Monkey see, monkey recall – at least for a couple of minutes.
Ben Basile of Emory University in Atlanta placed five rhesus monkeys in front of a touchscreen that briefly showed a blue square and two red ones. After an interval of up to two minutes, the blue square reappeared in a different place, and the monkeys were prompted to replicate the pattern in its new position by tapping the screen to place red squares.
Their success rate was significantly better than chance, showing for the first time that they are able to recall things from recent memory. This is more advanced than recognizing a familiar object, and it could be a precursor to long-term memory.
The study could help resolve a longstanding question, says Howard Eichenbaum of Boston University. “There is a big controversy over whether recollection and familiarity are [run by] different processes, or just reflect the strength of the memory,” he says.
The question arises because most memory tests can be solved using either recollection or familiarity. But the ability to recognize familiar objects does not help solve Basile’s test, opening the possibility of using it to determine the neurological pathways that govern recollection alone.
As humans migrated out of Africa around 50,000 years ago and moved across the planet, evolution may have latched onto a gene linked to risk-taking and adventurousness. This idea, first put forward a decade ago by Chuansheng Chen at the University of California at Irvine, was originally met with skepticism. Now Luke Matthews of Harvard University and Paul Butler of Boston University have shown that a link between two versions of a specific gene and ancient migration patterns stands up to rigorous analysis.
The DRD4 gene codes for a dopamine receptor in the brain. It exists in several versions, or alleles, and studies have shown that people tend to have slightly different personality traits depending on which they have. The 4R allele, for instance, is associated with being even-tempered, reflective and prudent. The less common 7R and 2R versions have been linked to impulsive and exploratory behavior, risk-taking and the ability to shrug off new situations. Matthews and Butler think that migrants with these versions were better able to deal with dangerous, fluctuating situations and more likely to survive and reproduce.
They looked at the frequency of 7R and 2R in 18 indigenous populations spread along the routes humans took from Africa to Europe, Asia and the Americas. The farther away from Africa they were, the more likely they were to have one of these two versions. The problem with Chen’s 1999 study was that populations can share alleles by chance, which might create the illusion of a link between, say, distance traveled and certain alleles. To overcome this, Matthews and Butler modeled how alleles show up in populations. They discovered that the distribution of 7R and 2R is not random, and they were able to demonstrate a statistically significant link between these alleles and migration.
The study suggests that some small portion of the behaviors that characterize populations may be attributable to genetics and that cultural actions such as mass migration can modify our genes, says Matthews. Researchers are beginning to play with the idea that our culture could be influencing evolution, says Robert Moyzis, also of UC Irvine. He has shown that 7R arose as a rare mutation 40,000 to 50,000 years ago, after the initial departures from Africa, then spread rapidly in human populations. The 2R allele is a modified version that arose in Asia less than 10,000 years ago.
He has also shown that people with attention-deficit hyperactivity disorder are twice as likely as others to have the 7R allele. He thinks that some actions that are considered symptoms of ADHD, such as rapidly shifting focus and quick movements, are actually survival traits that were selected for during the migration out of Africa.
These articles were produced by New Scientist magazine and can be read at www.newscientist.com.