they learn that we’re twins,
they’re kind of shocked because one’s black and one’s white.”
But when the twins are asked about their differences, they mention something else entirely. “Millie likes things
that are girlie. She likes pink and all of that,” Marcia says. “I don’t like the color pink; I’m a tomboy. People are
made how they are.”
Even when the twins’ mother, Amanda Wanklin,
dressed them alike, there was no mistaking one for
the other.P H O T O G R A P H C O U R T E S Y
There’s No Scientific Basis for Race—It's a Made-Up Label
It's been used to define and separate people for millennia. But the concept of race is not
grounded in genetics.
BY ELIZABETH KOLBERT
PHOTOGRAPHS BY ROBIN HAMMOND
I N T H E F I R S T half of the 19th century, one of America’s most prominent scientists was a doctor named
Samuel Morton. Morton lived in Philadelphia, and he collected skulls.
He wasn’t choosy about his suppliers. He accepted skulls scavenged from battlefields and snatched from
catacombs. One of his most famous craniums belonged to an Irishman who’d been sent as a convict to
Tasmania (and ultimately hanged for killing and eating other convicts). With each skull Morton performed the
same procedure: He stuffed it with pepper seeds—later he switched to lead shot—which he then decanted to
ascertain the volume of the braincase.
Morton believed that people could be divided into five races and that these represented separate acts of
creation. The races had distinct characters, which corresponded to their place in a divinely determined
hierarchy. Morton’s “craniometry” showed, he claimed, that whites, or “Caucasians,” were the most intelligent
of the races. East Asians—Morton used the term “Mongolian”—though “ingenious” and “susceptible of
cultivation,” were one step down. Next came Southeast Asians, followed by Native Americans. Blacks, or
“Ethiopians,” were at the bottom. In the decades before the Civil War, Morton’s ideas were quickly taken up by
the defenders of slavery.
“He had a lot of influence, particularly in the South,” says Paul Wolff Mitchell, an anthropologist at the
University of Pennsylvania who is showing me the skull collection, now housed at the Penn Museum. We’re
standing over the braincase of a particularly large-headed Dutchman who helped inflate Morton’s estimate of
Caucasian capacities. When Morton died, in 1851, the Charleston Medical Journal in South Carolina praised
him for “giving to the negro his true position as an inferior race.”
Today Morton is known as the father of scientific racism. So many of the horrors of the past few centuries can
be traced to the idea that one race is inferior to another that a tour of his collection is a haunting experience. To
an uncomfortable degree we still live with Morton’s legacy: Racial distinctions continue to shape our politics,
our neighborhoods, and our sense of self.
This is the case even though what science actually has to tell us about race is just the opposite of what Morton
Morton thought he’d identified immutable and inherited differences among people, but at the time he was
working—shortly before Charles Darwin put forth his theory of evolution and long before the discovery of
DNA—scientists had no idea how traits were passed on. Researchers who have since looked at people at the
genetic level now say that the whole category of race is misconceived. Indeed, when scientists set out to
assemble the first complete human genome, which was a composite of several individuals, they deliberately
gathered samples from people who self-identified as members of different races. In June 2000, when the
results were announced at a White House ceremony, Craig Venter, a pioneer of DNA sequencing, observed,
“The concept of race has no genetic or scientific basis.”
Over the past few decades, genetic research has revealed two deep truths about people. The first is that all
humans are closely related—more closely related than all chimps, even though there are many more humans
around today. Everyone has the same collection of genes, but with the exception of identical twins, everyone
has slightly different versions of some of them. Studies of this genetic diversity have allowed scientists to
reconstruct a kind of family tree of human populations. That has revealed the second deep truth: In a very real
sense, all people alive today are Africans.
Our species, Homo sapiens, evolved in Africa—no one is sure of the exact time or place. The most recent fossil
find, from Morocco, suggests that anatomically modern human features began appearing as long as 300,000
years ago. For the next 200,000 years or so, we remained in Africa, but already during that period, groups
began to move to different parts of the continent and become isolated from one another—in effect founding
In humans, as in all species, genetic changes are the result of random mutations—tiny tweaks to DNA, the code
of life. Mutations occur at a more or less constant rate, so the longer a group persists, handing down its genes
generation after generation, the more tweaks these genes will accumulate. Meanwhile, the longer two groups
are separated, the more distinctive tweaks they will acquire.
By analyzing the genes of present-day Africans, researchers have concluded that the Khoe-San, who now live in
southern Africa, represent one of the oldest branches of the human family tree. The Pygmies of central Africa
also have a very long history as a distinct group. What this means is that the deepest splits in the human family
aren’t between what are usually thought of as different races—whites, say, or blacks or Asians or Native
Americans. They’re between African populations such as the Khoe-San and the Pygmies, who spent tens of
thousands of years separated from one another even before humans left Africa.
All non-Africans today, the genetics tells us, are descended from a few thousand humans who left Africa
maybe 60,000 years ago. These migrants were most closely related to groups that today live in East Africa,
including the Hadza of Tanzania. Because they were just a small subset of Africa’s population, the migrants
took with them only a fraction of its genetic diversity.
Somewhere along the way, perhaps in the Middle East, the travelers met and had sex with another human
species, the Neanderthals; farther east they encountered yet another, the Denisovans. It’s believed that both
species evolved in Eurasia from a hominin that had migrated out of Africa much earlier. Some scientists also
believe the exodus 60,000 years ago was actually the second wave of modern humans to leave Africa. If so,
judging from our genomes today, the second wave swamped the first.
