Is altruism a genetic trait?
—Daniel Hall, Oceanside, Calif.

Nicholas R. Eaton, a doctoral student in psychology at Washington University in St. Louis, responds, writing in collaboration with professor of clinical psychology Robert F. Krueger and doctoral students Jaime Derringer and Abigail Powers:

PEOPLE OFTEN GO OUT OF THEIR WAY TO HELP perfect strangers for no apparent personal gain. Many of us assume that altruism is something that parents teach—be nice,
don’t talk with your mouth full, do unto others.... But science says that altruistic impulses are largely instinctive.

Compelling evidence that altruism is a genetic trait comes from studying our close relative, the chimpanzee. Chimps don’t teach their young to be nice the way humans do, but in 2007 scientists at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, found that chimps do behave selflessly, helping their human caretakers reach a stick or unfamiliar chimps open a cage full of food, without expecting a reward.

Soon after, another team from the same Max Planck Institute found evidence that altruistic behavior is innate in humans as well. In 2009 the researchers reported that infants younger than 18 months engaged in altruistic acts, such as helping adults reach objects or open cabinet doors. The infants’ attention to the needs of others most likely preceded their
full understanding of the social pressures associated with being selfless.

Genes, however, do not tell the full story of what prompts people to be generous. By examining altruism in identical twins, who share nearly 100 percent of their genes, and fraternal twins, who share 50 percent of their genes, researchers can estimate the extent to which genes and the environment contribute to selfless inclinations and behaviors. Overall, these twin studies suggest that genes explain between 30 and 60 percent of altruistic tendencies, with the remaining variation coming from cultural or social effects.

Interestingly, some studies indicate that the influence of genes may vary over time. For example, scientists in the U.K. showed that altruistic behaviors in younger children arose mostly from their environment, such as the family’s belief system. In the teenage years, however, when youths typically become more independent, genes have a much stronger influence on altruism.

What is going on in the brain when we experience déjà vu?
—Jennifer Cashen, Carrboro, N.C.

Paul Reber, a psychology professor at Northwestern University, answers:

ALTHOUGH SCIENTISTS HAVE not pinpointed exactly what goes on in the brain when a person experiences déjà vu, they can make good guesses based on models of memory. All theories of memory acknowledge that remembering requires two cooperating processes: familiarity and recollection. Familiarity occurs quickly, before the brain can recall the source of the feeling. Conscious recollection depends on the hippocampus and prefrontal cortex, whereas familiarity depends on regions of the medial temporal cortex.

When these cooperating processes get out of sync, we can experience déjà vu, the intense and often disconcerting feeling that a situation is familiar even though it has never happened before. This feeling can occur when a brand-new situation is very similar to other events stored in our memory. For example, a Texas airport may seem vaguely familiar to you even though you have never been to Texas. It is possible the airport is strikingly similar to a single event stored in memory—perhaps you recently saw the airport in a movie or magazine. It is also possible that many memories of visiting similar airports create the sensation that you have been to this one. Déjà vu is a stronger version of this kind of memory error.


The best evidence for a neural mechanism for déjà vu, which around 60 percent of people experience at least once, comes from studies of patients who experience it chronically. In 2005 cognitive neuropsychologists at the University of Leeds in England described two patients with recurring and persistent feelings of déjà vu. The patients refused to read a newspaper or watch television because they felt as if they had already seen it all before. They found it difficult to shop for groceries because they thought they had just purchased those items. The researchers discovered that these patients had damage to their frontal and temporal regions. Harm to these areas likely caused the patients’ familiarity circuitry to fire frequently, even when they were in a novel situation. In undamaged brains, déjà vu likely occurs because of processing errors in these same regions.