Interactive atlas of genetic history

Scientists have mapped the effects of war, colonization, trade, migration and slavery on the genetic mixing of humans over the bulk of recorded history and created an online interactive atlas of humanity's genetic history. In a paper published in the journal Science, researchers detailed the genetic mixing between 95 populations across Europe, Africa, Asia and South America during 100 historical events over the last 4,000 years. The events include:

• The expansion of the Mongol empire by Genghis Khan, right. Traces of Mongol DNA in Pakistan's Hazara people support accounts that the Hazara descended from the warriors.

• In populations surrounding the Arabian Sea, researchers detected mixing with sub-Saharan Africans between A.D. 890 and 1754. That period seemed to coincide with Arab expansion and slave trade, the authors said.

• The researchers found mixing that escaped the notice of historians. "The DNA of the Tu people in modern China suggests that in around (A.D.) 1200, Europeans similar to modern Greeks mixed with an otherwise Chinese-like population," said co-author Simon Myers, a bioinformatics and statistics expert at Oxford University. Researchers analyzed genome data from 1,490 individuals. To see the map,

Freud's hysteria idea may be right

Sigmund Freud may have been right about repressed memories causing hysteria. Scientists at King's College London and the University of Melbourne have found, using brain scans, that psychological stress may be to blame for unexplained physical symptoms, including paralysis and seizures.

Patients showed differences in brain activity when they recalled traumatic memories compared with healthy volunteers in a study published in JAMA Psychiatry. Besides helping to explain one of the most common complaints seen by neurologists, the research may lead to new treatment approaches for patients whose symptoms were often written off by doctors in the past.

The scientists used functional magnetic resonance imaging, or fMRI, to trace changes in blood flow to areas of the brain while participants were probed about their pasts, yielding anatomical and functional views of their brains. Doctors have never before found a neurological basis for the condition — the brains, nerves and muscles of patients all appeared to be normal — leading them to suspect that the patients are making up their illness, said Richard Kanaan, a professor of psychiatry at the University of Melbourne and a coauthor of the study.

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