Our Brains Are Shrinking. Are We Getting Dumber?

January 2, 2011

When it comes to brain size, bigger doesn’t always mean better. As humans continue to evolve, scientists say our brains are actually getting smaller.

The downsizing of human brains is an evolutionary fact that took science writer Kathleen McAuliffe by surprise.

“I said, ‘What?  I thought it was getting bigger!'” she tells NPR’s Jacki Lyden. That was the story up to 20,000 years ago, she learned. Then, the brains of our ancestors reversed course and started getting smaller — and they’ve been shrinking ever since.

Cro-Magnon man, who lived in Europe 20,000 to 30,000 years ago, had the biggest brains of any human species.  In comparison, today’s human brain is about 10 percent smaller. It’s a chunk of brain matter “roughly equivalent to a tennis ball in size,” McAuliffe says.

The experts aren’t sure about the implications of this evolutionary trend.  Some think it might be a dumbing-down process. One cognitive scientist, David Geary, argues that as human society grows increasingly complex, individuals don’t need to be as intelligent in order to survive and reproduce.

But not all researchers are so pessimistic. Brian Hare, an anthropologist at the Duke University Institute for Brain Sciences, thinks the decrease in brain size is actually an evolutionary advantage.

The Domesticated Brain

“A smaller brain is the signature of selection against aggression,” Hare tells Lyden.  “Another way to say that is an increase in tolerance.”

Hare says when a population selects against aggression, they can be considered to be domesticated.  And for a variety of domesticated animals like apes, dogs or turkeys, you can see certain physical characteristics emerge. Among these traits are a lighter and more slender skeleton, a flattened forehead — and decreased brain size

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Evolutionary Surprise: Eight Percent of Human Genetic Material Comes from a Virus

ScienceDaily (Jan. 8, 2010) — About eight percent of human genetic material comes from a virus and not from our ancestors, according to researchers in Japan and the U.S.

The study, and an accompanying News & Views article by University of Texas at Arlington biology professor Cédric Feschotte, is published in the journal Nature.

The research showed that the genomes of humans and other mammals contain DNA derived from the insertion of bornaviruses, RNA viruses whose replication and transcription takes place in the nucleus. Feschotte wrote on recent research led by Professor Keizo Tomonaga at Osaka University in Japan. Feschotte said this virally transmitted DNA may be a cause of mutation and psychiatric disorders such as schizophrenia and mood disorders.

In his article, Feschotte speculates about the role of such viral insertions in causing mutations with evolutionary and medical consequences.

The assimilation of viral sequences into the host genome is a process referred to as endogenization. This occurs when viral DNA integrates into a chromosome of reproductive cells and is subsequently passed from parent to offspring. Until now, retroviruses were the only viruses known to generate such endogenous copies in vertebrates. But Feschotte said that scientists have found that non-retroviral viruses called bornaviruses have been endogenized repeatedly in mammals throughout evolution.

Bornavirus (BDV) owes its name to the town of Borna, Germany, where a virus epidemic in 1885 wiped out a regiment of cavalry horses. BDV infects a range of birds and mammals, including humans. It is unique because it infects only neurons, establishing a persistent infection in its host’s brain, and its entire life cycle takes place in the nucleus of the infected cells. Feschotte said this intimate association of BDV with the cell nucleus prompted researchers to investigate whether bornaviruses may have left behind a record of past infection in the form of endogenous elements. They searched the 234 known eukaryotic genomes (those genomes that have been fully sequenced) for sequences that are similar to that of BDV. “The researchers unearthed a plethora of endogenous Borna-like N (EBLN) elements in many diverse mammals, ” Feschotte said.

The scientists also were able to recover spontaneous BDV insertions in the chromosomes of human cultured cells persistently infected by BVD.Based on these data, Feschotte proposes that BDV insertions could be a source of mutations in the brain cells of infected individuals.

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Male Or Female? Coloring Provides Gender Cues

Our brain is wired to identify gender based on facial cues and coloring, according to a new study published in the Journal of Vision. Psychology Professor Frédéric Gosselin and his Université de Montréal team found the luminescence of the eyebrow and mouth region is vital in rapid gender discrimination.
“As teenagers, dimorphism (systematic difference between sexes) increases in the nose, chin, mouth, jaw, eyes and general shape of faces,” says Nicolas Dupuis-Roy, lead author of the study. “Yet we aren’t conscious of how our brain recognizes those differences.”

To discover those reference points, Dupuis-Roy and colleagues showed photos of 300 Caucasian faces to some 30 participants. Subjects were asked to identify gender based on images where parts of faces were concealed using a technology called Bubbles.

The investigation found that eyes and mouths, specifically their subtle shading or luminance, are paramount in identifying gender. Unlike previous studies, which found the gap between the eyelid and eyebrow as essential in gender ID, this investigation found the shades of reds and greens around mouths and eyes led to faster gender discrimination.

“Studies have shown that an androgynous face is considered male if the skin complexion is redder, and considered female if the complexion is greener,” says Dupuis-Roy. “However, it is the opposite for the mouth. A woman’s mouth is usually redder. Our brain interprets this characteristic as female.”

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Some People Really ‘Never Forget A Face:’ Understanding Extraordinary Face Recognition Ability

ScienceDaily (May 20, 2009) — Some people say they never forget a face, a claim now bolstered by psychologists at Harvard University who’ve discovered a group they call “super-recognizers”: those who can easily recognize someone they met in passing, even many years later.

The new study suggests that skill in facial recognition might vary widely among humans. Previous research has identified as much as 2 percent of the population as having “face-blindness,” or prosopagnosia, a condition characterized by great difficulty in recognizing faces. For the first time, this new research shows that others excel in face recognition, indicating that the trait could be on a spectrum, with prosopagnosics on the low end and super-recognizers at the high end.

The research is published in Psychonomic Bulletin & Review, and was led by Richard Russell, a postdoctoral researcher in the Department of Psychology at Harvard, with co-authors Ken Nakayama, Edgar Pierce Professor of Psychology at Harvard, and Brad Duchaine of the University College London.

The research involved administering standardized face recognition tests. The super-recognizers scored far above average on these tests—higher than any of the normal control subjects.
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I never forget a Face! NEVER. even when the face ages I still remember it. weird

Human Brains Make Their Own ‘Marijuana’

ScienceDaily (Apr. 20, 2009) — U.S. and Brazilian scientists have discovered that the brain manufactures proteins that act like marijuana at specific receptors in the brain itself. This discovery may lead to new marijuana-like drugs for managing pain, stimulating appetite, and preventing marijuana abuse.”Ideally, this development will lead to drugs that bind to and activate the THC receptor, but are devoid of the side effects that limit the usefulness of marijuana,” said Lakshmi A. Devi of the Department of Pharmacology and Systems Therapeutics at Mount Sinai School of Medicine in New York and one of the senior researchers involved in the study. “It would be helpful to have a drug that activated or blocked the THC receptor, and our findings raise the possibility that this will lead to effective drugs with fewer side effects.”

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