In what was, relatively speaking, a great rush, the offspring of all these migrants dispersed around the world.
By 50,000 years ago they had reached Australia. By 45,000 years ago they’d settled in Siberia, and by 15,000
years ago they’d reached South America. As they moved into different parts of the world, they formed new
groups that became geographically isolated from one another and, in the process, acquired their own
distinctive set of genetic mutations.
Most of these tweaks were neither helpful nor harmful. But occasionally a mutation arose that turned out to be
advantageous in a new setting. Under the pressure of natural selection, it spread quickly through the local
population. At high altitudes, for instance, oxygen levels are low, so for people moving into the Ethiopian
highlands, Tibet, or the Andean Altiplano, there was a premium on mutations that helped them cope with the
rarefied air. Similarly, Inuit people, who adopted a marine-based diet high in fatty acids, have genetic tweaks
that helped them adapt to it.
Sometimes it’s clear that natural selection has favored a mutation, but it’s not clear why. Such is the case with a
variant of a gene called EDAR (pronounced ee-dar). Most people of East Asian and Native American ancestry
possess at least one copy of the variant, known as 370A, and many possess two. But it’s rare among people of
African and European descent.
At the University of Pennsylvania’s Perelman School of Medicine, geneticist Yana Kamberov has equipped mice
with the East Asian variant of EDAR in hopes of understanding what it does. “They’re cute, aren’t they?” she
says, opening the cage to show me. The mice look ordinary, with sleek brown coats and shiny black eyes. But
examined under a microscope, they are different from their equally cute cousins in subtle yet significant ways.
Their hair strands are thicker; their sweat glands are more numerous; and the fat pads around their mammary
glands are smaller.
Kamberov’s mice help explain why some East Asians and Native Americans have thicker hair and more sweat
glands. (EDAR’s effect on human breasts is unclear.) But they don’t provide an evolutionary reason. Perhaps,
Kamberov speculates, the ancestors of contemporary East Asians at some point encountered climate conditions
that made more sweat glands useful. Or maybe thicker hair helped them ward off parasites. Or it could be that
370A produced other benefits she’s yet to discover and the changes she has identified were, in effect, just
tagalongs. Genetics frequently works like this: A tiny tweak can have many disparate effects. Only one may be
useful—and it may outlive the conditions that made it so, the way families hand down old photos long past the
point when anyone remembers who’s in them.
“Unless you have a time machine, you’re not going to know,” Kamberov sighs.
DNA is often compared to a text, with the letters standing for chemical bases—A for adenine, C for
cytosine, G for guanine, and T for thymine. The human genome consists of three billion base pairs—page after
page of A’s, C’s, G’s, and T’s—divided into roughly 20,000 genes. The tweak that gives East Asians thicker hair
is a single base change in a single gene, from a T to a C.
Similarly, the mutation that’s most responsible for giving Europeans lighter skin is a single tweak in a gene
known as SLC24A5, which consists of roughly 20,000 base pairs. In one position, where most sub-Saharan
Africans have a G, Europeans have an A. About a decade ago a pathologist and geneticist named Keith Cheng,
at Penn State College of Medicine, discovered the mutation by studying zebrafish that had been bred to have
lighter stripes. The fish, it turned out, possessed a mutation in a pigment gene analogous to the one that is
mutated in Europeans.
Studying DNA extracted from ancient bones, paleogeneticists have found that the G-to-A substitution was
introduced into western Europe relatively recently—about 8,000 years ago—by people migrating from the
Middle East, who also brought a newfangled technology: farming. That means the people already in Europe—
hunter-gatherers who created the spectacular cave paintings at Lascaux, for example—probably were not white
but brown. The ancient DNA suggests that many of those dark-skinned Europeans also had blue eyes, a
combination rarely seen today.
“What the genetics shows is that mixture and displacement have happened again and again and that our
pictures of past ‘racial structures’ are almost always wrong,” says David Reich, a Harvard University
paleogeneticist whose new book on the subject is called Who We Are and How We Got Here. There are no
fixed traits associated with specific geographic locations, Reich says, because as often as isolation has created
differences among populations, migration and mixing have blurred or erased them.
Across the world today, skin color is highly variable. Much of the difference correlates with latitude. Near the
Equator lots of sunlight makes dark skin a useful shield against ultraviolet radiation; toward the poles, where
the problem is too little sun, paler skin promotes the production of vitamin D. Several genes work together to
determine skin tone, and different groups may possess any number of combinations of different tweaks.
Among Africans, some people, such as the Mursi of Ethiopia, have skin that’s almost ebony, while others, such
as the Khoe-San, have skin the color of copper. Many dark-skinned East Africans, researchers were surprised to
learn, possess the light-skinned variant of SLC24A5. (It seems to have been introduced to Africa, just as it was
to Europe, from the Middle East.) East Asians, for their part, generally have light skin but possess the darkskinned version of the gene. Cheng has been using zebrafish to try to figure out why. “It’s not simple,” he says.
When people speak about race, usually they seem to be referring to skin color and, at the same time, to
something more than skin color. This is the legacy of people such as Morton, who developed the “science” of
race to suit his own prejudices and got the actual science totally wrong. Science today tells us that the visible
differences between peoples are accidents of history. They reflect how our ancestors dealt with sun exposure,
and not much else.
“We oft ...
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