Before Arguing About DNA Tests, Learn the Science Behind Them

Posted in Articles, Health/Medicine/Genetics, Media Archive, Native Americans/First Nation, Politics/Public Policy on 2018-10-25 00:51Z by Steven

Before Arguing About DNA Tests, Learn the Science Behind Them

The New York Times
2018-10-18

Carl Zimmer


Senator Elizabeth Warren’s DNA test results indicated that she had a Native American ancestor several generations ago.
Bridget Bennett for The New York Times

Our genetic code cannot be treated as a matter of simple fractions.

People have always told stories about their ancestral origins. But now millions of people are looking at their DNA to see if those stories hold up. While genetic tests can indeed reveal some secrets about our family past, we can also jump to the wrong conclusions from their results.

The reception of Senator Elizabeth Warren’s DNA results is a textbook case in this confusion…

…Slavery, too, led to an obsession with increasingly tiny fractions of ancestral blood, reaching the absurd extreme of the “one drop” rule. A single black ancestor — no matter how far back in the family tree, no matter how tiny the mythical drop of blood he or she contributed — was enough to make a person black…

…But DNA is not a liquid that can be divided down into microscopic drops. It’s a string-like molecule, arranged into 23 pairs of chromosomes, that gets passed down through the generations in a counterintuitive way.

Eggs and sperm randomly end up with one copy of each chromosome, coming either from a person’s mother or father. In the process, some DNA can shuffle from one chromosome to its partner. That means we inherit about a quarter of our DNA from each grandparent — but only on average. Any one person may inherit more DNA from one grandparent and less from another.

Over generations, this randomness can lead to something remarkable. Look back far enough in your family tree, and you’ll encounter ancestors from whom you inherit no DNA at all…

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A Single Migration From Africa Populated the World, Studies Find

Posted in Africa, Articles, Health/Medicine/Genetics, History, Media Archive on 2016-09-25 14:38Z by Steven

A Single Migration From Africa Populated the World, Studies Find

The New York Times
2016-09-21

Carl Zimmer


The KhoiSan, hunter-gatherers living today in southern Africa, above, are among hundreds of indigenous people whose genetic makeup has provided new clues to human prehistory.
Credit: Eric Laforgue/Gamma-Rapho, via Getty Images

Modern humans evolved in Africa roughly 200,000 years ago. But how did our species go on to populate the rest of the globe?

The question, one of the biggest in studies of human evolution, has intrigued scientists for decades. In a series of extraordinary genetic analyses published on Wednesday, researchers believe they have found an answer.

In the journal Nature, three separate teams of geneticists survey DNA collected from cultures around the globe, many for the first time, and conclude that all non-Africans today trace their ancestry to a single population emerging from Africa between 50,000 and 80,000 years ago.

“I think all three studies are basically saying the same thing,” said Joshua M. Akey of the University of Washington, who wrote a commentary accompanying the new work. “We know there were multiple dispersals out of Africa, but we can trace our ancestry back to a single one.”…

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Tales of African-American History Found in DNA

Posted in Articles, Health/Medicine/Genetics, History, Media Archive, Slavery, United States on 2016-05-29 21:06Z by Steven

Tales of African-American History Found in DNA

The New York Times
2016-05-27

Carl Zimmer

The history of African-Americans has been shaped in part by two great journeys.

The first brought hundreds of thousands of Africans to the southern United States as slaves. The second, the Great Migration, began around 1910 and sent six million African-Americans from the South to New York, Chicago and other cities across the country.

In a study published on Friday, a team of geneticists sought evidence for this history in the DNA of living African-Americans. The findings, published in PLOS Genetics, provide a map of African-American genetic diversity, shedding light on both their history and their health.

Buried in DNA, the researchers found the marks of slavery’s cruelties, including further evidence that white slave owners routinely fathered children with women held as slaves.

And there are signs of the migration that led their descendants away from such oppression: Genetically related African-Americans are distributed closely along the routes they took to leave the South, the scientists discovered…

…The history of African-Americans poses special challenges for geneticists. During the slave trade, their ancestors were captured from genetically diverse populations across a portion of West Africa. Adding to the complexity is the fact that living African-Americans also may trace some of their ancestry to Europeans and Native Americans…

…Most of the Native American DNA identified by Dr. Gravel and his colleagues in African-Americans occurs now in tiny chunks. The scientists concluded that most of the mingling between Africans and Native Americans took place soon after the first slaves arrived in the American colonies in the early 1600s.

