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WEDNESDAY, July 1, 2015 (HealthDay News) -- The less alike two parents are genetically, the taller and mentally sharper their kids tend to be, according to a new study of populations around the world.
Researchers said the findings, published in the journal Nature, suggest that humans evolved to favor height and quick thinking.
That may not sound surprising, experts said. But the work is "fascinating" in that it culled genetic information on more than 350,000 people from across the globe -- and found consistent patterns, said Dr. Martin Bialer, a medical geneticist who was not involved in the research.
That is, parents' genetic diversity was reliably linked to four traits in their kids: height; cognitive skills (such as the ability to learn, remember and problem-solve); educational attainment, and lung function. In each case, the more diverse two parents were, the better.
On the other hand, parents' genetic diversity did not matter much -- if at all -- when it came to blood pressure, cholesterol levels, body weight or other factors that have a big impact on common, chronic health conditions.
That does make sense, according to Bialer, who is based at the North Shore-LIJ Health System, in Great Neck, N.Y.
Health problems like diabetes, high blood pressure and heart disease typically arise later in life, Bialer noted. And human evolution is more concerned with the ability to create healthy children, and then survive long enough to raise them.
Jim Wilson, the senior researcher on the study, agreed.
"These risk factors mostly have their effect post-reproductively, and so would not be subject to so much natural selection," said Wilson, a senior lecturer in population and disease genetics at the University of Edinburgh in Scotland.
It has long been known that children born to closely related parents are at increased risk of rare genetic disorders. Charles Darwin was among the first to recognize that inbreeding reduces "evolutionary fitness," Wilson noted.
In fact, Darwin famously married his first cousin and wondered what effects that could have on his own children, Wilson said.
Yet all these years later, little is known about whether more-distant "relatedness" has any impact on human health and well-being.
This new research, Wilson said, "shows the power of large-scale genomic studies to answer fundamental questions about evolution -- indeed, questions that Darwin himself pondered."
For the study, Wilson and an international team of researchers analyzed genetic and health information on thousands of people from urban and rural areas across the globe.
The researchers examined each person's entire genetic makeup, looking for instances in which an individual had inherited identical copies of a gene from both parents.
When a person has few identical gene copies, it's unlikely that the two sides of the family are distantly related, according to Wilson. But as the number of identical copies goes up, the odds that a person's ancestors were related rise as well.
Bialer stressed that this was a broad population study, looking for statistical links between genetic diversity and certain human traits -- and aimed at evolutionary questions.
No one is suggesting that someone have a prospective mate's genome analyzed in the hopes of having tall, smart kids.
"This doesn't mean that for an individual, there's a significant effect on height or cognitive ability," Bialer said.
Wilson's team estimated, for example, that if two first cousins married, it could shave 1.2 centimeters (or less than half an inch) from their child's height.
And when it comes to the common medical conditions that plague modern society, the researchers said parents' relatedness may have little to no impact.
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SOURCES: Jim Wilson, D.Phil., senior lecturer, population and disease genetics, University of Edinburgh, Scotland; Martin Bialer, M.D., medical geneticist, North Shore-LIJ Health System, Great Neck, N.Y.; July 1, 2015, Nature, online