WHY WE ARE ALL BROTHERS AND SISTERS

Research shows that despite our ethnic and cultural differences, we are all brothers and sisters. People from distant lands have strikingly similar genetic traits. Scientists have long recognized that all human populations are genetically similar to one another. But recent studies go beyond this. They conclude that populations from different parts of the world share even more genetic similarities than had previously been assumed.

At the same time, researchers are finding that tiny differences in DNA can provide enough information to identify the geographic ancestry of individual men and women.

In one study, the largest of its kind to date, has implications for understanding ancient human migrations and for resolving the ongoing debate about the use of ancestry information in medical research. (1) According to Dr. Marcus Feldman of the School of Humanities and Social Sciences at Stanford University, "Different populations experience different rates of various diseases. To determine if someone is genetically susceptible to a particular disease, doctors will sometimes ask a patient, 'What is your ancestry?' But recent studies have raised the question of whether self-reported ancestry is a useful diagnostic tool, or whether it should be abandoned in favor of genetic testing."

The authors of the Stanford study conclude that a patient interview can, in fact, provide a useful, less invasive alternative for assessing individual disease risks. In their study, Dr. Feldman and his colleagues analyzed DNA samples obtained from 1,056 people from 52 populations in five major geographic regions of the world: Africa, Eurasia (Europe, the Middle East, Central and South Asia), East Asia, Oceania, and the Americas. In order to identify specific populations, the research team looked for "DNA microsatellites"--short segments of human DNA that occur in specific patterns, which are passed down from generation to generation. In the study, researchers analyzed 377 DNA microsatellites that population biologists routinely used as genetic markers. According to Dr. Feldman, "Each microsatellite had between four and 32 distinct types. Most were found in people from several continents, suggesting that only a tiny fraction of genetic traits are distinctive to specific populations. This means that visible differences between human groups--such as skin color and skull shape--result from differences in a very small proportion of genetic traits."

He notes that another way to view this, "is to remember that DNA is virtually identical in all human beings. Compare any two people, you'll find a DNA sequence that is about 99.9 percent identical." He adds that "In the less than one percent of the genome where genetic differences among individuals exist, it might seem intuitive that two people from different regions are likely to have more differences than are two people from the same region. But this is not the case. About 94 percent of genetic differences are among individuals of the same populations."

Dr. Feldman concludes that people from different lands have more genetic similarities than scientists previously thought.

Although populations are genetically quite similar, scientists have wanted to see if they could predict where an individual's ancestors came from through DNA analysis alone. To accomplish this, the Stanford team first removed the labels from all 1,056 DNA samples used in the study. As Dr. Feldman explains "We took the labels off of all the individuals so we didn't know where they came from. Then we asked the question, 'Can we look at the DNA and detect where groups of individuals form clusters that are genetically related to one another?'" The answer should be "Yes", the Stanford team predicted. This is because, while most genetic types are widely distributed geographically, the frequencies of these types vary around the world. The Stanford team applied a powerful statistical technique that uses many independent genes to detect the geographic patterns of ancestry in samples from any species. When applied to people, the technique proved remarkably successful. The research team accurately pinpointed the ancestral continent of virtually every individual from Africa, East Asia, Oceania, and the Americas.

People from Eurasia (including Europe, the Middle East, and Central and South Asia, were among the most difficult to assign ancestries. But as Dr. Feldman notes, "A complex history of migrations, conquests and trade over the past few thousand years is likely to be the cause for this difficulty." Interestingly, an exception was the Basques of Spain---a geographically and linguistically isolated population that was genetically distinguishable from other European groups.

DNA analysis confirmed what most of the Stanford study's 1,056 participants had said about their ancestry---a finding that lends credence to the argument that an individual's own family history can be a useful way of determining his or her genetic predisposition to disease. Dr. Feldman observes that "Some members of the medical community argue that doctors simply shouldn't ask patients about their ancestry because it has no genetic meaning. But our study finds that self-reported ancestry and genetic ancestry are largely coincident, so patient interviews can be very useful. On the one hand, grouping patients by genetic similarities will benefit future studies that will scan the entire human genome for potential genetic causes of disease. On the other hand, self-reported ancestry makes it easier to get information on environmental factors, cultural differences and behaviours which may be important risk factors for certain diseases."

The Stanford research also supports recent genetic studies of human migration, confirming migratory patterns between Europe and West Asia, Europe, Central America, and other continents as well. According to Drs. Mary Claire King and Arno Motulsky of the University of Washington in Seattle, "By sampling genotypes from people from all parts of the world, geneticists have reconstructed the major features of our history: Our ancient African origin, migrations out of Africa, movements and settlements throughout Eurasia and Oceania, and the peopling of the Americas."

We are all more closely related than we thought.

(1) Rosenberg, N., Pritchard, J., Weber, J., Cann, H., Kidd, K., Zhivotovsky, L., Feldman, M. (2202) Genetic Structure Of Human Populations. SCIENCE 298(5602):2381-2385.

 

 

Complete News Archives: 2003 January: The "Curse" That Won't Die 2002 December: Why is your face so red? November: How to be creative October: The Little Differences Between Men and Women September: The Mars Effect August: Weird mysteries of creative giants July: How many senses do we have? June: The Samson Syndrome May: Phantom Limb Syndrome April: Can we talk to the unborn? March: Movie Revelations February: Navel Secrets January: If Whales Can Do It? 2001 December: Body Odysseys of the Famous November: The Psychology of Smell October: Light, Colour and Music Therapy September: Three Brain Mysteries August: Baldness July News June: Laughing