The European DNA in African-Americans, on the other hand, occurs in slightly longer chunks, indicating a more recent origin. Dr. Gravel and his colleagues estimate that its introduction dates to the decades before the Civil War

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Agriculture Linked to DNA Changes in Ancient Europe

Posted in Articles, Europe, Health/Medicine/Genetics, Media Archive on 2015-11-24 16:26Z by Steven

Agriculture Linked to DNA Changes in Ancient Europe

The New York Times
2015-11-23

Carl Zimmer

The agricultural revolution was one of the most profound events in human history, leading to the rise of modern civilization. Now, in the first study of its kind, an international team of scientists has found that after agriculture arrived in Europe 8,500 years ago, people’s DNA underwent widespread changes, altering their height, digestion, immune system and skin color.

Researchers had found indirect clues of some of these alterations by studying the genomes of living Europeans. But the new study, they said, makes it possible to see the changes as they occurred over thousands of years.

“For decades we’ve been trying to figure out what happened in the past,” said Rasmus Nielsen, a geneticist at the University of California, Berkeley, who was not involved in the new study. “And now we have a time machine.”

…Dr. Reich and his colleagues also tracked changes in the color of European skin.

The original hunter-gatherers, descendants of people who had come from Africa, had dark skin as recently as 9,000 years ago. Farmers arriving from Anatolia were lighter, and this trait spread through Europe. Later, a new gene variant emerged that lightened European skin even more.

Why? Scientists have long thought that light skin helped capture more vitamin D in sunlight at high latitudes. But early hunter-gatherers managed well with dark skin. Dr. Reich suggests that they got enough vitamin D in the meat they caught.

He hypothesizes that it was the shift to agriculture, which reduced the intake of vitamin D, that may have triggered a change in skin color…

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White? Black? A Murky Distinction Grows Still Murkier

Posted in Anthropology, Articles, Health/Medicine/Genetics, History, Latino Studies, Law, Media Archive, Native Americans/First Nation, Slavery, United States on 2014-12-24 17:50Z by Steven

White? Black? A Murky Distinction Grows Still Murkier

The New York Times
2014-12-24

Carl Zimmer

In 1924, the State of Virginia attempted to define what it means to be white.

The state’s Racial Integrity Act, which barred marriages between whites and people of other races, defined whites as people “whose blood is entirely white, having no known, demonstrable or ascertainable admixture of the blood of another race.”

There was just one problem. As originally written, the law would have classified many of Virginia’s most prominent families as not white, because they claimed to be descended from Pocahontas.

So the Virginia legislature revised the act, establishing what came to be known as the “Pocahontas exception.” Virginians could be up to one-sixteenth Native American and still be white in the eyes of the law.

People who were one-sixteenth black, on the other hand, were still black.

In the United States, there is a long tradition of trying to draw sharp lines between ethnic groups, but our ancestry is a fluid and complex matter. In recent years geneticists have been uncovering new evidence about our shared heritage, and last week a team of scientists published the biggest genetic profile of the United States to date, based on a study of 160,000 people…

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DNA Double Take

Posted in Articles, Health/Medicine/Genetics, Media Archive on 2014-01-03 18:52Z by Steven

DNA Double Take

The New York Times
2013-09-16

Carl Zimmer

From biology class to “C.S.I.,” we are told again and again that our genome is at the heart of our identity. Read the sequences in the chromosomes of a single cell, and learn everything about a person’s genetic information — or, as 23andme, a prominent genetic testing company, says on its Web site, “The more you know about your DNA, the more you know about yourself.”

But scientists are discovering that — to a surprising degree — we contain genetic multitudes. Not long ago, researchers had thought it was rare for the cells in a single healthy person to differ genetically in a significant way. But scientists are finding that it’s quite common for an individual to have multiple genomes. Some people, for example, have groups of cells with mutations that are not found in the rest of the body. Some have genomes that came from other people…

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